Novel Wearable Device for Mindful Sensorimotor Training: Integrating Motor Decoding and Somatosensory Stimulation for Neurorehabilitation.

Sensorimotor impairment is a prevalent condition requiring effective rehabilitation strategies. This study introduces a novel wearable device for Mindful Sensorimotor Training (MiSMT) designed for sensory and motor rehabilitation. Our MiSMT device combines motor training using myoelectric pattern recognition along sensory training using two tactile displays. This device offers a comprehensive solution, integrating electromyography and haptic feedback, lacking in existing devices. The device features eight electromyography channels, a rechargeable battery, and wireless Bluetooth or Wi-Fi connectivity for seamless communication with a computer or mobile device. Its flexible material allows for adaptability to various body parts, ensuring ease of use in diverse patients. The two tactile displays, with 16 electromagnetic actuators each, provide touch and vibration sensations up to 250 Hz. In this proof-of-concept study, we show improved two-point discrimination after 5 training sessions in participants with intact limbs (p=0.047). We also demonstrated successful acquisition, processing, and decoding of myoelectric signals in offline and online evaluations. In conclusion, the MiSMT device presents a promising tool for sensorimotor rehabilitation by combining motor execution and sensory training benefits. Further studies are required to assess its effectiveness in individuals with sensorimotor impairments. Integrating mindful sensory and motor training with innovative technology can enhance rehabilitation outcomes and improve the quality of life for those with sensorimotor impairments.

A narrative review of research linking non-sexual social touch to sleep quality.

This narrative review describes the current state of the literature that has examined associations between non-sexual social touch (i.e., affectionate touch, touch therapies, touch with animals and inanimate objects that mimic social touch) and sleep quality. It also highlights areas for future research to clarify the links and to identify underlying mechanisms. Most existing studies have focussed on and shown positive effects of touch therapies (e.g., massage, therapeutic touch) on sleep quality in clinical populations. Although there are fewer studies examining how other forms of social touch are linked with sleep quality, the existing research provides preliminary evidence supporting affectionate touch (e.g., hugging, skin-to-skin contact) and tactile contact with animals (e.g., dogs) and objects that mimic social touch (e.g., robots, weighted blankets) as predictors of better sleep quality, while touch deprivation and touch aversion are associated with worse sleep quality. Informed by the existing literature, we additionally reviewed potential relational-cognitive (e.g., felt-security) and neurobiological (e.g., oxytocin) mechanisms likely to underlie associations between social touch and sleep quality. Overall, current research supports associations between non-sexual social touch and sleep quality. However, future research is needed to establish these links for specific forms of social touch (and in various populations), to test explanatory mechanisms, and to identify boundary conditions. Understanding associations between non-sexual social touch and sleep quality can inform the development of touch-based interventions to improve sleep quality and health.

Impaired Discrimination of Electrocutaneous Stimulation in the Paretic Hand of Stroke Survivors.

Artificial sensory feedback via electrocutaneous stimulation can be used to assist or rehabilitate stroke survivors with sensory deficits. Conveying the magnitude of tactile stimuli is an important aspect of artificial sensory feedback. Here, we explore how stroke-related sensory deficits impact the ability of electrocutaneous stimulation to convey the magnitude of tactile stimuli. Using classical psychophysical methods, we quantified the threshold of detection and the just-noticeable difference of electrocutaneous stimulation current in five stroke survivors with unilateral sensory deficits. We show significantly greater (40%) stimulation currents are needed for initial perception on the paretic hand compared to the non-paretic hand. We also show significantly greater percent changes in stimulation current (140%) are needed for reliable incremental perception on the paretic hand compared to the non-paretic hand. Lastly, we show little correlation between electrocutaneous discrimination performance and clinical sensory assessments of light-touch and spatial mechanoperception. These findings can help guide the implementation of artificial sensory feedback as an assistive or rehabilitative intervention for individuals experiencing sensory loss after a stroke.Clinical Relevance- Our results can help guide the implementation of electrical stimulation as an assistive or rehabilitative intervention for individuals with sensory loss after stroke.

Blind people can actively manipulate virtual objects with a novel tactile device.

