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"Touch - physiology"
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Touch : the science of hand, heart, and mind
\"The New York Times bestselling author examines how our sense of touch and emotion are interconnected Johns Hopkins neuroscientist and bestselling author of The Compass of Pleasure, David J. Linden presents an engaging and fascinating examination of how the interface between our sense of touch and our emotional responses affects our social interactions as well as our general health and development. Accessible in its wit and clarity, Touch explores scientific advances in the understanding of touch that help explain our sense of self and our experience of the world. From skin to nerves to brain, the organization of the body's touch circuits powerfully influences our lives-affecting everything from consumer choice to sexual intercourse, tool use to the origins of language, chronic pain to healing. Interpersonal touch is crucial to social bonding and individual development. Linden lucidly explains how sensory and emotional context work together to distinguish between perceptions of what feels good and what feels bad. Linking biology and behavioral science, Linden offers an entertaining and enlightening answer to how we feel in every sense of the word\"-- Provided by publisher.
Book
Attention and control of posture: the effects of light touch on the center-of-pressure time series regularity and simple reaction time task
The stabilizing influence of a light touch (LT) on a postural sway has been consistently shown in the literature, however there is still no consensus in what way attentional resources are used when adopting LT during standing. To better elucidate the underlying mechanisms we introduced additional feedback (LT), which seems to distracts from postural control, and verified it by center of pressure (COP) regularity level and simple reaction time task. 25 healthy students randomly performed eight postural tasks, four without (NoRT)/ four with simple reaction task (RT). COP displacements were measured on a force plate in two visual conditions: eyes open/closed and two sensory conditions: without (NoLT)/with light touch (LT). Participants were asked to consider the postural task as the primary task. Although simple reaction time did not differ between postural conditions (
p
> 0.05), LT decreased postural sway velocity in anteroposterior direction (
p
< 0.001, η2 = 0.86) and decreased standard deviation (
p
< 0.001, η2 = 0.91) in both, reaction and visual conditions. Interestingly, RT task modified subjects behavior in NoLT conditions and caused slower COP velocity (
p
< 0.001, η2 = 0.53) without changes in signal regularity. Results also showed a significant increase in irregularity during standing with LT (
p
< 0.001, η2 = 0.86) in both vision and reaction conditions, suggesting that the signal was more random. Current results suggests that providing LT enhance postural steadiness and also seem to redirect attention externally, as shown by increased signal irregularity. Hence, LT possibly reduce the attention invested in the postural task itself. A RT task can be not sensitive enough to detect such subtle changes.
Journal Article
Oxytocin administration enhances pleasantness and neural responses to gentle stroking but not moderate pressure social touch by increasing peripheral concentrations
Social touch constitutes a key component of human social relationships, although in some conditions with social dysfunction, such as autism, it can be perceived as unpleasant. We have previously shown that intranasal administration of oxytocin facilitates the pleasantness of social touch and activation of brain reward and social processing regions, although it is unclear if it influences responses to gentle stroking touch mediated by cutaneous C-touch fibers or pressure touch mediated by other types of fibers. Additionally, it is unclear whether endogenous oxytocin acts via direct entry into the brain or by increased peripheral blood concentrations.
In a randomized controlled design, we compared effects of intranasal (direct entry into the brain and increased peripheral concentrations) and oral (only peripheral increases) oxytocin on behavioral and neural responses to social touch targeting C-touch (gentle-stroking) or other (medium pressure without stroking) cutaneous receptors.
Although both types of touch were perceived as pleasant, intranasal and oral oxytocin equivalently enhanced pleasantness ratings and responses of reward, orbitofrontal cortex, and social processing, superior temporal sulcus, regions only to gentle-stroking not medium pressure touch. Furthermore, increased blood oxytocin concentrations predicted the pleasantness of gentle stroking touch. The specificity of neural effects of oxytocin on C-touch targeted gentle stroking touch were confirmed by time-course extraction and classification analysis.
Increased peripheral concentrations of oxytocin primarily modulate its behavioral and neural responses to gentle social touch mediated by C-touch fibers. Findings have potential implications for using oxytocin therapeutically in conditions where social touch is unpleasant.
Key Technological Projects of Guangdong Province grant 2018B030335001.
NCT05265806.
