| 1. |
- Hudson, Lawrence N, et al.
(författare)
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The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
- 2017
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
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Tidskriftsartikel (refereegranskat)abstract
- The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
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| 2. |
- Bergmeister, Konstantin D., et al.
(författare)
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Broadband prosthetic interfaces: Combining nerve transfers and implantable multichannel EMG technology to decode spinal motor neuron activity
- 2017
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Ingår i: Frontiers in Neuroscience. - : Frontiers Media SA. - 1662-4548 .- 1662-453X. ; 11, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Modern robotic hands/upper limbs may replace multiple degrees of freedom of extremity function. However, their intuitive use requires a high number of control signals, which current man-machine interfaces do not provide. Here, we discuss a broadband control interface that combines targeted muscle reinnervation, implantable multichannel electromyographic sensors, and advanced decoding to address the increasing capabilities of modern robotic limbs. With targeted muscle reinnervation, nerves that have lost their targets due to an amputation are surgically transferred to residual stump muscles to increase the number of intuitive prosthetic control signals. This surgery re-establishes a nerve-muscle connection that is used for sensing nerve activity with myoelectric interfaces. Moreover, the nerve transfer determines neurophysiological effects, such as muscular hyper-reinnervation and cortical reafferentation that can be exploited by the myoelectric interface. Modern implantable multichannel EMG sensors provide signals from which it is possible to disentangle the behavior of single motor neurons. Recent studies have shown that the neural drive to muscles can be decoded from these signals and thereby the user's intention can be reliably estimated. By combining these concepts in chronic implants and embedded electronics, we believe that it is in principle possible to establish a broadband man-machine interface, with specific applications in prosthesis control. This perspective illustrates this concept, based on combining advanced surgical techniques with recording hardware and processing algorithms. Here we describe the scientific evidence for this concept, current state of investigations, challenges, and alternative approaches to improve current prosthetic interfaces.
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| 3. |
- Bergmeister, Konstantin D, et al.
(författare)
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Peripheral nerve transfers change target muscle structure and function
- 2019
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Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Selective nerve transfers surgically rewire motor neurons and are used in extremity reconstruction to restore muscle function or to facilitate intuitive prosthetic control. We investigated the neurophysiological effects of rewiring motor axons originating from spinal motor neuron pools into target muscles with lower innervation ratio in a rat model. Following reinnervation, the target muscle's force regenerated almost completely, with the motor unit population increasing to 116% in functional and 172% in histological assessments with subsequently smaller muscle units. Muscle fiber type populations transformed into the donor nerve's original muscles. We thus demonstrate that axons of alternative spinal origin can hyper-reinnervate target muscles without loss of muscle force regeneration, but with a donor-specific shift in muscle fiber type. These results explain the excellent clinical outcomes following nerve transfers in neuromuscular reconstruction. They indicate that reinnervated muscles can provide an accurate bioscreen to display neural information of lost body parts for high-fidelity prosthetic control.
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| 4. |
- Dideriksen, Jakob L., et al.
(författare)
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Electrical stimulation of afferent pathways for the suppression of pathological tremor
- 2017
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Ingår i: Frontiers in Neuroscience. - : Frontiers Media SA. - 1662-4548 .- 1662-453X. ; 11, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Pathological tremors are involuntary oscillatory movements which cannot be fully attenuated using conventional treatments. For this reason, several studies have investigated the use of neuromuscular electrical stimulation for tremor suppression. In a recent study, however, we found that electrical stimulation below the motor threshold also suppressed tremor, indicating involvement of afferent pathways. In this study, we further explored this possibility by systematically investigating how tremor suppression by afferent stimulation depends on the stimulation settings. In this way, we aimed at identifying the optimal stimulation strategy, as well as to elucidate the underlying physiological mechanisms of tremor suppression. Stimulation strategies varying the stimulation intensity and pulse timing were tested in nine tremor patients using either intramuscular or surface stimulation. Significant tremor suppression was observed in six patients (tremor suppression > 75% was observed in three patients) and the average optimal suppression level observed across all subjects was 52%. The efficiency for each stimulation setting, however, varied substantially across patients and it was not possible to identify a single set of stimulation parameters that yielded positive results in all patients. For example, tremor suppression was achieved both with stimulation delivered in an out-of-phase pattern with respect to the tremor, and with random timing of the stimulation. Overall, these results indicate that low-current stimulation of afferent fibers is a promising approach for tremor suppression, but that further research is required to identify how the effect can be maximized in the individual patient.
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| 5. |
- Dideriksen, Jakob L., et al.