Frequently in rehabilitation, visually impaired persons are passive agents of exercises with fixed environmental constraints. In fact, a printed tactile map, i.e. a particular picture with a specific spatial arrangement, can usually not be edited. Interaction with map content, instead, facilitates the learning of spatial skills because it exploits mental imagery, manipulation and strategic planning simultaneously. However, it has rarely been applied to maps, mainly because of technological limitations. This study aims to understand if visually impaired people can autonomously build objects that are completely virtual. Specifically, we investigated if a group of twelve blind persons, with a wide age range, could exploit mental imagery to interact with virtual content and actively manipulate it by means of a haptic device. The device is mouse-shaped and designed to jointly perceive, with one finger only, local tactile height and inclination cues of arbitrary scalar fields. Spatial information can be mentally constructed by integrating local tactile cues, given by the device, with global proprioceptive cues, given by hand and arm motion. The experiment consisted of a bi-manual task, in which one hand explored some basic virtual objects and the other hand acted on a keyboard to change the position of one object in real-time. The goal was to merge basic objects into more complex objects, like a puzzle. The experiment spanned different resolutions of the tactile information. We measured task accuracy, efficiency, usability and execution time. The average accuracy in solving the puzzle was 90.5%. Importantly, accuracy was linearly predicted by efficiency, measured as the number of moves needed to solve the task. Subjective parameters linked to usability and spatial resolutions did not predict accuracy; gender modulated the execution time, with men being faster than women. Overall, we show that building purely virtual tactile objects is possible in absence of vision and that the process is measurable and achievable in partial autonomy. Introducing virtual tactile graphics in rehabilitation protocols could facilitate the stimulation of mental imagery, a basic element for the ability to orient in space. The behavioural variable introduced in the current study can be calculated after each trial and therefore could be used to automatically measure and tailor protocols to specific user needs. In perspective, our experimental setup can inspire remote rehabilitation scenarios for visually impaired people.

Caresses, whispers and affective faces: A theoretical framework for a multimodal interoceptive mechanism underlying ASMR and affective touch: An evolutionary and developmental perspective for understanding ASMR and affective touch as complementary processes within affiliative interactions.

Autonomous sensory meridian response (ASMR) and affective touch (AT) are two phenomena that have been independently investigated from separate lines of research. In this article, I provide a unified theoretical framework for understanding and studying them as complementary processes. I highlight their shared biological basis and positive effects on emotional and psychophysiological regulation. Drawing from evolutionary and developmental theories, I propose that ASMR results from the development of biological mechanisms associated with early affiliative behaviour and self-regulation, similar to AT. I also propose a multimodal interoceptive mechanism underlying both phenomena, suggesting that different sensory systems could specifically respond to affective stimulation (caresses, whispers and affective faces), where the integration of those inputs occurs in the brain's interoceptive hubs, allowing physiological regulation. The implications of this proposal are discussed with a view to future research that jointly examines ASMR and AT, and their potential impact on improving emotional well-being and mental health.

Deep Pressure Therapy: A Promising Anxiety Treatment for Individuals With High Touch Comfort?

One method for managing anxiety, a highly prevalent modern mental health condition, is the calming touch sensations of deep pressure therapy (DPT). Solutions for administering DPT include the Automatic Inflatable DPT (AID) Vest, which we designed in past work. Although benefits of DPT are clear in a subset of the related literature, these benefits are not ubiquitous. There is limited understanding of what factors lead to DPT success for a given user. In this work, we present the findings of a user study ( N = 25) that evaluates the effects of the AID Vest on anxiety. We compared physiological and self-reported measures of anxiety across Active (inflating) and Control (inactive) states of the AID Vest. In addition, we considered the presence of placebo effects and assessed participant comfort with social touch as a potential moderator. The results support our ability to reliably induce anxiety, and show that the Active AID Vest tended to reduce biosignals related to anxiety. We also found a significant relationship between comfort with social touch and reductions in self-reported state anxiety for the Active condition. Those who seek to successfully deploy DPT can benefit from this work.

Multiparametric non-linear TENS modulation to integrate intuitive sensory feedback.