Journal Article
Acute tryptophan depletion alters affective touch perception
RationaleAffiliative tactile interactions help regulate physiological arousal and confer resilience to acute and chronic stress. C-tactile afferents (CTs) are a population of unmyelinated, low threshold mechanosensitive cutaneous nerve fibres which respond optimally to a low force stimulus, moving at between 1 and 10 cm/s. As CT firing frequencies correlate positively with subjective ratings of touch pleasantness, they are hypothesised to form the first stage of encoding affiliative tactile interactions. Serotonin is a key modulator of social responses with known effects on bonding.ObjectivesThe aim of the present study was to determine the effect of acutely lowering central serotonin levels on perceptions of CT-targeted affective touch.MethodsIn a double blind, placebo-controlled design, the effect of acute tryptophan depletion (ATD) on 25 female participants’ ratings of directly and vicariously experienced touch was investigated. Psychophysical techniques were used to deliver dynamic tactile stimuli; some velocities were targeted to optimally activate CTs (1–10 cm/s), whereas other, faster and slower strokes fell outside the CT optimal range. Discriminative tactile function, cold pain threshold and tolerance were also measured.ResultsATD significantly increased pleasantness ratings of both directly and vicariously experienced affective touch, increasing discrimination of the specific hedonic value of CT targeted velocities. While ATD had no effect on either tactile or cold pain thresholds, there was a trend for reduced tolerance to cold pain.ConclusionsThese findings are consistent with previous reports that depletion of central serotonin levels modulates neural and behavioural responsiveness to appetitive sensory signals.
Journal Article
Cross‐Modal Transfer Effects of the Go/No‐Go Training With Visual Stimuli
Introduction Motor task performance guided by one sensory modality (e.g., visual stimuli) can be improved by training; however, whether this training can also improve performance on the same task guided by another sensory modality remains uncertain (e.g., tactile stimuli). This study examined the effects of Go/No‐go task training using visual stimulus cues on Go/No‐go task performance using tactile cues and whether training also influences the dominance of the sensory modality. Methods Go/No‐go tasks and a temporal order judgment (TOJ) task were performed by 24 right‐handed, healthy adults on days 1 and 5 of the 5‐day experiment. Furthermore, a subpopulation (the training group) practiced the Go/No‐go task with visual stimulus cues on days 2–4, whereas the remaining control group did not practice the task. Results The training group demonstrated significantly reduced reaction times (RTs) on both the visual and tactile Go/No‐go tasks by day 5, whereas the control group demonstrated significantly reduced RTs only on the tactile Go/No‐go task. The RT change was also significantly greater in the training group than in the control group for both modalities. Conversely, no significant change in the TOJ for visual and tactile stimuli was observed between the groups. Conclusion These results indicate that motor training with visual guidance can improve performance on the same task guided by tactile stimuli, possibly due to neuroplastic changes in the multimodal association cortices. Visual modality training reduced reaction time. The rate of change was greater in the visual modality training group.
Journal Article
Touched by loneliness—how loneliness impacts the response to observed human touch: a tDCS study
Abstract
Lonely people often crave connectedness. However, they may also experience their environment as threatening, entering a self-preserving state that perpetuates loneliness. Research shows conflicting evidence about their response to positive social cues, and little is known about their experience of observed human touch. The right inferior frontal gyrus (rIFG) is part of an observation–execution network implicated in observed touch perception. Correlative studies also point to rIFG’s involvement in loneliness. We examined the causal effect of rIFG anodal transcranial direct current stimulation on high- and low-loneliness individuals observing human touch. In a cross-over design study, 40 participants watched pictures of humans or objects touching or not touching during anodal and sham stimulations. Participants indicated whether pictures contained humans or objects, and their reaction time was measured. Results show that the reaction time of low-loneliness individuals to observed human touch was significantly slower during anodal stimulation compared to high-loneliness individuals, possibly due to them being more emotionally distracted by it. Lonely individuals also reported less liking of touch. Our findings support the notion that lonely individuals are not drawn to positive social cues. This may help explain the perpetuation of loneliness, despite social opportunities that could be available to lonely people.
Journal Article
Tactile versus motor imagery: differences in corticospinal excitability assessed with single-pulse TMS
Tactile Imagery (TI) remains a fairly understudied phenomenon despite growing attention to this topic in recent years. Here, we investigated the effects of TI on corticospinal excitability by measuring motor evoked potentials (MEPs) induced by single-pulse transcranial magnetic stimulation (TMS). The effects of TI were compared with those of tactile stimulation (TS) and kinesthetic motor imagery (kMI). Twenty-two participants performed three tasks in randomly assigned order: imagine finger tapping (kMI); experience vibratory sensations in the middle finger (TS); and mentally reproduce the sensation of vibration (TI). MEPs increased during both kMI and TI, with a stronger increase for kMI. No statistically significant change in MEP was observed during TS. The demonstrated differential effects of kMI, TI and TS on corticospinal excitability have practical implications for devising the imagery-based and TS-based brain–computer interfaces (BCIs), particularly the ones intended to improve neurorehabilitation by evoking plasticity changes in sensorimotor circuitry.
