Expression responses of XTH genes in tomato and potato to environmental mechanical forces: focus on behavior in response to rainfall, wind and touch

Rainfall, wind and touch, as mechanical forces, were mimicked on 6-week-old soil-grown tomato and potato under controlled conditions. Expression level changes of xyloglucan endotransglucosylase/hydrolase genes (XTHs) of tomato (Solanum lycopersicum L. cv. Micro Tom; SlXTHs) and potato (Solanum tuberosum L. cv. Desirée; StXTHs) were analyzed in response to these mechanical forces. Transcription intensity of every SlXTHs of tomato was altered in response to rainfall, while the expression intensity of 72% and 64% of SlXTHs was modified by wind and touch, respectively. Ninety-one percent of StXTHs (32 out of 35) in potato responded to the rainfall, while 49% and 66% of the StXTHs were responsive to the wind and touch treatments, respectively. As previously demonstrated, all StXTHs were responsive to ultrasound treatment, and all were sensitive to one or more of the environmental mechanical factors examined in the current study. To our best knowledge, this is the first study to demonstrate that these ubiquitous mechanical environmental cues, such as rainfall, wind and touch, influence the transcription of most XTHs examined in both species.

Role of tactile stimulation during the preweaning period on the development of the peripheral sensory sural (SU) nerve in adult artificially reared female rat

Maternal deprivation, as a result of the artificial rearing (AR) paradigm, disturbs electrophysiological and histological characteristics of the peripheral sensory sural (SU) nerve of infant and adult male rats. Such changes are prevented by providing tactile or social stimulation during isolation. AR also affects the female rat's brain and behavior; however, it is unknown whether this early adverse experience also alters their SU nerve development or if tactile stimulation might prevent these possible developmental effects. To assess these possibilities, the electrophysiological and histological characteristics of the SU nerve from adult diestrus AR female rats that: (i) received no tactile stimulation (AR group), (ii) received tactile stimulation in the anogenital and body area (AR-Tactile group), or (iii) were mother reared (MR group) were determined. We found that the amplitude, but not the area, of the evoked compound action potential response in SU nerves of AR rats was lower than those of SU nerves of MR female rats. Tactile stimulation prevented these effects. Additionally, we found a reduction in the outer diameter and myelin thickness of axons, as well as a large proportion of axons with low myelin thickness in nerves of AR rats compared to the nerves of the MR and AR-Tactile groups of rats; however, tactile stimulation only partially prevented these effects. Our data indicate that maternal deprivation disturbs the development of sensory SU nerves in female rats, whereas tactile stimulation partially prevents the changes generated by AR. Considering that our previous studies have shown more severe effects of AR on male SU nerve development, we suggest that sex-associated factors may be involved in these processes.

Maternal prenatal depressive symptoms and child brain responses to affective touch at two years of age

BACKGROUND

Touch is an essential form of mother-child interaction, instigating better social bonding and emotional stability.

METHODS

We used diffuse optical tomography to explore the relationship between total haemoglobin (HbT) responses to affective touch in the child's brain at two years of age and maternal self-reported prenatal depressive symptoms (EPDS). Affective touch was implemented via slow brushing of the child's right forearm at 3 cm/s and non-affective touch via fast brushing at 30 cm/s and HbT responses were recorded on the left hemisphere.

RESULTS

We discovered a cluster in the postcentral gyrus exhibiting a negative correlation (Pearson's r = -0.84, p = 0.015 corrected for multiple comparisons) between child HbT response to affective touch and EPDS at gestational week 34. Based on region of interest (ROI) analysis, we found negative correlations between child responses to affective touch and maternal prenatal EPDS at gestational week 14 in the precentral gyrus, Rolandic operculum and secondary somatosensory cortex. The responses to non-affective touch did not correlate with EPDS in these regions.

LIMITATIONS

The number of mother-child dyads was 16. However, by utilising high-density optode arrangements, individualised anatomical models, and video and accelerometry to monitor movement, we were able to minimize methodological sources of variability in the data.