Objective. Transcutaneous electrical nerve stimulation (TENS) has been recently introduced in neurorehabilitation and neuroprosthetics as a promising, non-invasive sensory feedback restoration alternative to implantable neurostimulation. Yet, the adopted stimulation paradigms are typically based on single-parameter modulations (e.g. pulse amplitude (PA), pulse-width (PW) or pulse frequency (PF)). They elicit artificial sensations characterized by a low intensity resolution (e.g. few perceived levels), low naturalness and intuitiveness, hindering the acceptance of this technology. To address these issues, we designed novel multiparametric stimulation paradigms, featuring the simultaneous modulation of multiple parameters, and implemented them in real-time tests of performance when exploited as artificial sensory inputs.Approach. We initially investigated the contribution of PW and PF variations to the perceived sensation magnitude through discrimination tests. Then, we designed three multiparametric stimulation paradigms comparing them with a standard PW linear modulation in terms of evoked sensation naturalness and intensity. The most performant paradigms were then implemented in real-time in a Virtual Reality-TENS platform to assess their ability to provide intuitive somatosensory feedback in a functional task.Main results. Our study highlighted a strong negative correlation between perceived naturalness and intensity: less intense sensations are usually deemed as more similar to natural touch. In addition, we observed that PF and PW changes have a different weight on the perceived sensation intensity. As a result, we adapted the activation charge rate (ACR) equation, proposed for implantable neurostimulation to predict the perceived intensity while co-modulating the PF and charge per pulse, to TENS (ACRT). ACRTallowed to design different multiparametric TENS paradigms with the same absolute perceived intensity. Although not reported as more natural, the multiparametric paradigm, based on sinusoidal PF modulation, resulted being more intuitive and subconsciously integrated than the standard linear one. This allowed subjects to achieve a faster and more accurate functional performance.Significance. Our findings suggest that TENS-based, multiparametric neurostimulation, despite not consciously perceived naturally, can provide integrated and more intuitive somatosensory information, as functionally proved. This could be exploited to design novel encoding strategies able to improve the performance of non-invasive sensory feedback technologies.

Effects of continuous tactile stimulation on auditory-evoked cortical responses depend on the audio-tactile phase.

Auditory perception can benefit from stimuli in non-auditory sensory modalities, as for example in lip-reading. Compared with such visual influences, tactile influences are still poorly understood. It has been shown that single tactile pulses can enhance the perception of auditory stimuli depending on their relative timing, but whether and how such brief auditory enhancements can be stretched in time with more sustained, phase-specific periodic tactile stimulation is still unclear. To address this question, we presented tactile stimulation that fluctuated coherently and continuously at 4 Hz with an auditory noise (either in-phase or anti-phase) and assessed its effect on the cortical processing and perception of an auditory signal embedded in that noise. Scalp-electroencephalography recordings revealed an enhancing effect of in-phase tactile stimulation on cortical responses phase-locked to the noise and a suppressive effect of anti-phase tactile stimulation on responses evoked by the auditory signal. Although these effects appeared to follow well-known principles of multisensory integration of discrete audio-tactile events, they were not accompanied by corresponding effects on behavioral measures of auditory signal perception. Our results indicate that continuous periodic tactile stimulation can enhance cortical processing of acoustically-induced fluctuations and mask cortical responses to an ongoing auditory signal. They further suggest that such sustained cortical effects can be insufficient for inducing sustained bottom-up auditory benefits.

Tactile Sensation Assisted Motor Imagery Training for Enhanced BCI Performance: A Randomized Controlled Study.

OBJECTIVE: Independent of conventional neurofeedback training, in this study, we propose a tactile sensation assisted motor imagery training (SA-MI Training) approach to improve the performance of MI-based BCI. METHODS: Twenty-six subjects were recruited and randomly divided into a Training-Group and a Control-Group. All subjects were required to perform three blocks of MI tasks. In the Training-Group, during the second block (SA-MI Training block), tactile stimulation was applied to the left or right wrist while the subjects were performing the left or right-hand MI task, while during the first block (Pre-Training block) and the third block (Post-Training block), subjects performed pure MI tasks without the tactile sensation assistance. In contrast, in the Control-Group, subjects performed the left and right-hand MI tasks in all three blocks. RESULTS: The performance of the Post-Training block (83.2 ± 11.4%) was significantly (p = 0.0014) higher than that of the Pre-Training block (73.2 ± 16.3%). By contrast, in the Control-Group, no significant difference was found among the three blocks. Moreover, after the SA-MI Training, the motor-related cortex activation (i.e., ERD/ERS) and the R 2 coefficient in the alpha-beta band were enhanced, while no training effect was found in the Control-Group. CONCLUSION: The proposed SA-MI Training approach can significantly improve the performance of MI, which provides a novel training framework for MI-based BCI. SIGNIFICANCE: It may be especially beneficial to those who are with difficulty in convention neurofeedback training or performing pure MI mental tasks to gain BCI control.

