Hello from the other side: Robust contralateral interference in tactile detection.

Touch is unique among the sensory modalities in that our tactile receptors are spread across the body surface and continuously receive different inputs at the same time. These inputs vary in type, properties, relevance according to current goals, and, of course, location on the body. Sometimes, they must be integrated, and other times set apart and distinguished. Here, we investigate how simultaneous stimulation to different body sites affects tactile cognition. Specifically, we characterized the impact of irrelevant tactile sensations on tactile change detection. To this end, we embedded detection targets amidst ongoing performance, akin to the conditions encountered in everyday life, where we are constantly confronted with new events within ongoing stimuli. In the set of experiments presented here, participants detected a brief intensity change (.04 s) within an ongoing vibrotactile stimulus (1.6 s) that was always presented in a constantly attended location. The intensity change (i.e., the detection target) varied parametrically, from hardly detectable to easily detectable. In half of the trials, irrelevant ongoing stimulation was simultaneously presented to a site across the body midline, but participants were instructed to ignore it. In line with previous bimanual studies employing brief onset targets, we document robust interference on performance due to the irrelevant stimulation at each of the measured body sites (homologous and nonhomologous fingers, and the contralateral ankle). After describing this basic phenomenon, we further examine the conditions under which such interference occurs in three additional tasks. In each task, we honed in on a different aspect of the stimulation protocol (e.g., hand distance, the strength of the irrelevant stimulation, the detection target itself) in order to better understand the principles governing the observed interference effects. Our findings suggest a minimal role for exogenous attentional capture in producing the observed interference effects (Exp. 2), and a principled distribution of attentional resources or sensory integration between body sides (Exps. 3, 4). In our last study (Exp. 4), we presented bilateral tactile targets of varying intensities to both the relevant and irrelevant stimulation sites. We then characterized the degree to which the irrelevant stimulation is also processed. Our results-that participants' perception of target intensity is always proportional to the combined bilateral signal-suggest that both body sites are equally weighed and processed despite clear instructions to attend only the target site. In light of this observation and participants' inability to use selection processes to guide their perception, we propose that bilateral tactile inputs are automatically combined, quite possibly early in the hierarchy of somatosensory processing.

Identification of areas of the brain activated by active stimulation in hairless skin.

In the past few decades, neuroscientists have studied the physiological basis of pleasant touch. Unmyelinated low-threshold mechanoreceptors are central to the study of the physiological basis of pleasant touch. Research on pleasant stimuli has mostly focused on passive stimuli, and the brain activation sites for active pleasant stimuli are not clear. Therefore, the purpose of this study was to identify brain activation sites during active pleasant stimulation of hairless skin using functional magnetic resonance imaging. Forty-two healthy subjects aged 19 years or older were asked to actively grasp in five stimulus tasks. The comfort and sensations that occurred during the tasks were investigated using a questionnaire. Significant activation was found in the middle frontal gyrus when the hair ball and slime ball were grasped, while there was significant activation in the amygdala when grasping a squeeze ball compared to the tennis ball. In a questionnaire survey of the subjects, there was a significant difference in the comfort score between the tennis ball and the squeeze ball, but no significant correlation was found between the comfort scores and the brain sites of activation. Therefore, although active stimulation with the squeeze ball significantly activated the amygdala, it was not clear that the amygdala was significantly activated by active pleasant stimulation. In the future, it will be necessary to investigate the texture of the squeeze ball in more detail, and to increase the number of subjects for further study.

Infants' sex affects neural responses to affective touch in early infancy.

Social touch is closely related to the establishment and maintenance of social bonds in humans, and the sensory brain circuit for gentle brushing is already active soon after birth. Brain development is known to be sexually dimorphic, but the potential effect of sex on brain activation to gentle touch remains unknown. Here, we examined brain activation to gentle skin stroking, a tactile stimulation that resembles affective or social touch, in term-born neonates. Eighteen infants aged 11-36 days, recruited from the FinnBrain Birth Cohort Study, were included in the study. During natural sleep, soft brush strokes were applied to the skin of the right leg during functional magnetic resonance imaging (fMRI) at 3 cm/s velocity. We examined potential differences in brain activation between males (n = 10) and females (n = 8) and found that females had larger blood oxygenation level dependent (BOLD) responses (brushing vs. rest) in bilateral orbitofrontal cortex (OFC), right ventral striatum and bilateral inferior striatum, pons, and cerebellum compared to males. Moreover, the psychophysiological interactions (PPI) analysis, setting the left and right OFC as seed regions, revealed significant differences between males and females. Females exhibited stronger PPI connectivity between the left OFC and posterior cingulate or cuneus. Our work suggests that social touch neural responses are different in male and female neonates, which may have major ramifications for later brain, cognitive, and social development. Finally, many of the sexually dimorphic brain responses were subcortical, not captured by surface-based neuroimaging, indicating that fMRI will be a relevant technique for future studies.