CONCLUSIONS

The results show that maternal depressive symptoms during pregnancy may be associated with reduced child responses to affective touch in the temporoparietal cortex. Responses to affective touch may be considered as potential biomarkers for psychosocial development in children. Early identification of and intervention in maternal depression may be important already during early pregnancy.

Slow touch and ultrafast pain fibres: Revisiting peripheral nerve classification

One hundred years ago, Erlanger and Gasser demonstrated that conduction velocity is correlated with the diameter of a peripheral nerve axon. Later, they also demonstrated that the functional role of the axon is related to its diameter: touch is signalled by large-diameter axons, whereas pain and temperature are signalled by small-diameter axons. Certain discoveries in recent decades prompt a modification of this canonical classification. Here, we review the evidence for unmyelinated (C) fibres signalling touch at a slow conduction velocity and likely contributing to affective aspects of tactile information. We also review the evidence for large-diameter Aβ afferents signalling pain at ultrafast conduction velocity and likely contributing to the rapid nociceptive withdrawal reflex. These discoveries imply that conduction velocity is not as clear-cut an indication of the functional role of the axon as previously thought. We finally suggest that a future taxonomy of the peripheral afferent nervous system might be based on the combination of the axońs molecular expression and electrophysiological response properties.

Tactile emoticons: Conveying social emotions and intentions with manual and robotic tactile feedback during social media communications

Touch offers important non-verbal possibilities for socioaffective communication. Yet most digital communications lack capabilities regarding exchanging affective tactile messages (tactile emoticons). Additionally, previous studies on tactile emoticons have not capitalised on knowledge about the affective effects of certain mechanoreceptors in the human skin, e.g., the C-Tactile (CT) system. Here, we examined whether gentle manual stroking delivered in velocities known to optimally activate the CT system (defined as 'tactile emoticons'), during lab-simulated social media communications could convey increased feelings of social support and other prosocial intentions compared to (1) either stroking touch at CT sub-optimal velocities, or (2) standard visual emoticons. Participants (N = 36) felt more social intent with CT-optimal compared to sub-optimal velocities, or visual emoticons. In a second, preregistered study (N = 52), we investigated whether combining visual emoticons with tactile emoticons, this time delivered at CT-optimal velocities by a soft robotic device, could enhance the perception of prosocial intentions and affect participants' physiological measures (e.g., skin conductance rate) in comparison to visual emoticons alone. Visuotactile emoticons conveyed more social intent overall and in anxious participants affected physiological measures more than visual emoticons. The results suggest that emotional social media communications can be meaningfully enhanced by tactile emoticons.

Conductive block copolymer elastomers and psychophysical thresholding for accurate haptic effects

Electrotactile stimulus is a form of sensory substitution in which an electrical signal is perceived as a mechanical sensation. The electrotactile effect could, in principle, recapitulate a range of tactile experience by selective activation of nerve endings. However, the method has been plagued by inconsistency, galvanic reactions, pain and desensitization, and unwanted stimulation of nontactile nerves. Here, we describe how a soft conductive block copolymer, a stretchable layout, and concentric electrodes, along with psychophysical thresholding, can circumvent these shortcomings. These purpose-designed materials, device layouts, and calibration techniques make it possible to generate accurate and reproducible sensations across a cohort of 10 human participants and to do so at ultralow currents (≥6 microamperes) without pain or desensitization. This material, form factor, and psychophysical approach could be useful for haptic devices and as a tool for activation of the peripheral nervous system.