"No pain, no gain": The impact of autonomous sensory meridian response on pain perception.

Autonomous sensory meridian response (ASMR) is a phenomenon characterised by a static-like tingling sensation spreading from the scalp and neck to the periphery in response to a variety of audio, visual, and tactile triggers resulting in a highly relaxed state and boosted positive affect. The limited literature on this phenomenon points to a potential of ASMR to alleviate pain. Emerging evidence also suggests that ASMR may be linked to increased sensory sensitivity more broadly. This study aimed to objectively address these claims by administering an algometer (measure of pain tolerance), and a visual analog scale (VAS) (measure of subjective pain sensitivity) to ASMR experiencers and controls at baseline, following an ASMR video, and a control video. Findings indicate that ASMR experiencers have a higher pain sensitivity than controls; however, there was no difference between the two groups in terms of pain tolerance. In addition, any potential analgesic properties associated with experiencing ASMR may reflect protective properties of ASMR buffering against the increased pain sensitivity among ASMR experiencers relative to controls.

Identifying oscillations under multi-site sensory stimulation for high-level peripheral nerve injured patients: a pilot study.

Objective.For high-level peripheral nerve injuryed (PNI) patients with severe sensory dysfunction of upper extremities, identifying the multi-site tactile stimulation is of great importance to provide neurorehabilitation with sensory feedback. In this pilot study, we showed the feasibility of identifying multi-site and multi-intensity tactile stimulation in terms of electroencephalography (EEG).Approach.Three high-level PNI patients and eight non-PNI participants were recruited in this study. Four different sites over the upper arm, forearm, thumb finger and little finger were randomly stimulated at two intensities (both sensory-level) based on the transcutaneous electrical nerve stimulation. Meanwhile, 64-channel EEG signals were recorded during the passive tactile sense stimulation on each side.Main results.The spatial-spectral distribution of brain oscillations underlying multi-site sensory stimulation showed dominant power attenuation over the somatosensory and prefrontal cortices in both alpha-band (8-12 Hz) and beta-band (13-30 Hz). But there was no significant difference among different stimulation sites in terms of the averaged power spectral density over the region of interest. By further identifying different stimulation sites using temporal-spectral features, we found the classification accuracies were all above 89% for the affected arm of PNI patients, comparable to that from their intact side and that from the non-PNI group. When the stimulation site-intensity combinations were treated as eight separate classes, the classification accuracies were ranging from 88.89% to 99.30% for the affected side of PNI subjects, similar to that from their non-affected side and that from the non-PNI group. Other performance metrics, including specificity, precision, and F1-score, also showed a sound identification performance for both PNI patients and non-PNI subjects.Significance.These results suggest that reliable brain oscillations could be evoked and identified well, even though induced tactile sense could not be discerned by the PNI patients. This study have implication for facilitating bidirectional neurorehabilitation systems with sensory feedback.

Social Touch Somatotopically Affects Mental Body Representations.

In pre-Covid days, many daily actions such as hand shaking or cheek kissing implied physical contact between our body and that of other people. With respect to touching an inanimate object (objectual touch), touching a person (social touch) concerns not only touching a human body, but also that this body belongs to a living person. This fundamental difference also may affect the way we figure our own movements and perceptions or, in other words, how we mentally represent our own body. To test this hypothesis, we asked 30 neurotypical participants to perform mental rotation of images representing hands, full bodies, and feet (an active cognitive task able to activate body representations without need of moving) in two tactile conditions: holding (one in each hand) either the thumbs of another person (social touch) or two plastic cylinders (objectual touch) of about the same circumference and size. Results showed that only mental rotation of hand images was affected by varying the tactile conditions, in that participants were faster during social than objectual touch. This suggests that the nature of hand-related tactile input (social or objectual touch) influences local (hand) and not global (body) mental representations of the body, and in a very somatotopic manner (hands but not feet). We interpret these findings with reference to the differentiation between sensorimotor (body schema) and visuospatial (body image) dynamics in the mental representation of our body. The present study shows that external social factors can affect the internal mental representations of one's own body.

