| 1. |
- Ng, Kevin, et al.
(author)
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Human Foot Outperforms the Hand in Mechanical Pain Discrimination
- 2024
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In: eNeuro. - : SOC NEUROSCIENCE. - 2373-2822. ; 11:2
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Journal article (peer-reviewed)abstract
- Tactile discrimination has been extensively studied, but mechanical pain discrimination remains poorly characterized. Here, we measured the capacity for mechanical pain discrimination using a two-alternative forced choice paradigm, with force-calibrated indentation stimuli (Semmes-Weinstein monofilaments) applied to the hand and foot dorsa of healthy human volunteers. In order to characterize the relationship between peripheral nociceptor activity and pain perception, we recorded single-unit activity from myelinated (A) and unmyelinated (C) mechanosensitive nociceptors in the skin using microneurography. At the perceptual level, we found that the foot was better at discriminating noxious forces than the hand, which stands in contrast to that for innocuous force discrimination, where the hand performed better than the foot. This observation of superior mechanical pain discrimination on the foot compared to the hand could not be explained by the responsiveness of individual nociceptors. We found no significant difference in the discrimination performance of either the myelinated or unmyelinated class of nociceptors between skin regions. This suggests the possibility that other factors such as skin biophysics, receptor density or central mechanisms may underlie these regional differences.
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| 2. |
- Svantesson, Mats, 1975-
(author)
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Self-supervised deep learning and EEG categorization
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Deep learning has the potential to be used to improve and streamline EEG analysis. At the present, classifiers and supervised learning dominate the field. Supervised learning depends on target labels which most often are created by human experts manually classifying data. A problem with supervised learning is intra- and interrater agreement which in some instances are far from perfect. This can affect the training and make evaluation more difficult. This thesis includes three papers where self-supervised deep neural networks were developed. In self-supervised learning, the input data to the networks themselves contain structures that are used as targets for the training and no labeling is necessary. In paper I, deep neural networks were trained to increase the number of-, or to recreate missing EEG-channels. The performance was at least on the same level as that of spherical interpolation, but unlike in the case of interpolation, missing data does not have to be identified manually first. Papers II and III involved developing deep neural networks for clustering analysis. The networks produced two-dimensional representations of EEG data and the training strategy was based on the principle of t-distributed stochastic neighbor embedding (t-SNE). In paper II, comparisons were made to parametric t-SNE and EEG-features obtained from time-frequency methods. The deep neural networks produced more distinct clustering when tested on data annotated for epileptiform discharges, seizure activity, or sleep-wakefulness.In paper III, the newly developed method was used to compare annotations of epileptiform discharges. Two experts performed independent annotations and classifiers were trained on these, using supervised learning, which in turn produced new annotations. The agreement when comparing two sets of annotations was not larger between the two experts than between an expert and a classifier. The analysis showed that differences in the annotations by the experts influenced the training of the classifiers. However, the clustering analysis indicated that although it was not always the exact same waveforms that were assessed as epileptiform discharges, they were often similar.The work thus resulted in different methods to process and analyze EEG data, which may have practical usefulness. Traditional agreement scores only assess the exact agreement. However, they reveal nothing about the nature of disagreement. Cluster analysis can provide a means to perform this assessment.
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| 3. |
- Rådman, Lisa, 1983-, et al.
(author)
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Hand function after an electrical accident : a case-control study
- 2023
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In: Journal of Occupational and Environmental Medicine. - : Lippincott Williams & Wilkins. - 1076-2752 .- 1536-5948. ; 65:3, s. 242-248
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Journal article (peer-reviewed)abstract
- OBJECTIVE: Electrical accidents cause both acute and long-term injuries. The care of acute injuries is somewhat standardized, but currently recommendations or assessment tools are not available for assessing the long-term effects of an accident on hand function.METHODS: A case-control study of 24 healthy controls and 24 cases, 1-5 years after an electrical accident and with self-reported neurosensory symptoms, was performed using three hand-function tests: the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire, the Purdue Pegboard test and the Shape and Identification (STI) test.RESULTS: Compared to the control group, patients received statistically significantly lower scores for the DASH outcome measure and the Purdue Pegboard and for one finger on the STI test.CONCLUSION: Hand function is affected after an electrical accident in individuals with self-reported neurosensory symptoms.
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| 4. |
- Savallampi, Mattias, et al.