Tactile breathing guidance increases oxygen saturation but not alertness or hypoxia symptoms

We investigated the effect of tactile guided slow deep breathing compared with that of spontaneous breathing on blood oxygen saturation (SpO2), alertness, and hypoxia symptoms during acute hypobaric hypoxia. We also evaluated the usability of this tactile breathing guidance. Twelve male military pilots were exposed to a simulated altitude of 4,572 m (15,000 ft) in a repeated measures study while breathing spontaneously and during tactile guided slow deep breathing. Under both breathing conditions, measurements were performed at rest and during the performance of a cognitive task. The Stanford Sleepiness Scale was used to rate alertness, and hypoxia symptoms were reported using a list of general hypoxia symptoms. Usability was evaluated in a questionnaire. Tactile guidance of slow deep breathing significantly increased (p <.001) the SpO2 - 88% (95% confidence interval (CI) [84%, 91%]) at rest and 85% (95% CI [81%, 88%]) during the cognitive task - compared with spontaneous breathing - 78% (95% CI [75%, 81%]) at rest and 78% (95% CI [76%, 80%]) during the cognitive task. This increase in SpO2 had no effect on the level of alertness and number of hypoxia symptoms. Pilots were positive about the intensity and sensation of the vibration signal, but had difficulty following the vibration pattern during the cognitive task. Pre-training may improve slow deep breathing technique during performance of cognitive tasks.

A scoping review on examination approaches for identifying tactile deficits at the upper extremity in individuals with stroke

PURPOSE

Accurate perception of tactile stimuli is essential for performing and learning activities of daily living. Through this scoping review, we sought to summarize existing examination approaches for identifying tactile deficits at the upper extremity in individuals with stroke. The goal was to identify current limitations and future research needs for designing more comprehensive examination tools.

METHODS

A scoping review was conducted in accordance with the Joanna Briggs Institute methodological framework and the PRISMA for Scoping Reviews (PRISMA-ScR) guidelines. A database search for tactile examination approaches at the upper extremity of individuals with stroke was conducted using Medline (Ovid), The Cochrane Library (Wiley), CINAHL Plus with Full Text (Ebsco), Scopus (Elsevier), PsycInfo (Ebsco), and Proquest Dissertations and Theses Global. Original research and review articles that involved adults (18 years or older) with stroke, and performed tactile examinations at the upper extremity were eligible for inclusion. Data items extracted from the selected articles included: if the examination was behavioral in nature and involved neuroimaging, the extent to which the arm participated during the examination, the number of possible outcomes of the examination, the type(s) of tactile stimulation equipment used, the location(s) along the arm examined, the peripheral nerves targeted for examination, and if any comparison was made with the non-paretic arm or with the arms of individuals who are neurotypical.

RESULTS

Twenty-two articles met the inclusion criteria and were accepted in this review. Most examination approaches were behavioral in nature and involved self-reporting of whether a tactile stimulus was felt while the arm remained passive (i.e., no volitional muscle activity). Typically, the number of possible outcomes with these behavioral approaches were limited (2-3), whereas the neuroimaging approaches had many more possible outcomes ( > 15 ). Tactile examinations were conducted mostly at the distal locations along the arm (finger or hand) without targeting any specific peripheral nerve. Although a majority of articles compared paretic and non-paretic arms, most did not compare outcomes to a control group of individuals who are neurotypical.

DISCUSSION

Our findings noted that most upper extremity tactile examinations are behavioral approaches, which are subjective in nature, lack adequate resolution, and are insufficient to identify the underlying neural mechanisms of tactile deficits. Also, most examinations are administered at distal locations of the upper extremity when the examinee's arm is relaxed (passive). Further research is needed to develop better tactile examination tools that combine behavioral responses and neurophysiological outcomes, and allow volitional tactile exploration. Approaches that include testing of multiple body locations/nerves along the upper extremity, provide higher resolution of outcomes, and consider normative comparisons with individuals who are neurotypical may provide a more comprehensive understanding of the tactile deficits occurring following a stroke.

