| 1. |
- Ackerley, Rochelle, 1980, et al.
(författare)
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Case Studies in Neuroscience: Sensations elicited and discrimination ability from nerve cuff stimulation in an amputee over time
- 2018
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 120:1, s. 291-295
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Tidskriftsartikel (refereegranskat)abstract
- The present case study details sensations elicited by electrical stimulation of peripheral nerve axons using an implanted nerve cuff electrode, in a participant with a transhumeral amputation. The participant uses an osseointegrated electromechanical interface, which enables skeletal attachment of the prosthesis and long-term, stable, bidirectional communication between the implanted electrodes and prosthetic arm. We focused on evoking somatosensory percepts, where we tracked and quantified the evolution of perceived sensations in the missing hand. which were evoked from electrical stimulation of the nerve, for over 2 yr. These sensations included small, pointlike areas of either vibration or pushing, to larger sensations over wider areas, indicating the recruitment of a few and many afferents, respectively. Furthermore, we used a two-alternative forced choice paradigm to measure the level of discrimination between trains of brief electrical stimuli, to gauge what the participant could reliably distinguish between. At best, the participant was able to distinguish a 05-Hz difference and on average acquired a 3.8-Hz just-noticeable difference at a more stringent psychophysical level. The current work shows the feasibility for long-term sensory feedback in prostheses, via electrical axonal stimulation, where small and relatively stable percepts were felt that may be used to deliver graded sensory feedback. This opens up opportunities for signaling feedback during movements (e.g., for precision grip), but also for conveying more complex cutaneous sensations. such as texture. NEW & NOTEWORTHY We demonstrate the long-term stability and generation of sensations from electrical peripheral nerve stimulation in an amputee. through an osseointegrated implant. We find that perceived tactilelike sensations could be generated for over 2 yr. in the missing hand. This is useful for prosthetic development and the implementation of feedback in artificial body parts.
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| 2. |
- Ackerley, Rochelle, 1980, et al.
(författare)
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Differential effects of radiant and mechanically applied thermal stimuli on human C-tactile afferent firing patterns.
- 2018
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 120:4, s. 1885-1892
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Tidskriftsartikel (refereegranskat)abstract
- C-tactile (CT) afferents respond to gentle tactile stimulation, but only a handful of studies in humans and animals have investigated whether their firing is modified by temperature. We describe the effects of radiant thermal stimuli, and of stationary and very slowly moving mechanothermal stimuli, on CT afferent responses. We find that CT afferents are primarily mechanoreceptors, as they fired little during radiant thermal stimuli, but they exhibited different patterns of firing during combined mechano-cool stimulation compared with warming. CTs fired optimally to gentle, very slowly moving, or stationary mechanothermal stimuli delivered at neutral temperature (~32°C, normal skin temperature), but they responded with fewer spikes (median 67% decrease) and at significantly lower rates (47% decrease) during warm (~42°C) tactile stimuli. During cool tactile stimuli (~18°C), their mean instantaneous firing frequency significantly decreased by 35%, but they often fired a barrage of afterdischarge spikes at a low frequency (~5 Hz) that outlasted the mechanical stimulus. These effects were observed under a variety of stimulus conditions, including during stationary and slowly moving touch (0.1 cm/s), and we complemented these tactile approaches using a combined electrical-thermal stimulation experiment where we found a suppression of spiking during warming. Overall, CT afferents are exquisitely sensitive to tactile events, and we show that their firing is modulated with touch temperatures above and below neutral skin temperature. Warm touch consistently decreased their propensity to fire, whereas cool touch produced lower firing rates but afterdischarge spiking. NEW & NOTEWORTHY C-tactile (CT) afferents are thought to underpin pleasant touch, and previous work has shown that they respond optimally to a slow caress delivered at typical (neutral) skin temperature. Here, we show that, although CTs are primarily mechanoreceptive afferents, they are modified by temperature: warm touch decreases their firing, whereas cool touch produces lower firing rates but long-lasting spiking, frequently seen as afterdischarges. This has implications for the encoding of affective sensory events in human skin.
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| 3. |
- Ackerley, Rochelle, 1980, et al.
(författare)
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Microneurography as a tool to study the function of individual C-fiber afferents in humans: responses from nociceptors, thermoreceptors, and mechanoreceptors
- 2018
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 120:6, s. 2834-2846
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Tidskriftsartikel (refereegranskat)abstract
- The technique of microneurography-recording neural traffic from nerves in awake humans-has provided us with unrivaled insights into afferent and efferent processes in the peripheral nervous system for over 50 years. We review the use of microneurography to study single C-fiber afferents and provide an overview of the knowledge gained, with views to future investigations. C-fibers have slowly conducting, thin-diameter, unmyelinated axons and make up the majority of the fibers in peripheral nerves (similar to 80%). With the use of microneurography in humans, C-fiber afferents have been differentiated into discrete subclasses that encode specific qualities of stimuli on the skin, and their functional roles have been investigated. Afferent somatosensory information provided by C-fibers underpins various positive and negative affective sensations from the periphery, including mechanical, thermal, and chemical pain (C-nociceptors), temperature (C-thermoreceptors), and positive affective aspects of touch (C-tactile afferents). Insights from microneurographic investigations have revealed the complexity of the C-fiber system, methods for delineating fundamental C-fiber populations in a translational manner, how C-fiber firing can be used to identify nerve deficits in pathological states, and how the responses from C-fibers may be modified to change sensory percepts, including decreasing pain. Understanding these processes may lead to future medical interventions to diagnose and treat C-fiber dysfunction. NEW & NOTEWORTHY The technique of microneurography allows us to directly investigate the functional roles of single C-fiber afferents in awake human beings. Here we outline and discuss the current field of C-fiber research on this heterogeneous population of afferents in healthy subjects, in pathological states, and from a translational perspective. We cover C-fibers encoding touch, temperature, and pain and provide perspectives on the future of C-fiber microneurography investigations in humans.
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| 4. |
- Agnati, LF, et al.
(författare)
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Functional roles of three cues that provide nonsynaptic modes of communication in the brain: electromagnetic field, oxygen, and carbon dioxide
- 2018
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 119:1, s. 356-368
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Tidskriftsartikel (refereegranskat)abstract
- The integrative actions of the brain depend on the exchange of information among its computational elements. Hence, this phenomenon plays the key role in driving the complex dynamics of the central nervous system, in which true computations interact with noncomputational dynamical processes to generate brain representations of the body and of the body in the external world, and hence the finalistic behavior of the organism. In this context, it should be pointed out that, besides the intercellular interactions mediated by classical electrochemical signals, other types of interactions, namely, “cues” and “coercions,” also appear to be exploited by the system to achieve its function. The present review focuses mainly on cues present in the environment and on those produced by cells of the body, which “pervade” the brain and contribute to its dynamics. These cues can also be metabolic substrates, and, in most cases, they are of fundamental importance to brain function and the survival of the entire organism. Three of these highly pervasive cues will be analyzed in greater detail, namely, oxygen, carbon dioxide, and electromagnetic fields (EMF). Special emphasis will be placed on EMF, since several authors have suggested that these highly pervasive energy fluctuations may play an important role in the global integrative actions of the brain; hence, EMF signaling may transcend classical connectionist models of brain function. Thus the new concept of “broadcasted neuroconnectomics” has been introduced, which transcends the current connectomics view of the brain.