Identification of a Developmental Switch in Information Transfer between Whisker S1 and S2 Cortex in Mice.

The whiskers of rodents are a key sensory organ that provides critical tactile information for animal navigation and object exploration throughout life. Previous work has explored the developmental sensory-driven activation of the primary sensory cortex processing whisker information (wS1), also called barrel cortex. This body of work has shown that the barrel cortex is already activated by sensory stimuli during the first postnatal week. However, it is currently unknown when over the course of development these stimuli begin being processed by higher-order cortical areas, such as secondary whisker somatosensory area (wS2). Here we investigate the developmental engagement of wS2 by whisker stimuli and the emergence of corticocortical communication from wS1 to wS2. Using in vivo wide-field imaging and multielectrode recordings in control and conditional KO mice of either sex with thalamocortical innervation defects, we find that wS1 and wS2 are able to process bottom-up information coming from the thalamus from birth. We also identify that it is only at the end of the first postnatal week that wS1 begins to provide functional excitation into wS2, switching to more inhibitory actions after the second postnatal week. Therefore, we have uncovered a developmental window when information transfer between wS1 and wS2 reaches mature function.SIGNIFICANCE STATEMENT At the end of the first postnatal week, the primary whisker somatosensory area starts providing excitatory input to the secondary whisker somatosensory area 2. This excitatory drive weakens during the second postnatal week and switches to inhibition in the adult.

Evaluation of multiple perceptual qualities of transcutaneous electrical nerve stimulation for evoked tactile sensation in forearm amputees.

Objective. Evoked tactile sensation (ETS) elicited by transcutaneous electrical nerve stimulation (TENS) is promising to convey digit-specific sensory information to amputees naturally and non-invasively. Fitting ETS-based sensory feedback to amputees entails customizing coding of multiple sensory information for each stimulation site. This study was to elucidate the consistency of percepts and qualities by TENS at multiple stimulation sites in amputees retaining ETS.Approach. Five transradial amputees with ETS and fourteen able-bodied subjects participated in this study. Surface electrodes with small size (10 mm in diameter) were adopted to fit the restricted projected finger map on the forearm stump of amputees. Effects of stimulus frequency on sensory types were assessed, and the map of perceptual threshold for each sensation was characterized. Sensitivity for vibration and buzz sensations was measured using distinguishable difference in stimulus pulse width. Rapid assessments for modulation ranges of pulse width at fixed amplitude and frequency were developed for coding sensory information. Buzz sensation was demonstrated for location discrimination relating to prosthetic fingers.Main results. Vibration and buzz sensations were consistently evoked at 20 Hz and 50 Hz as dominant sensation types in all amputees and able-bodied subjects. Perceptual thresholds of different sensations followed a similar strength-duration curve relating stimulus amplitude to pulse width. The averaged distinguishable difference in pulse width was 12.84 ± 7.23µs for vibration and 15.21 ± 6.47µs for buzz in able-bodied subjects, and 14.91 ± 10.54µs for vibration and 11.30 ± 3.42µs for buzz in amputees. Buzz coding strategy enabled five amputees to discriminate contact of individual fingers with an overall accuracy of 77.85%.Significance. The consistency in perceptual qualities of dominant sensations can be exploited for coding multi-modality sensory feedback. A fast protocol of sensory coding is possible for fitting ETS-based, non-invasive sensory feedback to amputees.

[Touch Medicine - a complementary therapeutic approach exemplified by the treatment of depression]. / Berührungsmedizin ­ ein komplementärer therapeutischer Ansatz unter besonderer Berücksichtigung der Depressionsbehandlung.