Touch me or touch me not: Emotion regulation by affective touch in human adults

In mammals, including humans, affective touch (AT) supports the establishment and maintenance of social connections and mitigates the effects of social conflict and ostracism. AT is used to describe slowly moving, low-forced mechanical stimulation that is frequently perceived as pleasant. In humans, AT has been addressed particularly for its role in promoting bonding and emotional regulation during early development; however, more recent studies have suggested that AT also preserves physical and emotional well-being in adulthood. Here, we investigated whether AT can buffer adults' experience of negative emotions as reflected in their behavioral and physiological responses to emotionally arousing stimuli. Participants were stimulated on their forearms using AT or tapping (T) while they viewed a series of emotionally arousing and neutral images, and we measured their skin conductance response and their explicit rating of the images' unpleasantness. We found that AT, but not T, reduced the arousal and perceived unpleasantness of the emotional stimuli but not the neutral ones, revealing the soothing role of AT in emotional contexts. The second aim of the study was to explore the possibility that AT might benefit some individuals more than others, according to their individual differences. To this aim, we assessed individuals' empathy and sensory processing sensitivity, as well as their perception of AT itself. Results revealed that while empathy did not predict changes in emotional processing irrespective of tactile stimulation, individuals with higher sensitivity reported AT as less pleasant. We discuss the possible factors mediating the observed interindividual variability in AT perception. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Biomechanical Considerations of Refreshable Braille and Tactile Graphics Toward Equitable Access: A Review

This review highlights the biomechanical foundations of braille and tactile graphic discrimination within the context of design innovations in information access for the blind and low-vision community. Braille discrimination is a complex and poorly understood process that necessitates the coordination of motor control, mechanotransduction, and cognitive-linguistic processing. Despite substantial technological advances and multiple design attempts over the last fifty years, a low-cost, high-fidelity refreshable braille and tactile graphics display has yet to be delivered. Consequently, the blind and low-vision communities are left with limited options for information access. This is amplified by the rapid adoption of graphical user interfaces for human-computer interaction, a move that the blind and low vision community were effectively excluded from. Text-to-speech screen readers lack the ability to convey the nuances necessary for science, technology, engineering, arts, and math education and offer limited privacy for the user. Printed braille and tactile graphics are effective modalities but are time and resource-intensive, difficult to access, and lack real-time rendering. Single- and multiline refreshable braille devices either lack functionality or are extremely cost-prohibitive. Early computational models of mechanotransduction through complex digital skin tissue and the kinematics of the braille reading finger are explored as insight into device design specifications. A use-centered, convergence approach for future designs is discussed in which the design space is defined by both the end-user requirements and the available technology.

Functional mapping of the somatosensory cortex using noninvasive fMRI and touch in awake dogs

Dogs are increasingly used as a model for neuroscience due to their ability to undergo functional MRI fully awake and unrestrained, after extensive behavioral training. Still, we know rather little about dogs' basic functional neuroanatomy, including how basic perceptual and motor functions are localized in their brains. This is a major shortcoming in interpreting activations obtained in dog fMRI. The aim of this preregistered study was to localize areas associated with somatosensory processing. To this end, we touched N = 22 dogs undergoing fMRI scanning on their left and right flanks using a wooden rod. We identified activation in anatomically defined primary and secondary somatosensory areas (SI and SII), lateralized to the contralateral hemisphere depending on the side of touch, and importantly also activation beyond SI and SII, in the cingulate cortex, right cerebellum and vermis, and the sylvian gyri. These activations may partly relate to motor control (cerebellum, cingulate), but also potentially to higher-order cognitive processing of somatosensory stimuli (rostral sylvian gyri), and the affective aspects of the stimulation (cingulate). We also found evidence for individual side biases in a vast majority of dogs in our sample, pointing at functional lateralization of somatosensory processing. These findings not only provide further evidence that fMRI is suited to localize neuro-cognitive processing in dogs, but also expand our understanding of in vivo touch processing in mammals, beyond classically defined primary and secondary somatosensory cortices.

Supplemental vibrissal extensions as an alternative to improve the tactile sensitivity of blind dogs - a preliminary approach investigation

OBJECTIVE

This preliminary study suggests a way to artificially extend vibrissae of blind dogs to assist ambulation and avoiding facial contact with obstacles.

