Interpersonal touch is an important channel of social emotional interaction. How these physical skin-to-skin touch expressions are processed in the peripheral nervous system is not well understood. From microneurography recordings in humans, we evaluated the capacity of six subtypes of cutaneous mechanoreceptive afferents to differentiate human-delivered social touch expressions. Leveraging statistical and classification analyses, we found that single units of multiple mechanoreceptive Aβ subtypes, especially slowly adapting type II (SA-II) and fast adapting hair follicle afferents (HFA), can reliably differentiate social touch expressions at accuracies similar to human recognition. We then identified the most informative firing patterns of SA-II and HFA afferents, which indicate that average durations of 3-4 s of firing provide sufficient discriminative information. Those two subtypes also exhibit robust tolerance to spike-timing shifts of up to 10-20 ms, varying with touch expressions due to their specific firing properties. Greater shifts in spike-timing, however, can change a firing pattern’s envelope to resemble that of another expression and drastically compromise an afferent’s discrimination capacity. Altogether, the findings indicate that SA-II and HFA afferents differentiate the skin contact of social touch at time scales relevant for such interactions, which are 1-2 orders of magnitude longer than those for non-social touch.  

AIMS: We have evaluated long-term weighted mean HbA_1c (wHbA_1c), HbA_1c variability, diabetes duration, and lipid profiles in relation to the development of diabetic peripheral neuropathy (DPN), nephropathy, and retinopathy in childhood-onset type 1 diabetes.

MATERIALS AND METHODS: In a longitudinal cohort study, 49 patients (21 women) with childhood-onset type 1 diabetes were investigated with neurophysiological measurements, blood tests, and clinical examinations after a diabetes duration of 7.7 (±3.3) years (baseline) and followed with repeated examinations for 30.6 (±5.2) years. We calculated wHbA_1c by integrating the area under all HbA_1c values since the diabetes diagnosis. Lipid profiles were analysed in relation to the presence of DPN. Long-term fluctuations of HbA_1c variability were computed as the standard deviation of all HbA_1c measurements. Data regarding the presence of other diabetes complications were retrieved from medical records.

RESULTS: In this follow-up study, 51% (25/49) of the patients fulfilled electrophysiological criteria for DPN. In nerve conduction studies, there was a deterioration in the amplitudes and conduction velocities for the median, peroneal, and sural nerves over time. Patients with DPN had a longer duration of diabetes, higher wHbA_1c, and increased HbA_1c variability. The lowest wHbA_1c value associated with the development of DPN was 62 mmol/mol (7.8%). The presence of albuminuria and retinopathy was positively correlated with the presence of neuropathy.

CONCLUSIONS: More than half of the patients had developed DPN after 30 years. None of the patients who developed DPN had a wHbA_1c of less than 62 mmol/mol (7.8%).

A coherent sense of self is crucial for social functioning and mental health. The N-methyl-D-aspartate antagonist ketamine induces short-term dissociative experiences and has therefore been used to model an altered state of self-perception. This randomized double-blind placebo-controlled cross-over study investigated the mechanisms for ketamine's effects on the bodily sense of self in the context of affective touch. Thirty healthy participants (15 females/15 males, age 19-39) received intravenous ketamine or placebo while performing self-touch and receiving touch by someone else during functional MRI - a previously established neural measure of tactile self-other-differentiation. Afterwards, tactile detection thresholds during self- and other-touch were assessed, as well as dissociative states, interoceptive awareness, and social touch attitudes. Compared to placebo, ketamine administration elicited dissociation and reduced neural activity associated with self-other-differentiation in the right temporoparietal cortex, which was most pronounced during other-touch. This reduction correlated with ketamine-induced reductions in interoceptive awareness. The temporoparietal cortex showed higher connectivity to somatosensory cortex and insula during other- compared to self-touch. This difference was augmented by ketamine, and correlated with dissociation strength for somatosensory cortex. These results demonstrate that disrupting the self-experience through ketamine administration affects neural activity associated with self-other-differentiation in a region involved in touch perception and social cognition, especially with regard to social touch by someone else. This process may be driven by ketamine-induced effects on top-down signaling, rendering the processing of predictable self-generated and unpredictable other-generated touch more similar. These findings provide further evidence for the intricate relationship of the bodily self with the tactile sense.

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.

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.