(författare)
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Physiological recruitment of motor units by high-frequency electrical stimulation of afferent pathways
- 2015
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 118:3, s. 365-376
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Tidskriftsartikel (refereegranskat)abstract
- Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation, but electrically evoked muscle activation is in several ways different from voluntary muscle contractions. These differences lead to challenges in the use of NMES for restoring muscle function. We investigated the use of low-current, high-frequency nerve stimulation to activate the muscle via the spinal motoneuron (MN) pool to achieve more natural activation patterns. Using a novel stimulation protocol, the H-reflex responses to individual stimuli in a train of stimulation pulses at 100 Hz were reliably estimated with surface EMG during low-level contractions. Furthermore, single motor unit recruitment by afferent stimulation was analyzed with intramuscular EMG. The results showed that substantially elevated H-reflex responses were obtained during 100-Hz stimulation with respect to a lower stimulation frequency. Furthermore, motor unit recruitment using 100-Hz stimulation was not fully synchronized, as it occurs in classic NMES, and the discharge rates differed among motor units because each unit was activated only after a specific number of stimuli. The most likely mechanism behind these observations is the temporal summation of subthreshold excitatory postsynaptic potentials from Ia fibers to the MNs. These findings and their interpretation were also verified by a realistic simulation model of afferent stimulation of a MN population. These results suggest that the proposed stimulation strategy may allow generation of considerable levels of muscle activation by
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| 6. |
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| 7. |
- Farina, Dario, et al.
(författare)
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Principles of motor unit physiology evolve with advances in technology
- 2016
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Ingår i: Physiology. - : American Physiological Society. - 1548-9213 .- 1548-9221. ; 31:2, s. 83-94
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Forskningsöversikt (refereegranskat)abstract
- Movements are generated by the coordinated activation of motor units. Recent technological advances have made it possible to identify the concurrent activity of several tens of motor units, in contrast with much smaller samples available in classic studies. We discuss how these advances in technology have enabled the development of a population perspective of how the central nervous system controls motor unit activity and thereby the forces exerted by muscles. Movements are controlled by the coordinated activation of neuromuscular units that produce force: the motor units (28, 48). Each motor unit comprises a motoneuron and a muscle unit, where the latter refers to the muscle fibers innervated by the motoneuron. The nervous system produces movements by delivering synaptic inputs to motoneurons that innervate at least several muscles. Once activated, the motoneurons engage the muscle units in the involved muscles to produce both synergistic and antagonistic muscle forces. To perform movements accurately, the neural drive to muscles (the ensemble output of motoneurons) transmitted by motoneurons from supraspinal centers and sensory receptors must be reliable. As a first approximation, motoneurons process synaptic inputs by functioning as integrate-and-fire systems (66), which means that motoneurons are activated when the time integral of the synaptic inputs causes a change in membrane potential that exceeds the voltage threshold of the motoneuron. The muscle force at which this occurs is known as the recruitment threshold of the motor unit. The rate at which motoneurons discharge action potentials is positively associated with the difference between the synaptic input received by the motoneuron and its voltage threshold. Modulation of discharge rate is known as rate coding (48). Motor units transduce the neural activation signal into muscle forces, which means that the discharge characteristics of motor units contain information about the neural control signal. It is for this reason that methods were developed to record and decode the discharge characteristics of motor units with intramuscular electrodes (1, 28). One feature of such methods is the high selectivity of the recording, which ensures signal detection but limits the number of motor units that can be discriminated concurrently. Recent developments in electrode technology and biological signal processing have greatly reduced this limitation by making it possible to monitor the concurrent activity of many motor units (85). The concurrent recordings and computational modeling have enabled the development of a population perspective of how the nervous system controls movement. Several key findings indicate that classic concepts of motor unit function derived from recording the activity of only a few motor units need to be revised. The aim of the current review is to describe the influence of recent advances in technology on our current understanding of how the nervous system controls motor unit activity and thereby the forces exerted by muscles.
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| 8. |
- Karimimehr, Saeed, et al.
(författare)
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A real-time method for decoding the neural drive to muscles using single-channel intra-muscular EMG recordings
- 2017
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Ingår i: International Journal of Neural Systems. - 0129-0657. ; 27:6
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Tidskriftsartikel (refereegranskat)abstract
- The neural command from motor neurons to muscles — sometimes referred to as the neural drive to muscle — can be identified by decomposition of electromyographic (EMG) signals. This approach can be used for inferring the voluntary commands in neural interfaces in patients with limb amputations. This paper proposes for the first time an innovative method for fully automatic and real-time intramuscular EMG (iEMG) decomposition. The method is based on online single-pass density-based clustering and adaptive classification of bivariate features, using the concept of potential measure. No attempt was made to resolve superimposed motor unit action potentials. The proposed algorithm was validated on sets of simulated and experimental iEMG signals. Signals were recorded from the biceps femoris long-head, vastus medialis and lateralis and tibialis anterior muscles during low-to-moderate isometric constant-force and linearly-varying force contractions. The average number of missed, duplicated and erroneous clusters for the examined signals was 0.5±0.80.5±0.8, 1.2±1.01.2±1.0, and 1.0±0.81.0±0.8, respectively. The average decomposition accuracy (defined similar to signal detection theory but without using True Negatives in the denominator) and coefficient of determination (variance accounted for) for the cumulative discharge rate estimation were 70±9%70±9%, and 94±5%94±5%, respectively. The time cost for processing each 200ms iEMG interval was 43±1643±16 (21–97)ms. However, computational time generally increases over time as a function of frames/signal epochs. Meanwhile, the incremental accuracy defined as the accuracy of real-time analysis of each signal epoch, was 74±1874±18% for epochs recorded after initial one second. The proposed algorithm is thus a promising new tool for neural decoding in the next-generation of prosthetic control.