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| 5. |
- Almeida, R, et al.
(författare)
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Neural circuit basis of visuo-spatial working memory precision: a computational and behavioral study
- 2015
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 114:3, s. 1806-1818
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Tidskriftsartikel (refereegranskat)abstract
- The amount of information that can be retained in working memory (WM) is limited. Limitations of WM capacity have been the subject of intense research, especially in trying to specify algorithmic models for WM. Comparatively, neural circuit perspectives have barely been used to test WM limitations in behavioral experiments. Here we used a neuronal microcircuit model for visuo-spatial WM (vsWM) to investigate memory of several items. The model assumes that there is a topographic organization of the circuit responsible for spatial memory retention. This assumption leads to specific predictions, which we tested in behavioral experiments. According to the model, nearby locations should be recalled with a bias, as if the two memory traces showed attraction or repulsion during the delay period depending on distance. Another prediction is that the previously reported loss of memory precision for an increasing number of memory items (memory load) should vanish when the distances between items are controlled for. Both predictions were confirmed experimentally. Taken together, our findings provide support for a topographic neural circuit organization of vsWM, they suggest that interference between similar memories underlies some WM limitations, and they put forward a circuit-based explanation that reconciles previous conflicting results on the dependence of WM precision with load.
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| 6. |
- Baczyk, Marcin, et al.
(författare)
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Long-term effects of direct current are reproduced by intermittent depolarization of myelinated nerve fibers
- 2018
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 120:3, s. 1173-1185
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Tidskriftsartikel (refereegranskat)abstract
- Direct current (DC) potently increases the excitability of myelinated afferent fibers in the dorsal columns, both during DC polarization of these fibers and during a considerable (>1 h) postpolarization period. The aim of the present study was to investigate whether similarly long-lasting changes in the excitability of myelinated nerve fibers in the dorsal columns may be evoked by field potentials following stimulation of peripheral afferents and by subthreshold epidurally applied current pulses. The experiments were performed in deeply anesthetized rats. The effects were monitored by changes in nerve volleys evoked in epidurally stimulated hindlimb afferents and in the synaptic actions of these afferents. Both were found to be facilitated during as well as following stimulation of a skin nerve and during as well as following epidurally applied current pulses of 5- to 10-ms duration. The facilitation occurring <= 2 min after skin nerve stimulation could be linked to both primary afferent depolarization and large dorsal horn field potentials, whereas the subsequent changes (up to 1 h) were attributable to effects of the field potentials. The findings lead to the conclusion that the modulation of spinal activity evoked by DC does not require long-lasting polarization and that relatively short current pulses and intrinsic field potentials may contribute to plasticity in spinal activity. These results suggest the possibility of enhancing the effects of epidural stimulation in human subjects by combining it with polarizing current pulses and peripheral afferent stimulation and not only with continuous DC. NEW & NOTEWORTHY The aim of this study was to define conditions under which a long-term. increase is evoked in the excitability of myelinated nerve fibers. The results demonstrate that a potent and long-lasting increase in the excitability of afferent fibers traversing the dorsal columns may be induced by synaptically evoked intrinsic field as well as by epidurally applied intermittent current pulses. They thus provide a new means for the facilitation of the effects of epidural stimulation.
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| 7. |
- Baugh, Lee A., et al.
(författare)
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Representing multiple object weights : competing priors and sensorimotor memories
- 2016
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 116:4, s. 1615-1625
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Tidskriftsartikel (refereegranskat)abstract
- When lifting an object, individuals scale lifting forces based on long-term priors relating external object properties (such as material and size) to object weight. When experiencing objects that are poorly predicted by priors, people rapidly form and update sensorimotor memories that can be used to predict an object's atypical size-weight relation in support of predictively scaling lift forces. With extensive experience in lifting such objects, long-term priors, assessed with weight judgments, are gradually updated. The aim of the present study was to understand the formation and updating of these memory processes. Participants lifted, over multiple days, a set of black cubes with a normal size-weight mapping and green cubes with an inverse size-weight mapping. Sensorimotor memory was assessed with lifting forces, and priors associated with the black and green cubes were assessed with the size-weight illusion (SWI). Interference was observed in terms of adaptation of the SWI, indicating that priors were not independently adjusted. Half of the participants rapidly learned to scale lift forces appropriately, whereas reduced learning was observed in the others, suggesting that individual differences may be affecting sensorimotor memory abilities. A follow-up experiment showed that lifting forces are not accurately scaled to objects when concurrently performing a visuomotor association task, suggesting that sensorimotor memory formation involves cognitive resources to instantiate the mapping between object identity and weight, potentially explaining the results of experiment 1. These results provide novel insight into the formation and updating of sensorimotor memories and provide support for the independent adjustment of sensorimotor memory and priors.
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| 8. |
- Borch Petersen, Eline, et al.
(författare)
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Neural tracking of attended versus ignored speech is differentially affected by hearing loss
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 117:1, s. 18-27
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Tidskriftsartikel (refereegranskat)abstract
- Hearing loss manifests as a reduced ability to understand speech, particularly in multitalker situations. In these situations, younger normal-hearing listeners' brains are known to track attended speech through phase-locking of neural activity to the slow-varying envelope of the speech. This study investigates how hearing loss, compensated by hearing aids, affects the neural tracking of the speech-onset envelope in elderly participants with varying degree of hearing loss (n = 27, 62–86 yr; hearing thresholds 11–73 dB hearing level). In an active listening task, a to-be-attended audiobook (signal) was presented either in quiet or against a competing to-be-ignored audiobook (noise) presented at three individualized signal-to-noise ratios (SNRs). The neural tracking of the to-be-attended and to-be-ignored speech was quantified through the cross-correlation of the electroencephalogram (EEG) and the temporal envelope of speech. We primarily investigated the effects of hearing loss and SNR on the neural envelope tracking. First, we found that elderly hearing-impaired listeners' neural responses reliably track the envelope of to-be-attended speech more than to-be-ignored speech. Second, hearing loss relates to the neural tracking of to-be-ignored speech, resulting in a weaker differential neural tracking of to-be-attended vs. to-be-ignored speech in listeners with worse hearing. Third, neural tracking of to-be-attended speech increased with decreasing background noise. Critically, the beneficial effect of reduced noise on neural speech tracking decreased with stronger hearing loss. In sum, our results show that a common sensorineural processing deficit, i.e., hearing loss, interacts with central attention mechanisms and reduces the differential tracking of attended and ignored speech.
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| 9. |
- Dione, Mariama, 1987, et al.
(författare)
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Human 8-to 10-Hz pulsatile motor output during active exploration of textured surfaces reflects the textures' frictional properties
- 2019
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 122:3, s. 922-932
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Tidskriftsartikel (refereegranskat)abstract
- Active sensing in biological system consists of emitting/receiving a periodic signal to explore the environment. The signal can be emitted toward distant objects. as in echolocation, or in direct contact with the object. for example, whisking in rodents. We explored the hypothesis that a similar mechanism exists in humans. Humans generate periodic signals at similar to 10 Hz during voluntary finger movements, which reflects a pulsatile motor command in the central nervous system. In the present study, we tested whether the similar to 10-Hz signal persists during the active exploration of textures and whether the textures' features can modulate the signal. Our results confirm our assumptions. The similar to 10-Ilz signal persisted during active touch, and its amplitude increased with textures of higher friction. These findings support the idea that the similar to 10-Hz periodic signal generated during voluntary finger movements is part of an active sensing mechanism acting in a pulse-amplitude modulation fashion to convey relevant tactile information to the brain. NEW & NOTEWORTHY For the first time, we show that pulsatile motor output during voluntary movement of a finger persists during active exploration of a surface. We propose that this is part of an active sensing system in humans, with generation of an similar to 10-Hz signal during active touch that reinforces extraction of information about features of the touched surface.