(author)
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Social Touch Reduces Pain Perception-An fMRI Study of Cortical Mechanisms
- 2023
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In: Brain Sciences. - : MDPI. - 2076-3425 .- 2076-3425. ; 13:3
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Journal article (peer-reviewed)abstract
- Unmyelinated low-threshold mechanoreceptors (C-tactile, CT) in the human skin are important for signaling information about hedonic aspects of touch. We have previously reported that CT-targeted brush stroking by means of a robot reduces experimental mechanical pain. To improve the ecological validity of the stimulation, we developed standardized human-human touch gestures for signaling attention and calming. The attention gesture is characterized by tapping of the skin and is perceived as neither pleasant nor unpleasant, i.e., neutral. The calming gesture is characterized by slow stroking of the skin and is perceived as moderately to very pleasant. Furthermore, the attention (tapping) gesture is ineffective, whereas the calming (stroking) gesture is effective in activating CT-afferents. We conducted an fMRI study (n = 32) and capitalized on the previous development of touch gestures. We also developed an MR compatible stimulator for high-precision mechanical pain stimulation of the thenar region of the hand. Skin-to-skin touching (stroking or tapping) was applied and was followed by low and high pain. When the stroking gesture preceded pain, the pain was rated as less intense. When the tapping gesture preceded the pain, the pain was rated as more intense. Individual pain perception related to insula activation, but the activation was not higher for stroking than for tapping in any brain area during the stimulation period. However, during the evaluation period, stronger activation in the periaqueductal gray matter was observed after calming touch compared to after tapping touch. This finding invites speculation that human-human gentle skin stroking, effective in activating CT-afferents, reduced pain through neural processes involving CT-afferents and the descending pain pathway.
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| 5. |
- Svantesson, Mats, 1975-, et al.
(author)
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Get a New Perspective on EEG: Convolutional Neural Network Encoders for Parametric t-SNE
- 2023
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In: Brain Sciences. - : MDPI. - 2076-3425 .- 2076-3425. ; 13:3
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Journal article (peer-reviewed)abstract
- t-distributed stochastic neighbor embedding (t-SNE) is a method for reducing high-dimensional data to a low-dimensional representation, and is mostly used for visualizing data. In parametric t-SNE, a neural network learns to reproduce this mapping. When used for EEG analysis, the data are usually first transformed into a set of features, but it is not known which features are optimal. The principle of t-SNE was used to train convolutional neural network (CNN) encoders to learn to produce both a high- and a low-dimensional representation, eliminating the need for feature engineering. To evaluate the method, the Temple University EEG Corpus was used to create three datasets with distinct EEG characters: (1) wakefulness and sleep; (2) interictal epileptiform discharges; and (3) seizure activity. The CNN encoders produced low-dimensional representations of the datasets with a structure that conformed well to the EEG characters and generalized to new data. Compared to parametric t-SNE for either a short-time Fourier transform or wavelet representation of the datasets, the developed CNN encoders performed equally well in separating categories, as assessed by support vector machines. The CNN encoders generally produced a higher degree of clustering, both visually and in the number of clusters detected by k-means clustering. The developed principle is promising and could be further developed to create general tools for exploring relations in EEG data.
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| 6. |
- Thorell, Oumie, et al.
(author)
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Investigations into an overlooked early component of painful nociceptive withdrawal reflex responses in humans
- 2023
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In: Frontiers in Pain Research. - : FRONTIERS MEDIA SA. - 2673-561X. ; 3
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Journal article (peer-reviewed)abstract
- Introduction: The role of pain as a warning system necessitates a rapid transmission of information from the periphery for the execution of appropriate motor responses. The nociceptive withdrawal reflex (NWR) is a physiological response to protect the limb from a painful stimulus and is often considered an objective measure of spinal nociceptive excitability. The NWR is commonly defined by its latency in the presumed Aδ-fiber range consistent with the canonical view that "fast pain" is signaled by Aδ nociceptors. We recently demonstrated that human skin is equipped with ultrafast (Aβ range) nociceptors. Here, we investigated the short-latency component of the reflex and explored the relationship between reflex latency and pain perception.Methods: We revisited our earlier work on NWR measurements in which, following convention, only reflex responses in the presumed Aδ range were considered. In our current analysis, we expanded the time window to search for shorter latency responses and compared those with pain ratings.Results: In both cohorts, we found an abundance of recordings with short-latency reflex responses. In nearly 90% of successful recordings, only single reflex responses (not dual) were seen which allowed us to compare pain ratings based on reflex latencies. We found that shorter latency reflexes were just as painful as those in the conventional latency range.Conclusion: We found a preponderance of short-latency painful reflex responses. Based on this finding, we suggest that short-latency responses must be considered in future studies. Whether these are signaled by the ultrafast nociceptors remains to be determined.
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| 7. |
- Böhme, Rebecca, et al.
(author)
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Differentiating self-touch from social touch
- 2022
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In: CURRENT OPINION IN BEHAVIORAL SCIENCES. - : ELSEVIER. - 2352-1546. ; 43, s. 27-33
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Journal article (peer-reviewed)abstract
- Humans need to be able to differentiate between signals they produce themselves and signals that arise from non-self-causes. It has long been discussed that the brain uses a copy of the motor command, an efference copy, to predict the sensory outcomes of ones own action - and to attenuate these. While studies in humans suggest that cerebellum and supplementary motor area play crucial roles in the attenuation, a study in mice suggests a global suppression during self-touch. However, the sensory percepts of self-touch are not fully cancelled out. Humans touch themselves frequently suggesting a behavioral relevance of self-touch, as to refocus attention, to calm oneself down during stress, to itch or for self-enjoyment. We discuss studies on sensory attenuation as well as the behavioral relevance of self-touch and open questions for future research.