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| 9. |
- Luu, Billy L., et al.
(författare)
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Motor unit territories in human genioglossus estimated with multichannel intramuscular electrodes
- 2018
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 124:3, s. 664-671
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Tidskriftsartikel (refereegranskat)abstract
- The discharge patterns of genioglossus motor units during breathing have been well-characterized in previous studies, but their localization and territories are not known. In this study, we used two newly developed intramuscular multichannel electrodes to estimate the territories of genioglossus motor units in the anterior and posterior regions of the muscle. Seven healthy men participated. Each electrode contained fifteen bipolar channels, separated by 1 mm, and was inserted percutaneously below the chin, perpendicular to the skin, to a depth of 36 mm. Single motor unit activity was recorded with subjects awake, supine, and breathing quietly through a nasal mask for 180 s. Motor unit territories were estimated from the spike-triggered averages of the electromyographic signal from each channel. A total of 30 motor units were identified: 22 expiratory tonic, 1 expiratory phasic, 2 tonic, 3 inspiratory tonic, and 2 inspiratory phasic. Motor units appeared to be clustered based on unit type, with peak activities for expiratory units predominantly located in the anterior and superficial fibers of genioglossus and inspiratory units in the posterior region. Of these motor unit types, expiratory tonic units had the largest estimated territory, a mean 11.3 mm (SD 1.9). Estimated territories of inspiratory motor units ranged from 3 to 6 mm. In accordance with the distribution of motor unit types, the estimated territory of genioglossus motor units varied along the sagittal plane, decreasing from anterior to posterior. Our findings suggest that genioglossus motor units have large territories relative to the cross-sectional size of the muscle. NEW&NOTEWORTHY In this study, we used a new multichannel intramuscular electrode to address a fundamental property of human genioglossus motor units. We describe the territory of genioglossus motor units in the anterior and posterior regions of the muscle and show a decrease in territory size from anterior to posterior and that expiratory-related motor units have larger estimated territories than inspiratory-related motor units.
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| 10. |
- Muceli, Silvia, 1981, et al.
(författare)
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A thin-film multichannel electrode for muscle recording and stimulation in neuroprosthetics applications
- 2019
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Ingår i: Journal of Neural Engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 16:2
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Tidskriftsartikel (refereegranskat)abstract
- Objective. We propose, design and test a novel thin-film multichannel electrode that can be used for both recording from and stimulating a muscle in acute implants. Approach. The system is built on a substrate of polyimide and contains 12 recording and three stimulation sites made of platinum. The structure is 420 µm wide, 20 µm thick and embeds the recording and stimulation contacts on the two sides of the polyimide over an approximate length of 2 cm. We show representative applications in healthy individuals as well as tremor patients. The designed system was tested by a psychometric characterization of the stimulation contacts in six tremor patients and three healthy individuals determining the perception threshold and current limit as well as the success rate in discriminating elicited sensations (electrotactile feedback). Also, we investigated the possibility of using the intramuscular electrode for reducing tremor in one patient by electrical stimulation delivered with timing based on the electromyographic activity recorded with the same electrode. Main results. In the tremor patients, the current corresponding to the perception threshold and the current limit were 0.7 ± 0.2 and 1.4 ± 0.7 mA for the wrist flexor muscles and 0.4 ± 0.2 and 1.5 ± 0.7 mA for the extensors. In one patient, closed-loop stimulation resulted in a decrease of the tremor power >50%. In healthy individuals the perception threshold and current limits were 0.9 ± 0.6 and 2.1 ± 0.6 mA for the extensor carpi radialis muscle. The subjects could distinguish four or six stimulation patterns (two or three stimulation sites × two stimulation current amplitudes) with true positive rate >80% (two subjects) and >60% (one subject), respectively. Significance. The proposed electrode provides a compact multichannel interface for recording electromyogram and delivering electrical stimulation in applications such as neuroprostheses for tremor suppression and closed-loop myoelectric prostheses.
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