Skin-to-skin-contact presents the earliest sensory experience of men and animals. Deprivation of age-relevant touch experiences during infancy results in compromised psychosocial and biological development. The 2021 Nobel Prize in Physiology or Medicine has been awarded for the discoveries of receptors for temperature and touch. Clinical studies have demonstrated the benefit of professional salutary touch for prevention and treatment of various illnesses. However, in the present practice of medicine the application of salutary touch does not meet adequate interest. Proposing a new medical discipline "Touch Medicine" we link the findings of modern touch research to clinical medicine. The treatment of depression which we conceive primarily as a disease afflicting the body will serve as an example to demonstrate the usefulness of touch therapy. Controlled studies and systematic reviews have convincingly shown antidepressive, anxiolytic and analgesic effects of salutary touch. The effectiveness and efficacy of touch therapy has also been demonstrated in many areas such as neonatology, pediatrics, oncology, and geriatrics. We discuss the underlying mechanisms on various explanatory levels including interoceptive and oxytocinergic mechanisms as well as the role of C tactile afferent nerve fibers.

Testing silicone digit extensions as a way to suppress natural sensation to evaluate supplementary tactile feedback.

Dexterous use of the hands depends critically on sensory feedback, so it is generally agreed that functional supplementary feedback would greatly improve the use of hand prostheses. Much research still focuses on improving non-invasive feedback that could potentially become available to all prosthesis users. However, few studies on supplementary tactile feedback for hand prostheses demonstrated a functional benefit. We suggest that confounding factors impede accurate assessment of feedback, e.g., testing non-amputee participants that inevitably focus intently on learning EMG control, the EMG's susceptibility to noise and delays, and the limited dexterity of hand prostheses. In an attempt to assess the effect of feedback free from these constraints, we used silicone digit extensions to suppress natural tactile feedback from the fingertips and thus used the tactile feedback-deprived human hand as an approximation of an ideal feed-forward tool. Our non-amputee participants wore the extensions and performed a simple pick-and-lift task with known weight, followed by a more difficult pick-and-lift task with changing weight. They then repeated these tasks with one of three kinds of audio feedback. The tests were repeated over three days. We also conducted a similar experiment on a person with severe sensory neuropathy to test the feedback without the extensions. Furthermore, we used a questionnaire based on the NASA Task Load Index to gauge the subjective experience. Unexpectedly, we did not find any meaningful differences between the feedback groups, neither in the objective nor the subjective measurements. It is possible that the digit extensions did not fully suppress sensation, but since the participant with impaired sensation also did not improve with the supplementary feedback, we conclude that the feedback failed to provide relevant grasping information in our experiments. The study highlights the complex interaction between task, feedback variable, feedback delivery, and control, which seemingly rendered even rich, high-bandwidth acoustic feedback redundant, despite substantial sensory impairment.

A compact system for simultaneous stimulation and recording for closed-loop myoelectric control.

BACKGROUND: Despite important advancements in control and mechatronics of myoelectric prostheses, the communication between the user and his/her bionic limb is still unidirectional, as these systems do not provide somatosensory feedback. Electrotactile stimulation is an attractive technology to close the control loop since it allows flexible modulation of multiple parameters and compact interface design via multi-pad electrodes. However, the stimulation interferes with the recording of myoelectric signals and this can be detrimental to control. METHODS: We present a novel compact solution for simultaneous recording and stimulation through dynamic blanking of stimulation artefacts. To test the system, a feedback coding scheme communicating wrist rotation and hand aperture was developed specifically to stress the myoelectric control while still providing meaningful information to the subjects. Ten subjects participated in an experiment, where the quality of closed-loop myoelectric control was assessed by controlling a cursor in a two degrees of freedom target-reaching task. The benchmark performance with visual feedback was compared to that achieved by combining visual feedback and electrotactile stimulation as well as by using electrotactile feedback only. RESULTS: There was no significant difference in performance between visual and combined feedback condition with regards to successfully reached targets, time to reach a target, path efficiency and the number of overshoots. Therefore, the quality of myoelectric control was preserved in spite of the stimulation. As expected, the tactile condition was significantly poorer in completion rate (100/4% and 78/25% for combined and tactile condition, respectively) and time to reach a target (9/2 s and 13/4 s for combined and tactile condition, respectively). However, the performance in the tactile condition was still good, with no significant difference in path efficiency (38/8%) and the number of overshoots (0.5/0.4 overshoots), indicating that the stimulation was meaningful for the subjects and useful for closed-loop control. CONCLUSIONS: Overall, the results demonstrated that the developed system can provide robust closed-loop control using electrotactile stimulation. The system supports different encoding schemes and allows placing the recording and stimulation electrodes next to each other. This is an important step towards an integrated solution where the developed unit will be embedded into a prosthetic socket.