Journal Article
Multimodal tactile sensing fused with vision for dexterous robotic housekeeping
As robots are increasingly participating in our daily lives, the quests to mimic human abilities have driven the advancements of robotic multimodal senses. However, current perceptual technologies still unsatisfied robotic needs for home tasks/environments, particularly facing great challenges in multisensory integration and fusion, rapid response capability, and highly sensitive perception. Here, we report a flexible tactile sensor utilizing thin-film thermistors to implement multimodal perceptions of pressure, temperature, matter thermal property, texture, and slippage. Notably, the tactile sensor is endowed with an ultrasensitive (0.05 mm/s) and ultrafast (4 ms) slip sensing that is indispensable for dexterous and reliable grasping control to avoid crushing fragile objects or dropping slippery objects. We further propose and develop a robotic tactile-visual fusion architecture that seamlessly encompasses multimodal sensations from the bottom level to robotic decision-making at the top level. A series of intelligent grasping strategies with rapid slip feedback control and a tactile-visual fusion recognition strategy ensure dexterous robotic grasping and accurate recognition of daily objects, handling various challenging tasks, for instance grabbing a paper cup containing liquid. Furthermore, we showcase a robotic desktop-cleaning task, the robot autonomously accomplishes multi-item sorting and cleaning desktop, demonstrating its promising potential for smart housekeeping.
The authors report a multimodal tactile sensor with perceptions of pressure, temperature, material thermal property, texture, slippage, and a robotic decision-making tactile-visual fusion architecture which allows robots for dexterous housekeeping.
Journal Article
Anodal transcranial direct current stimulation over the posterior parietal cortex reduces the onset time to the rubber hand illusion and increases the body ownership
The body ownership induced by the rubber hand illusion (RHI) has been related to a neural network involving a frontal–parietal circuit. Previous functional neuroimaging studies have demonstrated neural activation in the parietal area relative to the multisensory integration processing and to the recalibration of the felt position of body while a ventral premotor cortex activation has been linked to bodily self-attribution during the RHI. Our study aimed to investigate the effects of transcranial direct current stimulation (tDCS) on the posterior parietal cortex (PPC) or on the premotor cortex (PMv) during RHI to address the specific roles of these two brain areas in the illusion. 156 young adult participants (21.2 ± 3.13 years old; all right-handed) were enrolled for this between-subjects design experiment. Participants received anodal, cathodal and sham tDCS in three different sessions on the right PPC or right PMv and experienced visual–tactile stimulation from the brushes touching the rubber hand and their own left hand in synchronous or asynchronous manner. The RHI was quantified by the (1) onset time for the feeling of body ownership of the rubber hand, (2) proprioceptive drift, and (3) questionnaire about the intensity of the illusion as reported by the participant. All subjects felt the RHI during the synchronous condition. However, we found that the illusion onset time can be modulated by the anodal tDCS condition on the PPC: anodal tDCS decreased the illusion onset time and the subjective experience of body ownership. These findings suggest that the parietal area plays a crucial role in the speed of visual and tactile multisensory integration in the RHI and introduce tDCS as technique that can accelerate the time to integrate an artificial body part and increased the perception of body ownership.
Journal Article
Neuromorphic hardware for somatosensory neuroprostheses
In individuals with sensory-motor impairments, missing limb functions can be restored using neuroprosthetic devices that directly interface with the nervous system. However, restoring the natural tactile experience through electrical neural stimulation requires complex encoding strategies. Indeed, they are presently limited in effectively conveying or restoring tactile sensations by bandwidth constraints. Neuromorphic technology, which mimics the natural behavior of neurons and synapses, holds promise for replicating the encoding of natural touch, potentially informing neurostimulation design. In this perspective, we propose that incorporating neuromorphic technologies into neuroprostheses could be an effective approach for developing more natural human-machine interfaces, potentially leading to advancements in device performance, acceptability, and embeddability. We also highlight ongoing challenges and the required actions to facilitate the future integration of these advanced technologies.
Neuroprosthetic devices have recently emerged as promising solutions to restore sensory-motor functions lost due to injury or neurological diseases. In this perspective, Donati and Valle propose to combine neuroprostheses with neuromorphic technologies for designing more natural human-machine interfaces with possible improvements in device performance, acceptability, and embeddability.
Journal Article