PROCEDURES

Fourteen irreversibly blind dogs had 5-6 mystacial vibrissae on each side of the face supplementally extended by attaching carefully chosen adult pig hairs to them and were subjected to a maze test before and after the procedure. In three of these dogs the test was repeated one more time after all the extensions had fallen off. Collision counts and course times with and without extensions were analyzed and compared. A p-value > 0.05 was considered significant.

RESULTS

Median number of collisions was significantly higher post-extensions (5 IQR 2.25) and after extensions had fallen off (4 IQR 7.50) compared to pre-extensions (1 IQR 1), p = 0.021. Median times were significantly higher pre-extension (25.6 IQR 8.98) and after the extensions had fallen off, compared to the post-extension performance (22.8 IQR 8.55), p = 0.04.

CONCLUSION

Vibrissae play an important role in the tactile perception of blind dogs, and our preliminary results suggest that extending this sensory organ possibly improves obstacle location and their quality of life.

Improving electrotactile communication with a multi-pad electrode under cognitive load

BACKGROUND

Electrotactile systems are compact interfaces that can be used to convey information through the skin by producing a range of haptic sensations. In many applications, however, the user needs to perceive and interpret haptic stimulation while being engaged in parallel activities. Developing methods that ensure reliable recognition of electrotactile messages despite additional cognitive load is, therefore, an important step for the practical application of electrotactile displays.

METHODS

This study investigated if a simple strategy of repeating electrotactile messages can improve message identification during multitasking. Ten participants identified 36 spatiotemporal electrotactile messages delivered through a 3 × 2 pad-matrix electrode placed on the torso while performing a concomitant cognitive task in three conditions: the messages were presented once (No-REP), and each message was repeated three (REP3) and five (REP5) times. The main outcome measure was the success rate (SR) of message identification.

RESULTS

During multitasking, in the No-REP condition, the SR (median (IQR)) dropped to 56.25% (22.62%), demonstrating that the cognitive task decreased performance. However, the SR significantly improved with message repetitions, reaching 72.92% (21.87%) and 81.25% (18.66%) in REP3 and REP5 conditions respectively, without a statistically significant difference between REP3 and REP5.

CONCLUSIONS

Multitasking affected the efficacy of haptic communication, but message repetition was shown to be an effective strategy for improving performance. Additionally, only three repetitions were enough, as an additional increase in the duration of message transmission (5 repetitions) did not lead to further improvement. This study is an important step toward delivering electrotactile communication that can cope with the demands of real-world applications.

Real-time vibrotactile pattern generation and identification using discrete event-driven feedback

This study assesses human identification of vibrotactile patterns by using real-time discrete event-driven feedback. Previously acquired force and bend sensor data from a robotic hand were used to predict movement-type (stationary, flexion, contact, extension, release) and object-type (no object, hard object, soft object) states by using decision tree (DT) algorithms implemented in a field-programmable gate array (FPGA). Six able-bodied humans performed a 2- and 3-step sequential pattern recognition task in which state transitions were signaled as vibrotactile feedback. The stimuli were generated according to predicted classes represented by two frequencies (F1: 80 Hz, F2: 180 Hz) and two magnitudes (M1: low, M2: high) calibrated psychophysically for each participant; and they were applied by two actuators (Haptuators) placed on upper arms. A soft/hard object was mapped to F1/F2; and manipulating it with low/high force was assigned to M1/M2 in the left actuator. On the other hand, flexion/extension movement was mapped to F1/F2 in the right actuator, with movement in air as M1 and during object manipulation as M2. DT algorithm performed better for the object-type (97%) than the movement-type (88%) classification in real time. Participants could recognize feedback associated with 14 discrete-event sequences with low-to-medium accuracy. The performance was higher (76 ± 9% recall, 76 ± 17% precision, 78 ± 4% accuracy) for recognizing any one event in the sequences. The results show that FPGA implementation of classification for discrete event-driven vibrotactile feedback can be feasible in haptic devices with additional cues in the physical context.