Middleton, Perini et al. show that the role of Na(v)1.7 extends beyond pain perception. Using a multidisciplinary, cross-species approach, they show that Na(v)1.7 is also essential for C-low threshold mechanoreceptor function in mice and humans, regulating pleasant touch, punctate discrimination and sensitivity to cooling. Patients with bi-allelic loss of function mutations in the voltage-gated sodium channel Nav1.7 present with congenital insensitivity to pain (CIP), whilst low threshold mechanosensation is reportedly normal. Using psychophysics (n = 6 CIP participants and n = 86 healthy controls) and facial electromyography (n = 3 CIP participants and n = 8 healthy controls), we found that these patients also have abnormalities in the encoding of affective touch, which is mediated by the specialized afferents C-low threshold mechanoreceptors (C-LTMRs). In the mouse, we found that C-LTMRs express high levels of Nav1.7. Genetic loss or selective pharmacological inhibition of Nav1.7 in C-LTMRs resulted in a significant reduction in the total sodium current density, an increased mechanical threshold and reduced sensitivity to non-noxious cooling. The behavioural consequence of loss of Nav1.7 in C-LTMRs in mice was an elevation in the von Frey mechanical threshold and less sensitivity to cooling on a thermal gradient. Nav1.7 is therefore not only essential for normal pain perception but also for normal C-LTMR function, cool sensitivity and affective touch.

Touch is a powerful communication tool, but we have a limited understanding of the role played by particular physical features of interpersonal touch communication. In this study, adults living in Sweden performed a task in which messages (attention, love, happiness, calming, sadness, and gratitude) were conveyed by a sender touching the forearm of a receiver, who interpreted the messages. Two experiments (N = 32, N = 20) showed that within close relationships, receivers could identify the intuitive touch expressions of the senders, and we characterized the physical features of the touches associated with successful communication. Facial expressions measured with electromyography varied by message but were uncorrelated with communication performance. We developed standardized touch expressions and quantified the physical features with 3D hand tracking. In two further experiments (N = 20, N = 16), these standardized expressions were conveyed by trained senders and were readily understood by strangers unacquainted with the senders. Thus, the possibility emerges of a standardized, intuitively understood language of social touch.

Background: Slow stroking touch is generally perceived as pleasant and reduces thermal pain. However, the tactile stimuli applied tend to be short-lasting and typically applied to the forearm. This study aimed to compare the effects of a long-lasting brushing stimulus applied to the facial region and the forearm on pressure pain thresholds (PPTs) taken on the hand. Outcome measurements were touch satiety and concurrent mechanical pain thresholds of the hand. Methods: A total of 24 participants were recruited and randomized to receive continuous stroking, utilizing a robotic stimulator, at C-tactile (CT) favorable (3 cm/s) and non-favorable (30 cm/s) velocities applied to the right face or forearm. Ratings of touch pleasantness and unpleasantness and PPTs from the hypothenar muscle of the right hand were collected at the start of stroking and once per minute for 5 min. Results: A reduction in PPTs (increased pain sensitivity) was observed over time (P < 0.001). However, the increase in pain sensitivity was less prominent when the face was stroked compared to the forearm (P = 0.001). Continuous stroking resulted in a significant interaction between region and time (P = 0.008) on pleasantness ratings, with a decline in ratings observed over time for the forearm, but not on the face. Unpleasantness ratings were generally low. Conclusion: We observed touch satiety for 5 min of continuous robotic brushing on the forearm confirming previous studies. However, we did not observe any touch satiety for brushing the face. Mechanical pain sensitivity, measured in the hand, increased over the 5-min period but less so when paired with brushing on the face than with brushing on the forearm. The differential effects of brushing on the face and forearm on touch satiety and pain modulation may be by the differences in the emotional relevance and neuronal pathways involved.

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch.

Background

In clinical practice, EEGs are assessed visually. For practical reasons, recordings often need to be performed with a reduced number of electrodes and artifacts make assessment difficult. To circumvent these obstacles, different interpolation techniques can be utilized. These techniques usually perform better for higher electrode densities and values interpolated at areas far from electrodes can be unreliable. Using a method that learns the statistical distribution of the cortical electrical fields and predicts values may yield better results.

New Method

Generative networks based on convolutional layers were trained to upsample from 4 or 14 channels or to dynamically restore single missing channels to recreate 21-channel EEGs. 5,144 h of data from 1,385 subjects of the Temple University Hospital EEG database were used for training and evaluating the networks.

Comparison with Existing Method

The results were compared to spherical spline interpolation. Several statistical measures were used as well as a visual evaluation by board certified clinical neurophysiologists. Overall, the generative networks performed significantly better. There was no difference between real and network generated data in the number of examples assessed as artificial by experienced EEG interpreters whereas for data generated by interpolation, the number was significantly higher. In addition, network performance improved with increasing number of included subjects, with the greatest effect seen in the range 5–100 subjects.

Conclusions

Using neural networks to restore or upsample EEG signals is a viable alternative to spherical spline interpolation.