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| 10. |
- Fardo, F, et al.
(författare)
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Delta and gamma oscillations in operculo-insular cortex underlie innocuous cold thermosensation
- 2017
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 117:5, s. 1959-1968
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Tidskriftsartikel (refereegranskat)abstract
- Cold-sensitive and nociceptive neural pathways interact to shape the quality and intensity of thermal and pain perception. Yet the central processing of cold thermosensation in the human brain has not been extensively studied. Here, we used magnetoencephalography and EEG in healthy volunteers to investigate the time course (evoked fields and potentials) and oscillatory activity associated with the perception of cold temperature changes. Nonnoxious cold stimuli consisting of Δ3°C and Δ5°C decrements from an adapting temperature of 35°C were delivered on the dorsum of the left hand via a contact thermode. Cold-evoked fields peaked at around 240 and 500 ms, at peak latencies similar to the N1 and P2 cold-evoked potentials. Importantly, cold-related changes in oscillatory power indicated that innocuous thermosensation is mediated by oscillatory activity in the range of delta (1–4 Hz) and gamma (55–90 Hz) rhythms, originating in operculo-insular cortical regions. We suggest that delta rhythms coordinate functional integration between operculo-insular and frontoparietal regions, while gamma rhythms reflect local sensory processing in operculo-insular areas. NEW & NOTEWORTHY Using magnetoencephalography, we identified spatiotemporal features of central cold processing, with respect to the time course, oscillatory profile, and neural generators of cold-evoked responses in healthy human volunteers. Cold thermosensation was associated with low- and high-frequency oscillatory rhythms, both originating in operculo-insular regions. These results support further investigations of central cold processing using magnetoencephalography or EEG and the clinical utility of cold-evoked potentials for neurophysiological assessment of cold-related small-fiber function and damage.
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| 11. |
- Fiath, Richard, et al.
(författare)
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Large-scale recording of thalamocortical circuits : in vivo electrophysiology with the two-dimensional electronic depth control silicon probe
- 2016
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 116:5, s. 2312-2330
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Tidskriftsartikel (refereegranskat)abstract
- Recording simultaneous activity of a large number of neurons in distributed neuronal networks is crucial to understand higher order brain functions. We demonstrate the in vivo performance of a recently developed electrophysiological recording system comprising a two-dimensional, multi-shank, high-density silicon probe with integrated complementary metal-oxide semiconductor electronics. The system implements the concept of electronic depth control (EDC), which enables the electronic selection of a limited number of recording sites on each of the probe shafts. This innovative feature of the system permits simultaneous recording of local field potentials (LFP) and single-and multiple-unit activity (SUA and MUA, respectively) from multiple brain sites with high quality and without the actual physical movement of the probe. To evaluate the in vivo recording capabilities of the EDC probe, we recorded LFP, MUA, and SUA in acute experiments from cortical and thalamic brain areas of anesthetized rats and mice. The advantages of large-scale recording with the EDC probe are illustrated by investigating the spatiotemporal dynamics of pharmacologically induced thalamocortical slow-wave activity in rats and by the two-dimensional tonotopic mapping of the auditory thalamus. In mice, spatial distribution of thalamic responses to optogenetic stimulation of the neocortex was examined. Utilizing the benefits of the EDC system may result in a higher yield of useful data from a single experiment compared with traditional passive multielectrode arrays, and thus in the reduction of animals needed for a research study.
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| 12. |
- Filingeri, D., et al.
(författare)
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The biology of skin wetness perception and its implications in manual function and for reproducing complex somatosensory signals in neuroprosthetics
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 117:4, s. 1761-1775
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Tidskriftsartikel (refereegranskat)abstract
- Our perception of skin wetness is generated readily, yet humans have no known receptor (hygroreceptor) to signal this directly. It is easy to imagine the sensation of water running over our hands or the feel of rain on our skin. The synthetic sensation of wetness is thought to be produced from a combination of specific skin thermal and tactile inputs, registered through thermoreceptors and mechanoreceptors, respectively. The present review explores how thermal and tactile afference from the periphery can generate the percept of wetness centrally. We propose that the main signals include information about skin cooling, signaled primarily by thinly myelinated thermoreceptors, and rapid changes in touch, through fast-conducting, myelinated mechanoreceptors. Potential central sites for integration of these signals, and thus the perception of skin wetness, include the primary and secondary somatosensory cortices and the insula cortex. The interactions underlying these processes can also be modeled to aid in understanding and engineering the mechanisms. Furthermore, we discuss the role that sensing wetness could play in precision grip and the dexterous manipulation of objects. We expand on these lines of inquiry to the application of the knowledge in designing and creating skin sensory feedback in prosthetics. The addition of real-time, complex sensory signals would mark a significant advance in the use and incorporation of prosthetic body parts for amputees in everyday life. NEW & NOTEWORTHY Little is known about the underlying mechanisms that generate the perception of skin wetness. Humans have no specific hygroreceptor, and thus temperature and touch information combine to produce wetness sensations. The present review covers the potential mechanisms leading to the perception of wetness, both peripherally and centrally, along with their implications for manual function. These insights are relevant to inform the design of neuroengineering interfaces, such as sensory prostheses for amputees.
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| 13. |
- Filipovic, Marko, et al.
(författare)
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Direct pathway neurons in mouse dorsolateral striatum in vivo receive stronger synaptic input than indirect pathway neurons
- 2019
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Ingår i: Journal of Neurophysiology. - : AMER PHYSIOLOGICAL SOC. - 0022-3077 .- 1522-1598. ; 122:6, s. 2294-2303
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Tidskriftsartikel (refereegranskat)abstract
- Striatal projection neurons, the medium spiny neurons (MSNs), play a crucial role in various motor and cognitive functions. MSNs express either D1- or D2-type dopamine receptors and initiate the direct-pathway (dMSNs) or indirect pathways (iMSNs) of the basal ganglia, respectively. dMSNs have been shown to receive more inhibition than iMSNs from intrastriatal sources. Based on these findings, computational modeling of the suiatal network has predicted that under healthy conditions dMSNs should receive more total input than iMSNs. To test this prediction, we analyzed in vivo whole cell recordings from dMSNs and iMSNs in healthy and dopamine-depleted (60HDA) anaesthetized mice. By comparing their membrane potential fluctuations, we found that dMSNs exhibited considerably larger membrane potential fluctuations over a wide frequency range. Furthermore, by comparing the spike-triggered average membrane potentials. we found that dMSNs depolarized toward the spike threshold significantly faster than iMSNs did. Together, these findings (in particular the STA analysis) corroborate the theoretical prediction that direct-pathway MSNs receive stronger total input than indirect-pathway neurons. Finally, we found that dopamine-depleted mice exhibited no difference between the membrane potential fluctuations of dMSNs and iMSNs. These data provide new insights into the question of how the lack of dopamine may lead to behavioral deficits associated with Parkinson's disease. NEW & NOTEWORTHY The direct and indirect pathways of the basal ganglia originate from the D1- and D2-type dopamine receptor expressing medium spiny neurons (dMSNs and iMSNs). Theoretical results have predicted that dMSNs should receive stronger synaptic input than iMSNs. Using in vivo intracellular membrane potential data, we provide evidence that dMSNs indeed receive stronger input than iMSNs, as has been predicted by the computational model.