Pupil dilation reveals the intensity of touch

Touch is important for many aspects of our daily activities. One of the most important tactile characteristics is its perceived intensity. However, quantifying the intensity of perceived tactile stimulation is not always possible using overt responses. Here, we show that pupil responses can objectively index the intensity of tactile stimulation in the absence of overt participant responses. In Experiment 1 (n = 32), we stimulated three reportedly differentially sensitive body locations (finger, forearm, and calf) with a single tap of a tactor while tracking pupil responses. Tactile stimulation resulted in greater pupil dilation than a baseline without stimulation. Furthermore, pupils dilated more for the more sensitive location (finger) than for the less sensitive location (forearm and calf). In Experiment 2 (n = 20) we extended these findings by manipulating the intensity of the stimulation with three different intensities, here a short vibration, always at the little finger. Again, pupils dilated more when being stimulated at higher intensities as compared to lower intensities. In summary, pupils dilated more for more sensitive parts of the body at constant stimulation intensity and for more intense stimulation at constant location. Taken together, the results show that the intensity of perceived tactile stimulation can be objectively measured with pupil responses - and that such responses are a versatile marker for touch research. Our findings may pave the way for previously impossible objective tests of tactile sensitivity, for example in minimally conscious state patients.

Adults' spatial scaling of tactile maps: Insights from studying sighted, early and late blind individuals

The current study investigated spatial scaling of tactile maps among blind adults and blindfolded sighted controls. We were specifically interested in identifying spatial scaling strategies as well as effects of different scaling directions (up versus down) on participants' performance. To this aim, we asked late blind participants (with visual memory, Experiment 1) and early blind participants (without visual memory, Experiment 2) as well as sighted blindfolded controls to encode a map including a target and to place a response disc at the same spot on an empty, constant-sized referent space. Maps had five different sizes resulting in five scaling factors (1:3, 1:2, 1:1, 2:1, 3:1), allowing to investigate different scaling directions (up and down) in a single, comprehensive design. Accuracy and speed of learning about the target location as well as responding served as dependent variables. We hypothesized that participants who can use visual mental representations (i.e., late blind and blindfolded sighted participants) may adopt mental transformation scaling strategies. However, our results did not support this hypothesis. At the same time, we predicted the usage of relative distance scaling strategies in early blind participants, which was supported by our findings. Moreover, our results suggested that tactile maps can be scaled as accurately and even faster by blind participants than by sighted participants. Furthermore, irrespective of the visual status, participants of each visual status group gravitated their responses towards the center of the space. Overall, it seems that a lack of visual imagery does not impair early blind adults' spatial scaling ability but causes them to use a different strategy than sighted and late blind individuals.

A wirelessly programmable, skin-integrated thermo-haptic stimulator system for virtual reality

Sensations of heat and touch produced by receptors in the skin are of essential importance for perceptions of the physical environment, with a particularly powerful role in interpersonal interactions. Advances in technologies for replicating these sensations in a programmable manner have the potential not only to enhance virtual/augmented reality environments but they also hold promise in medical applications for individuals with amputations or impaired sensory function. Engineering challenges are in achieving interfaces with precise spatial resolution, power-efficient operation, wide dynamic range, and fast temporal responses in both thermal and in physical modulation, with forms that can extend over large regions of the body. This paper introduces a wireless, skin-compatible interface for thermo-haptic modulation designed to address some of these challenges, with the ability to deliver programmable patterns of enhanced vibrational displacement and high-speed thermal stimulation. Experimental and computational investigations quantify the thermal and mechanical efficiency of a vertically stacked design layout in the thermo-haptic stimulators that also supports real-time, closed-loop control mechanisms. The platform is effective in conveying thermal and physical information through the skin, as demonstrated in the control of robotic prosthetics and in interactions with pressure/temperature-sensitive touch displays.