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| 8. |
- Frost-Karlsson, Morgan, et al.
(author)
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Neural processing of self-touch and other-touch in anorexia nervosa and autism spectrum condition
- 2022
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In: NeuroImage. - : Elsevier Science Ltd. - 2213-1582. ; 36
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Journal article (peer-reviewed)abstract
- Introduction: The tactile sense plays a crucial role in the development and maintenance of a functional bodily self. The ability to differentiate between self-and nonself-generated touch contributes to the perception of the bodies boundaries and more generally to self-other-distinction, both of which are thought be altered in anorexia nervosa (AN) and autism spectrum condition (AS). While it has been suggested that AN and AS are characterized by overlapping symptomatology, they might differ regarding body perception and self-other-distinction. Methods: Participants with a diagnosis of AN (n = 25), AS (n = 29), and a comparison group without diagnoses (n = 57) performed a self-other-touch task during functional brain imaging. In the experimental conditions, they stroked their own arm or were stroked on the arm by an experimenter. Results: As shown previously, the CG group showed lower activation or deactivation in response to self-touch compared to social touch from someone else. A main group effect was found in areas including somatosensory cortex, frontal and temporal gyri, insula, and subcortical regions. This was driven by increased activations in participants with AN, while participants in the AS group showed mostly comparable activations to the com-parison group. Conclusions: AN diagnosis was associated with an increased neural activity in response to both self-touch and social touch. Failure to attenuate self-touch might relate to altered predictions regarding the own body and reduced perception of bodily boundaries. Participants with an AS diagnosis were mostly comparable to the comparison group, potentially indicating unaltered tactile self-other-distinction.
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| 9. |
- Löken, Line Sofie, 1977, et al.
(author)
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A topographical and physiological exploration of C-tactile afferents and their response to menthol and histamine
- 2022
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In: Journal of Neurophysiology. - : AMER PHYSIOLOGICAL SOC. - 0022-3077 .- 1522-1598. ; 127:2, s. 463-473
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Journal article (peer-reviewed)abstract
- Unmyelinated tactile (C-tactile or CT) afferents are abundant in arm hairy skin and have been suggested to signal features of soda) affective touch. Here, we recorded from unmyelinated low-threshold mechanosensitive afferents in the peroneal and radial nerves. The most distal receptive fields were located on the proximal phalanx of the third finger for the superficial branch of the radial nerve and near the lateral malleolus for the peroneal nerve. We found that the physiological properties with regard to conduction velocity and mechanical threshold, as well as their tuning to brush velocity, were similar in CT units across the antebrachial (n = 27), radial (n = 8), and peroneal (n = 4) nerves. Moreover, we found that although CT afferents are readily found during microneurography of the arm nerves, they appear to be much more sparse in the lower leg compared with C-nociceptors. We continued to explore CT afferents with regard to their chemical sensitivity and found that they could not be activated by topical application to their receptive field of either the cooling agent menthol or the pruritogen histamine. In light of previous studies showing the combined effects that temperature and mechanical stimuli have on these neurons, these findings add to the growing body of research suggesting that CT afferents constitute a unique class of sensory afferents with highly specialized mechanisms for transducing gentle touch. NEW & NOTEWORHY Unmyelinated tactile (CT) afferents are abundant in arm hairy skin and are thought to signal features of social affective touch. We show that CTs are also present but are relatively sparse in the lower leg compared with C-nociceptors. CTs display similar physiological properties across the arm and leg nerves. Furthermore, CT afferents do not respond to the cooling agent menthol or the pruritogen histamine, and their mechanical response properties are not altered by these chemicals.
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| 10. |
- Maallo, Anne, et al.
(author)
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Naturalistic stimuli in touch research
- 2022
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In: Current Opinion in Neurobiology. - : Elsevier Ltd. * Current Opinion Journals. - 0959-4388 .- 1873-6882. ; 75
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Journal article (peer-reviewed)abstract
- Neural mechanisms of touch are typically studied in laboratory settings using robotic or other types of well-controlled devices. Such stimuli are very different from highly complex naturalistic human-to-human touch interactions. The lack of scientifically useful naturalistic stimuli hampers progress, particularly in social touch research. Vision science, on the other hand, has benefitted from inventions such as virtual reality systems that have provided researchers with precision control of naturalistic stimuli. In the field of touch research, producing and manipulating stimuli is particularly challenging due to the complexity of skin mechanics. Here, we review the history of touch neuroscience focusing on the contrast between strictly controlled and naturalistic stimuli, and compare the field to vision science. We discuss new methods that may overcome obstacles with precision-controlled tactile stimuli, and recent successes in naturalistic texture production. In social touch research, precise tracking and measurement of naturalistic human-to-human touch interactions offer exciting new possibilities.
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