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| 14. |
- Folmli, Brookes, et al.
(författare)
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Dose-response of somatosensory cortex repeated anodal transcranial direct current stimulation on vibrotactile detection : A randomized sham controlled trial
- 2018
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Ingår i: Journal of Neurophysiology. - Bethesda, United States : American Physiological Society. - 0022-3077 .- 1522-1598.
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Tidskriftsartikel (refereegranskat)abstract
- This randomized sham-controlled trial investigated anodal transcranial direct current stimulation (tDCS) over the somatosensory cortex contralateral to hand dominance for dose-response (1mA-20 minutes x 5 days) effects on vibrotactile detection thresholds (VDT). VDT was measured before and after tDCS on days 1,3&5 for low (30hz) and high (200hz) frequency vibrations on the dominant and non-dominant hands in 29 healthy adults (mean age = 22.86; 15 males, 14 females). Only the dominant hand 200Hz VDT displayed statistically significant medium effect size improvement for mixed model analysis of variance time x group interaction for active tDCS compared to sham. Post Hoc contrasts were statistically significant for dominant hand 200Hz VDT on day 5 after tDCS compared to day 1 before tDCS , day 1 after tDCS and day 3 before tDCS. There was a linear dose-response improvement with dominant hand 200Hz VDT mean difference decreasing from day 1 before tDCS peaking at -15.5% (SD=34.9%) on day 5 after tDCS. Both groups showed learning effect trends over time for all VDT test conditions but only the non-dominant hand 30Hz VDT was statistically significant (p=0.03) though Post Hoc contrasts were non-significant after Sidak adjustment. No adverse effects for tDCS were reported. In conclusion, anodal tDCS 1mA-20 minutes x 5 days on the dominant sensory cortex can modulate a linear improvement of dominant hand high frequency VDT but not for low frequency or non-dominant hand VDT.
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| 15. |
- Halje, Pär, et al.
(författare)
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Oscillations in cortico-basal ganglia circuits : implications for Parkinson's disease and other neurologic and psychiatric conditions
- 2019
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Ingår i: Journal of Neurophysiology. - : AMER PHYSIOLOGICAL SOC. - 0022-3077 .- 1522-1598. ; 122:1, s. 203-231
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Forskningsöversikt (refereegranskat)abstract
- Cortico-basal ganglia circuits are thought to play a crucial role in the selection and control of motor behaviors and have also been implicated in the processing of motivational content and in higher cognitive functions. During the last two decades, electro-physiological recordings in basal ganglia circuits have shown that several disease conditions are associated with specific changes in the temporal patterns of neuronal activity. In particular, synchronized oscillations have been a frequent finding suggesting that excessive synchronization of neuronal activity may be a pathophysiological mechanism involved in a wide range of neurologic and psychiatric conditions. We here review the experimental support for this hypothesis primarily in relation to Parkinson's disease but also in relation to dystonia, essential tremor, epilepsy, and psychosis/schizophrenia.
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| 16. |
- Hudson, K. M., et al.
(författare)
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Effects of changing skin mechanics on the differential sensitivity to surface compliance by tactile afferents in the human finger pad
- 2015
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 114:4, s. 2249-2257
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Tidskriftsartikel (refereegranskat)abstract
- It is not known how changes in skin mechanics affect the responses of cutaneous mechanoreceptors in the finger pads to compression forces. We used venous occlusion to change the stiffness of the fingers and investigated whether this influenced the firing of low-threshold mechanoreceptors to surfaces of differing stiffness. Unitary recordings were made from 10 slowly adapting type I (SAI), 10 fast adapting type I (FAI) and 9 slowly adapting type II (SAII) units via tungsten microelectrodes inserted into the median nerve at the wrist. A servocontrolled stimulator applied ramp-and-hold forces (1, 2, and 4 N) at a constant loading and unloading rate (2 N/s) via a flat 2.5-cmdiameter silicone disk over the center of the finger pad. Nine silicone disks (objects), varying in compliance, were used. Venous occlusion, produced by inflating a sphygmomanometer cuff around the upper arm to 40±5 mmHg, was used to induce swelling of the fingers and increase the compliance of the finger pulp. Venous occlusion had no effect on the firing rates of the SAI afferents, nor on the slopes of the relationship between mean firing rate and object compliance at each amplitude, but did significantly reduce the slopes for the FAI afferents. Although the SAII afferents possess a poor capacity to encode changes in object compliance, mean firing rates were significantly lower during venous occlusion. The finding that venous occlusion had no effect on the firing properties of SAI afferents indicates that these afferents preserve their capacity to encode changes in object compliance, despite changes in skin mechanics. © 2015 the American Physiological Society.
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| 17. |
- Israeli-Korn, SD, et al.
(författare)
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Intersegmental coordination patterns are differently affected in Parkinson's disease and cerebellar ataxia
- 2019
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 121:2, s. 672-689
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Tidskriftsartikel (refereegranskat)abstract
- The law of intersegmental coordination (Borghese et al. 1996) may be altered in pathological conditions. Here we investigated the contribution of the basal ganglia (BG) and the cerebellum to lower limb intersegmental coordination by inspecting the plane’s orientation and other parameters pertinent to this law in patients with idiopathic Parkinson’s disease (PD) or cerebellar ataxia (CA). We also applied a mathematical model that successfully accounts for the intersegmental law of coordination observed in control subjects (Barliya et al. 2009). In the present study, we compared the planarity index (PI), covariation plane (CVP) orientation, and CVP orientation predicted by the model in 11 PD patients, 8 CA patients, and two groups of healthy subjects matched for age, height, weight, and gender to each patient group (Ctrl_PD and Ctrl_CA). Controls were instructed to alter their gait speed to match those of their respective patient group. PD patients were examined after overnight withdrawal of anti-parkinsonian medications (PD-off-med) and then on medication (PD-on-med). PI was above 96% in all gait conditions in all groups suggesting that the law of intersegmental coordination is preserved in both BG and cerebellar pathology. However, the measured and predicted CVP orientations rotated in PD-on-med and PD-off-med compared with Ctrl_PD and in CA vs. Ctrl_CA. These rotations caused by PD and CA were in opposite directions suggesting differences in the roles of the BG and cerebellum in intersegmental coordination during human locomotion. NEW & NOTEWORTHY Kinematic and muscular synergies may have a role in overcoming motor redundancies, which may be reflected in intersegmental covariation. Basal ganglia and cerebellar networks were suggested to be involved in crafting and modulating synergies. We thus compared intersegmental coordination in Parkinson’s disease and cerebellar disease patients and found opposite effects in some aspects. Further research integrating muscle activities as well as biomechanical and neural control modeling are needed to account for these findings.