Reach-to-Grasp and tactile discrimination task: A new task for the study of sensory-motor learning

Although active touch in rodents arises from the forepaws as well as whiskers, most research on active touch only focuses on whiskers. This results in a paucity of tasks designed to assess the process of active touch with a forepaw. We develop a new experimental task, the Reach-to-Grasp and Tactile Discrimination task (RGTD task), to examine active touch with a forepaw in rodents, particularly changes in processes of active touch during motor skill learning. In the RGTD task, animals are required to (1) extend their forelimb to an object, (2) grasp the object, and (3) manipulate the grasped object with the forelimb. The animals must determine the direction of the manipulation based on active touch sensations arising during the period of the grasping. In experiment 1 of the present study, we showed that rats can learn the RGTD task. In experiment 2, we confirmed that the rats are capable of reversal learning of the RGTD task. The RGTD task shared most of the reaching movements involved with conventional forelimb reaching tasks. From the standpoint of a discrimination task, the RGTD task enables rigorous experimental control, for example by removing bias in the stimulus-response correspondence, and makes it possible to utilize diverse experimental procedures that have been difficult in prior tasks.

Tactile memory impairments in younger and older adults

Human tactile memory allows us to remember and retrieve the multitude of somatosensory experiences we undergo in everyday life. An unsolved question is how tactile memory mechanisms change with increasing age. We here use the ability to remember fine-grained tactile patterns passively presented to the fingertip to investigate age-related changes in tactile memory performance. In experiment 1, we varied the degree of similarity between one learned and several new tactile patterns to test on age-related changes in the "uniqueness" of a stored tactile memory trace. In experiment 2, we varied the degree of stimulus completeness of both known and new tactile patterns to test on age-related changes in the weighting between known and novel tactile information. Results reveal that older adults show only weak impairments in both precision and bias of tactile memories, however, they show specific deficits in reaching peak performance > 85% in both experiments. In addition, both younger and older adults show a pattern completion bias for touch, indicating a higher weighting of known compared to new information. These results allow us to develop new models on how younger and older adults store and recall tactile experiences of the past, and how this influences their everyday behavior.

Virtual social grooming in macaques and its psychophysiological effects

Allogrooming is a widespread, pervasive activity among non-human primates. Besides its hygienic function, it is thought to be instrumental in maintaining social bonds and establishing hierarchical structures within groups. However, the question arises as to whether the physiological and social benefits derived from social touch stem directly from body stimulation, or whether other mechanisms come into play. We address this question by analyzing an elaborate social behavior that we observed in two adult male macaques. This behavior demonstrates the existence of a persistent motivation to interact through a form of simulated grooming, as the animals were housed in adjacent enclosures separated by a glass panel preventing direct tactile contact. We find that such virtual grooming produces similar physiological sensations and social effects as allogrooming. We suggest that this behavior engages affective and reward brain circuits to the same extent as real social touch, and that this is probably achieved through high level processes similar to those involved in bodily illusions or synaesthetic phenomena previously described in humans. This observation reveals the unsuspected capacity of non-human primates to invent alternative, quasi-symbolic strategies to obtain effects similar to those provided by direct bodily interaction, which are so important for maintaining social bonds.

Developmental changes of bodily self-consciousness in adolescent girls

The body and the self change markedly during adolescence, but how does bodily self-consciousness, the pre-reflexive experience of being a bodily subject, change? We addressed this issue by studying embodiment towards virtual avatars in 70 girls aged 10-17 years. We manipulated the synchrony between participants' and avatars' touch or movement, as well as the avatar visual shape or size relative to each participant's body. A weaker avatar's embodiment in case of mismatch between the body seen in virtual reality and the real body is indicative of a more robust bodily self-consciousness. In both the visuo-tactile and the visuo-motor experiments, asynchrony decreased ownership feeling to the same extent for all participants, while the effect of asynchrony on agency feeling increased with age. In the visuo-tactile experiment, incongruence in visual appearance did not affect agency feeling but impacted ownership, especially in older teenage girls. These findings highlight the higher malleability of bodily self-consciousness at the beginning of adolescence and suggest some independence between body ownership and agency.