On the Correlation Between Tactile Stimulation and Pleasantness.

Several studies in the affective haptics research field showed the potential of using haptic technology to convey emotions in remote communications. In this context, it is of interest to simplify the haptic feedback without altering the informative content of the stimulus, with a two-fold advantage. On one side, it would allow the development of affective haptic devices whose technological complexity is limited, hence more compatible with wearability and portability requirements. On the other side, having a simplified set of stimuli would decrease the amount of data to be transmitted, thus improving the overall quality of remote haptic interactions. In this work, we investigated the correlation between the parameters regulating a caress-like stimulation and the perceived pleasantness. This was done by means of two experiments, in which we asked subjects to adjust the temperature and the motion velocity of a set of stimuli in order to find the most pleasant combination. Results indicated that subjects preferred different values of temperature and velocity of the stimulus depending on the proposed tactile stimulation. A small difference in the pleasantness ratings was observed between caresses provided with linear movements and those given as discrete sequences of taps. In particular, participants preferred linear movements set at 34.5 °C and 3.4 cms-1. As regards caress-like stimuli provided with discrete sequences of taps, the preferred temperature and velocity were 33.2 °C and 2.9 cms-1, respectively. The presence of vibration had a little effect on the perceived pleasantness.

[Characterization of brain deactivations elicited by transient painful and tactile stimuli using functional MRI].

The aim of the present study was to explore the specific pattern of brain deactivation elicited by painful stimuli, in contrast with that elicited by tactile stimuli. Functional magnetic resonance imaging (fMRI) data were collected from 62 healthy subjects under painful and tactile stimuli with varying intensities. The brain deactivations under different conditions were identified using the general linear model. Two-way analysis of variance (ANOVA) was performed to test whether there was a significant interaction between perceived stimulus intensity (factor 1: high intensity, low intensity) and stimulus modality (factor 2: pain, touch) on the brain deactivations. The results showed that there were significant interactions between stimulus intensity and stimulus modality on the deactivations of left medial superior frontal gyrus, left middle occipital gyrus, left superior frontal gyrus and right middle occipital gyrus (P < 0.05, Cluster-level FWE). The deactivations induced by painful stimuli with low perceived intensity (ß = -3.38 ± 0.52) were significantly stronger than those induced by painful stimuli with high perceived intensity (ß = -1.22 ± 0.54) (P < 0.001), whereas the differences between the deactivations induced by tactile stimuli with different perceived intensities were not statistically significant. In addition, there were no significant differences between the deactivations elicited by painful and tactile stimuli with the same stimulus intensities. These results suggest that there is a specific relationship between the deactivations induced by painful stimuli in multiple brain regions (such as the left medial superior frontal gyrus) and the stimulus intensity, providing evidence for a deeper understanding of the brain mechanisms underlying pain perception.

I wanna hold your hand: Handholding is preferred over gentle stroking for emotion regulation.

Social touch is an important form of interpersonal emotion regulation. In recent years, the emotion regulation effects of two types of touch have been studied extensively: handholding and stroking (specifically of skin with C-tactile afferents on the forearm, i.e. C-touch). While some studies compare their effectiveness, with mixed results, no study to date has examined which type of touch is subjectively preferred. Given the potential bidirectional communication provided by handholding, we hypothesized that to regulate intense emotions, participants would prefer handholding. In four pre-registered online studies (total N = 287), participants rated handholding and stroking, presented in short videos, as emotion regulation methods. Study 1 examined touch reception preference in hypothetical situations. Study 2 replicated Study 1 while also examining touch provision preferences. Study 3 examined touch reception preferences of participants with blood/injection phobia in hypothetical injection situations. Study 4 examined types of touch participants who have recently given birth recalled receiving during childbirth and their hypothetical preferences. In all studies, participants preferred handholding over stroking; participants who have recently given birth reported receiving handholding more than stroking. This was especially evident in Studies 1-3 in emotionally intense situations. These results demonstrate that handholding is preferred over stroking as a form of emotion regulation, especially in intense situations, and support the importance of two-way sensory communication for emotion regulation via touch. We discuss the results and possible additional mechanisms, including top-down processing and cultural priming.