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| 18. |
- Jankowska, Elzbieta, et al.
(författare)
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Long-lasting increase in axonal excitability after epidurally applied DC
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 118:2, s. 1210-1220
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Tidskriftsartikel (refereegranskat)abstract
- Effects of direct current (DC) on nerve fibers have primarily been investigated during or just after DC application. However, locally applied cathodal DC was recently demonstrated to increase the excitability of intraspinal preterminal axonal branches for >1 h. The aim of this study was therefore to investigate whether DC evokes a similarly long-lasting increase in the excitability of myelinated axons within the dorsal columns. The excitability of dorsal column fibers stimulated epidurally was monitored by recording compound action potentials in peripheral nerves in acute experiments in deeply anesthetized rats. The results show that 1) cathodal polarization (0.8–1.0 μA) results in a severalfold increase in the number of epidurally activated fibers and 2) the increase in the excitability appears within seconds, 3) lasts for >1 h, and 4) is activity independent, as it does not require fiber stimulation during the polarization. These features demonstrate an unexplored form of plasticity of myelinated fibers and indicate the conditions under which it develops. They also suggest that therapeutic effects of epidural stimulation may be significantly enhanced if it is combined with DC polarization. In particular, by using DC to increase the number of fibers activated by low-intensity epidural stimuli, the low clinical tolerance to higher stimulus intensities might be overcome. The activity independence of long-lasting DC effects would also allow the use of only brief periods of DC polarization preceding epidural stimulation to increase the effect. NEW & NOTEWORTHY The study indicates a new form of plasticity of myelinated fibers. The differences in time course of DC-evoked increases in the excitability of myelinated nerve fibers in the dorsal columns and in preterminal axonal branches suggest that distinct mechanisms are involved in them. The results show that combining epidural stimulation and transspinal DC polarization may dramatically improve their outcome and result in more effective pain control and the return of impaired motor functions. © 2017 the American Physiological Society.
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| 19. |
- Jankowska, Elzbieta
(författare)
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Spinal control of motor outputs by intrinsic and externally induced electric field potentials
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 118:2, s. 1221-1234
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Tidskriftsartikel (refereegranskat)abstract
- Despite numerous studies on spinal neuronal systems, several issues regarding their role in motor behavior remain unresolved. One of these issues is how electric fields associated with the activity of spinal neurons influence the operation of spinal neuronal networks and how effects of these field potentials are combined with other means of modulating neuronal activity. Another closely related issue is how external electric field potentials affect spinal neurons and how they can be used for therapeutic purposes such as pain relief or recovery of motor functions by transspinal direct current stimulation. Nevertheless, progress in our understanding of the spinal effects of electric fields and their mechanisms has been made over the last years, and the aim of the present review is to summarize the recent findings in this field.
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| 20. |
- Kleberg, Johan Lundin
(författare)
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Resting state arousal and functional connectivity in autism spectrum disorder
- 2015
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 113:9, s. 3035-3037
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Tidskriftsartikel (refereegranskat)abstract
- A recent study (Eilam-Stock T, Xu P, Cao M, Gu X, Van Dam NT, Anagnostou E, Kolevzon A, Soorya L, Park Y, Siller M, He Y, Hof PR, Fan J. Brain 137: 153-171, 2014) demonstrated that resting state electrodermal activity is correlated with different patterns of brain activity in subjects with autism spectrum disorder (ASD) than in typical controls. These results are considered in light of theories of atypical arousal in ASD.
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| 21. |
- Leao, Richardson N, et al.
(författare)
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Interconnection and Synchronization of Neuronal Populations in the Mouse Medial Septum/Diagonal Band of Brocca
- 2015
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 113:3, s. 971-980
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Tidskriftsartikel (refereegranskat)abstract
- The medial septum/diagonal band of Broca (MS/DBB) is crucial for hippocampal theta rhythm generation (4-12Hz). However, the mechanisms behind theta rhythmogenesis are still under debate. The MS/DBB consists, in its majority, of three neuronal populations that use either acetylcholine, GABA or glutamate as neurotransmitters. While the firing patterns of septal neurons enable the MS/DBB to generate rhythmic output critical for the generation of the hippocampal theta rhythm, the ability to synchronize these action potentials is dependent on the interconnectivity between the three major MS/DBB neuronal populations. Yet little is known about intraseptal connections. Here we assess the connectivity between pairs of MS/DBB neurons using paired patch-clamp recordings. We found that glutamatergic and GABAergic neurons provide intraseptal connections and produce sizable currents in MS/DBB postsynaptic cells. We also analyzed linear and non-linear relationships between the action potentials fired by pairs of neurons belonging to various MS/DBB neuronal populations. Our results show that while the synchrony index for action potential firing was significantly higher in pairs of GABAergic neurons coherence of action potential firing in the theta range was similarly low in all pairs analyzed. Recurrence analysis demonstrated that individual action potentials were more recurrent in cholinergic neurons than other cell types. Implementing sparse connectivity in a computer model of the MS/DBB network reproduced our experimental data. We conclude that the interplay between the intrinsic membrane properties of different MS/DBB neuronal populations and the connectivity amongst these populations underlies the ability of the MS/DBB network to critically contribute to hippocampal theta rhythmogenesis.
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| 22. |
- Macefield, V. G., et al.
(författare)
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Physiological and pathophysiological firing properties of single postganglionic sympathetic neurons in humans
- 2018
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 119:3, s. 944-956
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Tidskriftsartikel (refereegranskat)abstract
- It has long been known from microneurographic recordings in human subjects that the activity of postganglionic sympathetic axons occurs as spontaneous bursts, with muscle sympathetic nerve activity (MSNA) exhibiting strong cardiac rhythmicity via the baroreflex and skin sympathetic nerve activity showing much weaker cardiac modulation. Here we review the firing properties of single sympathetic neurons, obtained using highly selective microelectrodes. Individual vasoconstrictor neurons supplying muscle or skin, or sudomotor neurons supplying sweat glands, always discharge with a low firing probability (similar to 30%) and at very low frequencies (similar to 0.5 Hz). Moreover, they usually fire only once per cardiac interval but can fire greater than four times within a burst. Modeling has shown that this pattern can best be explained by individual neurons being driven by, on average, two preganglionic inputs. Unitary recordings of muscle vasoconstrictor neurons have been made in several pathophysiological states, including heart failure, hypertension, obstructive sleep apnea, bronchiectasis, chronic obstructive pulmonary disease, depression, and panic disorder. The augmented MSNA in each of these diseases features an increase in firing probability and discharge frequency of individual muscle vasoconstrictor neurons above that seen in healthy subjects, yet firing rates rarely exceed 1 Hz. However, unlike patients with heart failure, all patients with respiratory disease or panic disorder, and patients with hyperhidrosis, exhibited an increase in multiple within-burst firing, which emphasizes the different modes by which the sympathetic nervous system grades its output in pathophysiological states of high sympathetic nerve activity.
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| 23. |
- Maeda, Rodrigo S., et al.