Feedforward and feedback pathways of nociceptive and tactile processing in human somatosensory system: A study of dynamic causal modeling of fMRI data.

Nociceptive and tactile information is processed in the somatosensory system via reciprocal (i.e., feedforward and feedback) projections between the thalamus, the primary (S1) and secondary (S2) somatosensory cortices. The exact hierarchy of nociceptive and tactile information processing within this 'thalamus-S1-S2' network and whether the processing hierarchy differs between the two somatosensory submodalities remains unclear. In particular, two questions related to the ascending and descending pathways have not been addressed. For the ascending pathways, whether tactile or nociceptive information is processed in parallel (i.e., 'thalamus-S1' and 'thalamus-S2') or in serial (i.e., 'thalamus-S1-S2') remains controversial. For the descending pathways, how corticothalamic feedback regulates nociceptive and tactile processing also remains elusive. Here, we aimed to investigate the hierarchical organization for the processing of nociceptive and tactile information in the 'thalamus-S1-S2' network using dynamic causal modeling (DCM) combined with high-temporal-resolution fMRI. We found that, for both nociceptive and tactile information processing, both S1 and S2 received inputs from thalamus, indicating a parallel structure of ascending pathways for nociceptive and tactile information processing. Furthermore, we observed distinct corticothalamic feedback regulations from S1 and S2, showing that S1 generally exerts inhibitory feedback regulation independent of external stimulation whereas S2 provides additional inhibition to the thalamic activity during nociceptive and tactile information processing in humans. These findings revealed that nociceptive and tactile information processing have similar hierarchical organization within the somatosensory system in the human brain.

Cognitive processes and a centre-of-pressure error-based moving light-touch biofeedback.

Lightly touching an earth-fixed external surface with the forefinger provides somatosensory information that reduces the center of pressure (CoP) oscillations. If this surface were to move slowly, the central nervous system (CNS) would misinterpret its movement as body self-motion, and involuntary compensatory sway responses would appear, resulting in a significant coupling between finger and CoP motions. We designed a forefinger moving light-touch biofeedback based on this finding, which controls the surface velocity to drive the CoP towards a target position. Here, we investigate this biofeedback resistance to cognitive processes. In addition to a baseline, the experimental protocol includes four main conditions. In the first, participants were utterly naive about the feedback. Then, they received additional reliable sensory information. The third condition ensured their full awareness of the external nature of the surface motion. Finally, the experimenter notified them that the external motion drives their balance and asked them to reject its influence. Our investigation shows that despite the robustness of the proposed biofeedback, light-touch remains penetrable by cognitive processes. For participants to dramatically reduce the existing coupling between the finger and CoP motions, they should be aware of the external motion, how it impacts sway, and actively reject its influence. The main implication of our findings is that light-touch exhibits the same cognitive flexibility as vision when artificially stimulated. This could be interpreted as a defense mechanism to re-weight these two sensory inputs in a moving environment.

Neural network for Braille reading and the speech-reading convergence in the blind: Similarities and differences to visual reading.

All writing systems represent units of spoken language. Studies on the neural correlates of reading in different languages show that this skill relies on access to brain areas dedicated to speech processing. Speech-reading convergence onto a common perisylvian network is therefore considered universal among different writing systems. Using fMRI, we test whether this holds true also for tactile Braille reading in the blind. The neural networks for Braille and visual reading overlapped in the left ventral occipitotemporal (vOT) cortex. Even though we showed similar perisylvian specialization for speech in both groups, blind subjects did not engage this speech system for reading. In contrast to the sighted, speech-reading convergence in the blind was absent in the perisylvian network. Instead, the blind engaged vOT not only in reading but also in speech processing. The involvement of the vOT in speech processing and its engagement in reading in the blind suggests that vOT is included in a modality independent language network in the blind, also evidenced by functional connectivity results. The analysis of individual speech-reading convergence suggests that there may be segregated neuronal populations in the vOT for speech processing and reading in the blind.