The dynamic behavior of skin in response to vibrating touch stimuli affects tactile perception.

BACKGROUND: The tactile perceptions arising on the skin mediate representations of the body and perceptions of the external physical world. Thus, these tactile sensations greatly impact our lives. Although tactile perception is caused by skin deformation, few studies have investigated the contribution of skin physical properties to tactile perception because the skin deformation in response to mechanical stimuli is difficult to measure in real time. In this study, we investigated how the skin deforms in response to externally applied mechanical stimuli and the effect of skin deformation on tactile perception. MATERIALS AND METHODS: Tactile perception was assessed using psychophysical methods. A suction device was used to measure skin deformation in response to mechanical stimuli while assessing tactile perception. The relationship between skin deformation and tactile perception was investigated. RESULTS: Individuals show different skin deformation behavior in response to stimuli of the same intensity, and the amount of skin deformation affects the perceived pressure induced by suction stimulation. Furthermore, when the amount of skin deformation is small, tactile perception becomes more difficult, and the ease of tactile perception varies. CONCLUSION: We argue that dynamic skin behavior is an important factor in tactile perception. Focusing on skin physical characteristics from a constructivist perspective of complex tactile perception may lead to improved tactile communication perception through the control of skin physical properties and realistic tactile presentation in remote environments.

Hand and face somatotopy shown using MRI-safe vibrotactile stimulation with a novel soft pneumatic actuator (SPA)-skin interface.

The exact somatotopy of the human facial representation in the primary somatosensory cortex (S1) remains debated. One reason that progress has been hampered is due to the methodological challenge of how to apply automated vibrotactile stimuli to face areas in a manner that is: (1) reliable despite differences in the curvatures of face locations; and (2) MR-compatible and free of MR-interference artefacts when applied in the MR head-coil. Here we overcome this challenge by using soft pneumatic actuator (SPA) technology. SPAs are made of a soft silicon material and can be in- or deflated by means of airflow, have a small diameter, and are flexible in structure, enabling good skin contact even on curved body surfaces (as on the face). To validate our approach, we first mapped the well-characterised S1 finger layout using this novel device and confirmed that tactile stimulation of the fingers elicited characteristic somatotopic finger activations in S1. We then used the device to automatically and systematically deliver somatosensory stimulation to different face locations. We found that the forehead representation was least distant from the representation of the hand. Within the face representation, we found that the lip representation is most distant from the forehead representation, with the chin represented in between. Together, our results demonstrate that this novel MR compatible device produces robust and clear somatotopic representational patterns using vibrotactile stimulation through SPA-technology.

Velocity-tuning of somatosensory EEG predicts the pleasantness of gentle caress.

Numerous studies have established an inverted u-shaped effect between the velocity of a caress and its pleasantness and linked this effect to the C-tactile (CT) system considered central for physical and mental health. This study probed whether cortical somatosensory representations predict and explain the inverted u-shaped effect and addressed associated individual differences. Study participants (N = 90) rated the pleasantness of stroking at varying velocities while their electroencephalogram was being recorded. An analysis across all participants replicated a preference for intermediate velocities, while a cluster analysis discriminated individuals who preferred slow (N = 43) from those who preferred fast stroking (N = 47). In both groups, intermediate velocities maximized amplitudes of a somatosensory event-related potential referred to as sN400, in line with the average rating effect. By contrast, group differences emerged in how velocity modulated a late positive potential (LPP) and Rolandic power. Notably, both the sN400 and the velocity-tuning of LPP and Rolandic power predicted the participants' pleasantness ratings. Participants were more likely to prefer slow over fast stroking the better their LPP and Rolandic power differentiated between different velocities. Together, these results shed light on the complexity of tactile affect. They corroborate an average preference for intermediate velocities that relates to largely shared effects of CT-targeted touch on the activity of somatosensory cortex. Additionally, they identify individual differences as a function of how accurately somatosensory cortex represents the velocity of peripheral input and suggest these differences are relevant for the extent to which individuals pursue beneficial, CT-targeted touch.

Stroking trajectory shapes velocity effects on pleasantness and other touch percepts.