(författare)
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Compensating for intersegmental dynamics across the shoulder, elbow, and wrist joints during feedforward and feedback control
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 118:4, s. 1984-1997
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Tidskriftsartikel (refereegranskat)abstract
- Moving the arm is complicated by mechanical interactions that arise between limb segments. Such intersegmental dynamics cause torques applied at one joint to produce movement at multiple joints, and in turn, the only way to create single joint movement is by applying torques at multiple joints. We investigated whether the nervous system accounts for intersegmental limb dynamics across the shoulder, elbow, and wrist joints during self-initiated planar reaching and when countering external mechanical perturbations. Our first experiment tested whether the timing and amplitude of shoulder muscle activity account for interaction torques produced during single-joint elbow movements from different elbow initial orientations and over a range of movement speeds. We found that shoulder muscle activity reliably preceded movement onset and elbow agonist activity, and was scaled to compensate for the magnitude of interaction torques arising because of forearm rotation. Our second experiment tested whether elbow muscles compensate for interaction torques introduced by single-joint wrist movements. We found that elbow muscle activity preceded movement onset and wrist agonist muscle activity, and thus the nervous system predicted interaction torques arising because of hand rotation. Our third and fourth experiments tested whether shoulder muscles compensate for interaction torques introduced by different hand orientations during self-initiated elbow movements and to counter mechanical perturbations that caused pure elbow motion. We found that the nervous system predicted the amplitude and direction of interaction torques, appropriately scaling the amplitude of shoulder muscle activity during self-initiated elbow movements and rapid feedback control. Taken together, our results demonstrate that the nervous system robustly accounts for intersegmental dynamics and that the process is similar across the proximal to distal musculature of the arm as well as between feedforward (i.e., self- initiated) and feedback (i.e., reflexive) control. NEW & NOTEWORTHY Intersegmental dynamics complicate the mapping between applied joint torques and the resulting joint motions. We provide evidence that the nervous system robustly predicts these intersegmental limb dynamics across the shoulder, elbow, and wrist joints during reaching and when countering external perturbations.
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| 24. |
- Parma, V, et al.
(författare)
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Motor signatures in autism spectrum disorder: the importance of variability
- 2016
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 115:3, s. 1081-1084
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Tidskriftsartikel (refereegranskat)abstract
- In a recent study, Wang et al. ( J Neurophysiol 113: 1989–2001, 2015) used a precision grip force control task to unveil the contribution of feedforward and feedback mechanisms to sensorimotor dysfunction in autism spectrum disorder (ASD). Impairment of both motor control mechanisms was observed, along with significant variability in the motor response. In this Neuro Forum article we discuss these findings within the conceptual framework of the grasping circuit and within the broader context of clinical and research applications based on motor behavior.
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| 25. |
- Perini, Irene, et al.
(författare)
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Rare human nerve growth factor-beta mutation reveals relationship between C-afferent density and acute pain evaluation
- 2016
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Ingår i: Journal of Neurophysiology. - : AMER PHYSIOLOGICAL SOC. - 0022-3077 .- 1522-1598. ; 116:2, s. 425-430
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Tidskriftsartikel (refereegranskat)abstract
- The rare nerve growth factor-beta (NGFB) mutation R221W causes a selective loss of thinly myelinated fibers and especially unmyelinated C-fibers. Carriers of this mutation show altered pain sensation. A subset presents with arthropathic symptoms, with the homozygous most severely affected. The aim of the present study was to investigate the relationship between peripheral afferent loss and pain evaluation by performing a quantification of small-fiber density in the cornea of the carriers, relating density to pain evaluation measures. In vivo corneal confocal microscopy (CCM) was used to quantify C-fiber loss in the cornea of 19 R221W mutation carriers (3 homozygous) and 19 age-matched healthy control subjects. Pain evaluation data via the Situational Pain Questionnaire (SPQ) and the severity of neuropathy based on the Neuropathy Disability Score (NDS) were assessed. Homozygotes, heterozygotes, and control groups differed significantly in corneal C-nerve fiber density, with the homozygotes showing a significant afferent reduction. Importantly, peripheral C-fiber loss correlated negatively with pain evaluation, as revealed by SPQ scores. This study is the first to investigate the contribution of small-fiber density to the perceptual evaluation of pain. It demonstrates that the lower the peripheral small-fiber density, the lower the degree of reported pain intensity, indicating a functional relationship between small-fiber density and higher level pain experience.
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| 26. |
- Puttaraksa, Gonthicha, et al.
(författare)
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Voluntary and tremorogenic inputs to motor neuron pools of agonist/antagonist muscles in essential tremor patients
- 2019
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 122:5, s. 2043-2053
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Tidskriftsartikel (refereegranskat)abstract
- Pathological tremor is an oscillation of body parts at 3-10 Hz, determined by the output of spinal motor neurons (MNs), which receive synaptic inputs from supraspinal centers and muscle afferents. The behavior of spinal MNs during tremor is not well understood, especially in relation to the activation of the multiple muscles involved. Recent studies on patients with essential tremor have shown that antagonist MN pools receive shared input at the tremor frequency. In this study, we investigated the synaptic inputs related to tremor and voluntary movement, and their coordination across antagonist muscles. We analyzed the spike trains of motor units (MUs) identified from high-density surface electromyography from the forearm extensor and flexor muscles in 15 patients with essential tremor during postural tremor. The shared synaptic input was quantified by coherence and phase difference analysis of the spike trains. All pairs of spike trains in each muscle showed coherence peaks at the voluntary drive frequency (1-3 Hz. 0.2 +/- 0.2, mean +/- SI)) and tremor frequency (3-10 Hz, 0.6 +/- 0.3) and were synchronized with small phase differences (3.3 +/- 25.2 degrees and 3.9 +/- 22.0 degrees for the voluntary drive and tremor frequencies. respectively). The coherence between MN spike trains of antagonist muscle groups at the tremor frequency was significantly smaller than intramuscular coherence. We predominantly observed in-phase activation of MUs between agonist/antagonist muscles at the voluntary frequency band (0.6 +/- 48.8 degrees) and out-of-phase activation at the tremor frequency band (126.9 +/- 75.6 degrees). Thus MNs innervating agonist/antagonist muscles concurrently receive synaptic inputs with different phase shifts in the voluntary and tremor frequency bands. NEW & NOTEWORTHY Although the mechanical characteristics of tremor have been widely studied, the activation of the affected muscles is still poorly understood. We analyzed the behavior of motor units of pairs of antagonistic wrist muscle groups in patients with essential tremor and studied their activity at voluntary movement- and tremor-related frequencies. We found that the phase relation between inputs to antagonistic muscles is different at the voluntary and tremor frequency bands.
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| 27. |
- Stienen, PJ, et al.