Alpha interbrain synchrony during mediated interpersonal touch

Interpersonal touch plays a crucial role in human communication, development, and wellness. Mediated interpersonal touch (MIT), a technology to distance or virtually simulated interpersonal touch, has received significant attention to counteract the negative consequences of touch deprivation. Studies investigating the effectiveness of MIT have primarily focused on self-reporting or behavioral correlates. It is largely unknown how MIT affects neural processes such as interbrain functional connectivity during human interactions. Given how users exchange haptic information simultaneously during interpersonal touch, interbrain functional connectivity provides a more ecologically valid way of studying the neural correlates associated with MIT. In this study, a palm squeeze task is designed to examine interbrain synchrony associated with MIT using EEG-based hyperscanning methodology. The phase locking value (PLV) index is used to measure interbrain synchrony. Results demonstrate that MIT elicits a significant increase in alpha interbrain synchronization between participants' brains. Especially, there was a significant difference in the alpha PLV indices between no MIT and MIT conditions in the early stage (130-470 ms) of the interaction period (t-test, p < 0.05). Given the role that alpha interbrain synchrony plays during social interaction, a significant increase in PLV index during MIT interaction seems to indicate an effect of social coordination. The findings and limitations of this study are further discussed, and perspectives on future research are provided.

To touch or to be touched? comparing appraisal of vicarious execution and reception of interpersonal touch

Unmyelinated C-Tactile (CT) fibres are activated by caress-like touch, eliciting a pleasant feeling that decreases for static and faster stroking. Previous studies documented this effect also for vicarious touch, hypothesising simulation mechanisms driving the perception and appreciation of observed interpersonal touch. Notably, less is known about appreciation of vicarious execution of touch, that is as referred to the one giving gentle touch. To address this issue, 53 healthy participants were asked to view and rate a series of videoclips displaying an individual being touched by another on hairy (i.e., hand dorsum) or glabrous (i.e., palm) skin sites, with touch being delivered at CT-optimal (5 cm/s) or non-CT optimal velocities (0 cm/s or 30 cm/s). Following the observation of each clip, participants were asked to rate self-referred desirability and model-referred pleasantness of vicarious touch for both executer (toucher-referred) and receiver (touchee-referred). Consistent with the CT fibres properties, for both self-referred desirability and model-referred pleasantness judgements of vicarious touch execution and reception, participants provided higher ratings for vicarious touch delivered at CT-optimal than other velocities, and when observed CT-optimal touch was delivered to the hand-dorsum compared to the palm. However, higher ratings were attributed to vicarious reception compared to execution of CT-optimal touch. Notably, individual differences in interoceptive trusting and attitude to interpersonal touch were positively correlated with, respectively, toucher- and touchee-related overall appraisal ratings of touch. These findings suggest that the appreciation of both toucher- and touchee-referred vicarious touch is specifically attuned to CT-optimal touch, even though they might rely on different neurocognitive mechanisms to understand affective information conveyed by interpersonal tactile interactions.

Enhancing touch sensibility with sensory electrical stimulation and sensory retraining

A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures-haptically rendered by a robotic device and that differed in their spatial period-while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance-assessed by the probability of correct responses-before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8-13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.

Spike timing-based coding in neuromimetic tactile system enables dynamic object classification

Rapid processing of tactile information is essential to human haptic exploration and dexterous object manipulation. Conventional electronic skins generate frames of tactile signals upon interaction with objects. Unfortunately, they are generally ill-suited for efficient coding of temporal information and rapid feature extraction. In this work, we report a neuromorphic tactile system that uses spike timing, especially the first-spike timing, to code dynamic tactile information about touch and grasp. This strategy enables the system to seamlessly code highly dynamic information with millisecond temporal resolution on par with the biological nervous system, yielding dynamic extraction of tactile features. Upon interaction with objects, the system rapidly classifies them in the initial phase of touch and grasp, thus paving the way to fast tactile feedback desired for neuro-robotics and neuro-prosthetics.