(författare)
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Precaution for volume conduction in rodent cortical electroencephalography using high-density polyimide-based microelectrode arrays on the skull
- 2016
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 115:4, s. 1970-1977
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Tidskriftsartikel (refereegranskat)abstract
- In humans, significant progress has been made to link spatial changes in electroencephalographic (EEG) spectral density, connectivity strength, and phase-amplitude modulation to neurological, physiological, and psychological correlates. In contrast, standard rodent EEG techniques employ only few electrodes, which results in poor spatial resolution. Recently, a technique was developed to overcome this limitation in mice. This technique was based on a polyimide-based microelectrode (PBM) array applied on the mouse skull, maintaining a significant number of electrodes with consistent contact, electrode impedance, and mechanical stability. The present study built on this technique by extending it to rats. Therefore, a similar PBM array, but adapted to rats, was designed and fabricated. In addition, this array was connected to a wireless EEG headstage, allowing recording in untethered, freely moving rats. The advantage of a high-density array relies on the assumption that the signal recorded from the different electrodes is generated from distinct sources, i.e., not volume-conducted. Therefore, the utility and validity of the array were evaluated by determining the level of synchrony between channels due to true synchrony or volume conduction during basal vigilance states and following a subanesthetic dose of ketamine. Although the PBM array allowed recording with high signal quality, under both drug and drug-free conditions, high synchronization existed due to volume conduction between the electrodes even in the higher spectral frequency range. Discrimination existed only between frontally and centrally/distally grouped electrode pairs. Therefore, caution should be used in interpreting spatial data obtained from high-density PBM arrays in rodents.
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| 28. |
- Svensson, Erik, et al.
(författare)
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The modulation of two motor behaviors by persistent sodium currents in Xenopus laevis tadpoles
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 118:1, s. 121-130
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Tidskriftsartikel (refereegranskat)abstract
- Persistent sodium currents (I-NaP) are common in neuronal circuitries and have been implicated in several diseases, such as amyotrophic lateral sclerosis (ALS) and epilepsy. However, the role of I-NaP in the regulation of specific behaviors is still poorly understood. In this study we have characterized I-NaP and investigated its role in the swimming and struggling behavior of Xenopus tadpoles. I-NaP was identified in three groups of neurons, namely, sensory Rohon-Beard neurons (RB neurons), descending interneurons (dINs), and non-dINs (neurons rhythmically active in swimming). All groups of neurons expressed I-NaP, but the currents differed in decay time constants, amplitudes, and the membrane potential at which I-NaP peaked. Low concentrations (1 mu M) of the I-NaP blocker riluzole blocked I-NaP similar to 30% and decreased the excitability of the three neuron groups without affecting spike amplitudes or cellular input resistances. Riluzole reduced the number of rebound spikes in dINs and depressed repetitive firing in RB neurons and non-dINs. At the behavior level, riluzole at 1 mu M shortened fictive swimming episodes. It also reduced the number of action potentials neurons fired on each struggling cycle. The results show that I-NaP may play important modulatory roles in motor behaviors.NEW & NOTEWORTHY We have characterized persistent sodium currents in three groups of spinal neurons and their role in shaping spiking activity in the Xenopus tadpole. We then attempted to evaluate the role of persistent sodium currents in regulating tadpole swimming and struggling motor outputs by using low concentrations of the persistent sodium current antagonist riluzole.
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| 29. |
- Tamté, Martin, et al.
(författare)
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Systems level neurophysiological state characteristics for drug evaluation in an animal model of levodopa-induced dyskinesia.
- 2016
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 115:3, s. 1713-1729
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Tidskriftsartikel (refereegranskat)abstract
- Disorders affecting the central nervous system have proven particularly hard to treat and disappointingly few of novel therapies have reached the clinics in the last decades. A better understanding of the physiological processes in the brain underlying various symptoms could therefore greatly improve the rate of progress in this field. We here show how systems level descriptions of different brain states reliably can be obtained through a newly developed method based on large-scale recordings in distributed neural networks encompassing several different brain structures. Using this technology we characterize the neurophysiological states associated with parkinsonism and levodopa-induced dyskinesia in a rodent model of Parkinson's disease together with pharmacological interventions aimed at reducing dyskinetic symptoms. Our results show that the obtained electrophysiological data add significant information to conventional behavioral evaluations and hereby elucidates the underlying effects of treatments in greater detail. Taken together, these results potentially open up for studies of neurophysiological mechanisms underlying symptoms in a wide range of neurologic and psychiatric conditions that until now have been very hard to investigate in animal models of disease.
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| 30. |
- Thomas, Christine K, et al.
(författare)
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Increases in human motoneuron excitability after cervical spinal cord injury depend on the level of injury
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 117:2, s. 684-691
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Tidskriftsartikel (refereegranskat)abstract
- After human spinal cord injury (SCI), motoneuron recruitment and firing rate during voluntary and involuntary contractions may be altered by changes in motoneuron excitability. Our aim was to compare F-waves in single thenar motor units paralyzed by cervical SCI to those in uninjured controls because at the single unit level, F-waves primarily reflect the intrinsic properties of the motoneuron and its initial segment. With intraneural motor axon stimulation, F-waves were evident in all four participants with C4-level SCI, absent in eight with C5 or C6 injury, and present in six of 12 Uninjured participants (p<0.001). The percentage of units that generated F-waves differed across groups (C4: 30%; C5 or C6: 0%; Uninjured: 16%; p<0.001). Mean (± SD) proximal axon conduction velocity was slower after C4 SCI (64±4 m/s, n=6 units; Uninjured: 73±8 m/s, n=7 units, p=0.037). Mean distal axon conduction velocity differed by group (C4: 40±8 m/s, n=20 units; C5 or C6: 49±9 m/s, n=28; Uninjured: 60±7 m/s, n=45; p<0.001). Motor unit properties (EMG amplitude, twitch force) only differed after SCI, not by injury level (p≤0.004). Motor units with F-waves had distal conduction velocities, M-wave amplitudes, and twitch forces that spanned the respective group range, indicating that units with heterogeneous properties produced F-waves. Recording unitary F-waves has shown that thenar motoneurons closer to the SCI (C5 or C6) have reduced excitability, whereas those further away (C4) have increased excitability, which may exacerbate muscle spasms. This difference in motoneuron excitability may be related to the extent of membrane depolarization following SCI.
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| 31. |
- Vallbo, Åke, 1933
(författare)
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Microneurography: how it started and how it works
- 2018
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 120:3, s. 1415-1427
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Tidskriftsartikel (refereegranskat)abstract
- In the first section, this historical review describes endeavors to develop the method for recording normal nerve impulse traffic in humans, designated microneurography. The method was developed at the Department of Clinical Neurophysiology of the Academic Hospital in Uppsala, Sweden. Microneurography involves the impalement of a peripheral nerve with a tungsten needle electrode. Electrode position is adjusted by hand until the activity of interest is discriminated. Nothing similar had previously been tried in animal preparations, and thus the large number of preceding studies that recorded afferent activity in other mammals did not offer pertinent methodological guidance. For 2 years, the two scientists involved in the research impaled their own nerves with electrodes to test various kinds of needles and explore different neural systems, all the while carefully watching for signs of nerve damage. Temporary paresthesiae were common, whereas enduring sequelae never followed. Single-unit impulse trains could be discriminated, even those originating from unmyelinated fibers. An explanation for the discrimination of unitary impulses using a coarse electrode is inferred based on the electrical characteristics of the electrode placed in the flesh and the impulse shapes, as discussed in the second section of this paper. Microneurography and the microstimulation of single afferents, combined with psychophysical methods and behavioral tests, have generated new knowledge particularly regarding four neural systems, namely the proprioceptive system, the cutaneous mechanoreceptive system, the cutaneous nociceptive system, and the sympathetic efferent system to skin structures and muscular blood vessels. Examples of achievements based on microneurography are presented in the final section.
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| 32. |
- Vemula, MG, et al.
(författare)
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Kinematics of forward and backward locomotion performed in different environmental conditions
- 2019
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 122:5, s. 2142-2155
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Tidskriftsartikel (refereegranskat)abstract
- Mice are frequently used in analyses of the locomotor system. Although forward locomotion (FWL) in intact mice has been studied previously, backward locomotion (BWL) in mice has never been analyzed. The aim of the present study was to compare kinematics of FWL and BWL performed in different environmental conditions (i.e., in a tunnel, on a treadmill, and on an air-ball). In all setups, the average speed and step amplitude during BWL were significantly reduced compared with FWL. The cycle duration varied greatly during both FWL and BWL. The average swing duration during BWL was twice shorter than during FWL on each setup. Mice exhibited different interlimb coordinations (trot and walk with lateral or diagonal sequence) during BWL but only one gait (walk with lateral sequence) during FWL. Location of the rostro-caudal paw trajectory in relation to the hip projection to the surface (HP) depended on hip height. With low hip height, the trajectory was displaced either rostrally (anterior steps) or caudally (posterior steps) to HP. With high hip height, HP was near the middle of the trajectory (middle steps). During FWL, all three forms of steps were observed in the tunnel and predominantly anterior and posterior steps on the treadmill and air-ball, respectively. During BWL, only anterior steps were observed. Intralimb coordination depended on the form of stepping. Limb joints were coordinated to keep the hip at approximately constant height during stance and to have the smallest functional limb length during swing when the limb passed under the hip.NEW & NOTEWORTHY Mice are extensively used for the analysis of the locomotor system. This study is the first examination of the kinematics of forward and backward locomotor movements in different environmental conditions in mice. Obtained results represent a benchmark for studies based on manipulations of activity of specific populations of neurons to reveal their roles in control of specific aspects of locomotion.
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| 33. |
- Watkins, Roger H., 1988, et al.
(författare)
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Optimal delineation of single C-tactile and C-nociceptive afferents in humans by latency slowing
- 2017
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 117:4, s. 1608-1614
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Tidskriftsartikel (refereegranskat)abstract
- C-mechanoreceptors in humans comprise a population of unmyelinated afferents exhibiting a wide range of mechanical sensitivities. C-mechanoreceptors are putatively divided into those signaling gentle touch (C-tactile afferents, CTs) and nociception (C-mechanosensitive nociceptors, CMs), giving rise to positive and negative affect, respectively. We sought to distinguish, compare, and contrast the properties of a population of human C-mechanoreceptors to see how fundamental the divisions between these putative subpopulations are. We used microneurography to record from individual afferents in humans and applied electrical and mechanical stimulation to their receptive fields. We show that C-mechanoreceptors can be distinguished unequivocally into two putative populations, comprising CTs and CMs, by electrically evoked spike latency changes (slowing). After both natural mechanical stimulation and repetitive electrical stimulation there was markedly less latency slowing in CTs compared with CMs. Electrical receptive field stimulation, which bypasses the receptor end organ, was most effective in classifying C-mechanoreceptors, as responses to mechanical receptive field stimulation overlapped somewhat, which may lead to misclassification. Furthermore, we report a subclass of low-threshold CM responding to gentle mechanical stimulation and a potential subclass of CT afferent displaying burst firing. We show that substantial differences exist in the mechanisms governing axonal conduction between CTs and CMs. We provide clear electrophysiological "signatures" (extent of latency slowing) that can be used in unequivocally identifying populations of C-mechanoreceptors in single-unit and multiunit microneurography studies and in translational animal research into affective touch. Additionally, these differential mechanisms may be pharmacologically targetable for separate modulation of positive and negative affective touch information. NEW & NOTEWORTHY Human skin encodes a plethora of touch interactions, and affective tactile information is primarily signaled by slowly conducting C-mechanoreceptive afferents. We show that electrical stimulation of low-threshold C-tactile afferents produces markedly different patterns of activity compared with high-threshold C-mechanoreceptive nociceptors, although the populations overlap in their responses to mechanical stimulation. This fundamental distinction demonstrates a divergence in affective touch signaling from the first stage of sensory processing, having implications for the processing of interpersonal touch.
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| 34. |
- Weiler, Jeffrey, et al.
(författare)
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Coordinating long-latency stretch responses across the shoulder, elbow, and wrist during goal-directed reaching
- 2016
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 116:5, s. 2236-2249
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Tidskriftsartikel (refereegranskat)abstract
- The long-latency stretch response (muscle activity 50-100 ms after a mechanical perturbation) can be coordinated across multiple joints to support goal-directed actions. Here we assessed the flexibility of such coordination and whether it serves to counteract intersegmental dynamics and exploit kinematic redundancy. In three experiments, participants made planar reaches to visual targets after elbow perturbations and we assessed the coordination of long-latency stretch responses across shoulder, elbow, and wrist muscles. Importantly, targets were placed such that elbow and wrist (but not shoulder) rotations could help transport the hand to the target-a simple form of kinematic redundancy. In experiment 1 we applied perturbations of different magnitudes to the elbow and found that long-latency stretch responses in shoulder, elbow, and wrist muscles scaled with perturbation magnitude. In experiment 2 we examined the trial-by-trial relationship between long-latency stretch responses at adjacent joints and found that the magnitudes of the responses in shoulder and elbow muscles, as well as elbow and wrist muscles, were positively correlated. In experiment 3 we explicitly instructed participants how to use their wrist to move their hand to the target after the perturbation. We found that long-latency stretch responses in wrist muscles were not sensitive to our instructions, despite the fact that participants incorporated these instructions into their voluntary behavior. Taken together, our results indicate that, during reaching, the coordination of long-latency stretch responses across multiple joints counteracts intersegmental dynamics but may not be able to exploit kinematic redundancy.
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| 35. |
- Zeberg, H, et al.
(författare)
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Density of voltage-gated potassium channels is a bifurcation parameter in pyramidal neurons
- 2015
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 113:2, s. 537-549
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Tidskriftsartikel (refereegranskat)abstract
- Several types of intrinsic dynamics have been identified in brain neurons. Type 1 excitability is characterized by a continuous frequency-stimulus relationship and, thus, an arbitrarily low frequency at threshold current. Conversely, Type 2 excitability is characterized by a discontinuous frequency-stimulus relationship and a nonzero threshold frequency. In previous theoretical work we showed that the density of Kv channels is a bifurcation parameter, such that increasing the Kv channel density in a neuron model transforms Type 1 excitability into Type 2 excitability. Here we test this finding experimentally, using the dynamic clamp technique on Type 1 pyramidal cells in rat cortex. We found that increasing the density of slow Kv channels leads to a shift from Type 1 to Type 2 threshold dynamics, i.e., a distinct onset frequency, subthreshold oscillations, and reduced latency to first spike. In addition, the action potential was resculptured, with a narrower spike width and more pronounced afterhyperpolarization. All changes could be captured with a two-dimensional model. It may seem paradoxical that an increase in slow K channel density can lead to a higher threshold firing frequency; however, this can be explained in terms of bifurcation theory. In contrast to previous work, we argue that an increased outward current leads to a change in dynamics in these neurons without a rectification of the current-voltage curve. These results demonstrate that the behavior of neurons is determined by the global interactions of their dynamical elements and not necessarily simply by individual types of ion channels.
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