Research has identified an inverted u-shaped relationship between the pleasantness of arm stroking and stroking velocity. However, the generalizability of this relationship is questionable as much of the work relied on the rotary tactile stimulator (RTS), which strokes skin with force varying along an arc and confounds stimulus velocity with duration. We explored how these parameters shape the subjective evaluation of touch. In Study 1, one group of participants was stroked by the RTS, while two other groups were stroked by a new robot capable of different stroking trajectories. Participants were stroked at five velocities and rated pleasantness, humanness, intensity, and roughness. In Study 2, participants were stroked by the new robot imitating the trajectory of the RTS exactly, imitating it while controlling stimulus duration, or moving linearly or ovally with both constant force and duration. Participants rated pleasantness and humanness. Although stroke velocity was related to both pleasantness and humanness in an inverted u-shaped manner, stimulus trajectory modulated this relationship and the association between velocity and the other ratings. Together, our results clearly link stroking velocity to the perception of touch but highlight that this relationship is shaped by other physical parameters including touch duration and spatial pattern. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

A neurobiological evaluation of soft touch training for patients with skin-picking disorder.

BACKGROUND: Individuals with skin-picking disorder (SPD) display reduced neural sensitivity to slow/soft touch. This functional magnetic resonance imaging (fMRI) study investigated the effects of Soft Touch Training (STT) on neural correlates of touch processing and SPD symptoms. METHOD: Females with a primary diagnosis of SPD (n = 57) were randomly assigned to receive either four weeks of STT (guided soft brushing of selected skin regions) or Progressive Muscle Relaxation (PMR) training (guided tensing and relaxing of selected muscle regions). The app-assisted intervention consisted of 15-minute daily training sessions at home. Before and after the four-week intervention, the two groups participated in a standardized tactile stimulation procedure during fMRI (affective vs nonaffective touch of the forearm). Intervention-based changes in subjective and neural responses to the tactile stimulation as well as SPD severity were compared between the groups. RESULTS: STT increased the pleasantness ratings for (affective) touch administered during fMRI, which was accompanied by decreased activation in the parietal operculum (PO) and supramarginal gyrus (SMG), as well as increased PO-SMG connectivity. These findings possibly reflect normalized affective touch processing due to STT. Both interventions (STT and PMR) reduced SPD severity. CONCLUSIONS: This study demonstrated that a brief app-assisted touch training can change the experience of receiving touch from others and the associated brain activity and connectivity. Adaptations of the training relating to duration/ frequency of sessions might enhance its effectiveness.

Modeling affective touch pleasantness across skin types at the individual level reveals a reliable and stable basic function.

Touch is perceived most pleasant when delivered at velocities known to optimally activate the C-tactile afferent system. At the group level, pleasantness ratings of touch delivered at velocities in the range between 0.3 and 30 cm/s follow an inverted-U shape curve, with maximum pleasantness between 1 and 10 cm/s. However, the prevalence, reliability, and stability of this function at the individual level and across skin types based on hair density remains unknown. Here, we tested a range of seven velocities (0.3, 1, 3, 6, 9, 18, and 27 cm/s) delivered with a soft brush, on both hairy (forearm and dorsal hand) and nonhairy skin (palm) in 123 participants. Our results suggest that the relationship between pleasantness and velocity of touch is significantly best described by a negative quadratic model at the individual level in the majority of participants both on hairy (67.1%) and nonhairy (62.6%) skin, a larger extent than previously reported. Higher interoceptive accuracy and self-reported depression were related to a better fit of the quadratic model and the steepness of the curve, respectively. The prevalence of the quadratic model at the individual level was stable across body sites (62.6%, experiment 1), across two experimental sessions (73%-78%, experiment 2), and regardless of the number of repetitions of each velocity (experiment 3). Thus, the individual perception of tactile pleasantness follows a characteristic velocity-dependent function across skin types and shows trait characteristics. Future studies can investigate further the possibility to use affective touch as a behavioral biomarker for mental health disorders.NEW & NOTEWORTHY Touch is perceived as most pleasant when delivered at slow, caress-like velocities, known to activate C-tactile afferents. At the group level, tactile pleasantness and velocity of touch show a reliable pattern of relationship on hairy skin. Here, we found that the perception of tactile pleasantness follows a consistent pattern also at the individual level, across skin types and testing sessions. However, individual differences in interoceptive abilities and self-reported depression do play a role.

Vicarious ratings of self vs. other-directed social touch in women with and recovered from Anorexia Nervosa.

Anorexia Nervosa (AN) is an eating pathology characterized by restricted eating, body image distortions and impaired socio-cognitive abilities. Altered responses to affective touch-a pleasant interoceptive stimulus hypothesised to involve activation of the C-Tactile (CT) system, may contribute to the aetiology and maintenance of this disorder. Here, we investigated whether third-party social touch vicarious ratings of different body sites at CT-optimal vs. non-CT optimal velocities differed in women with and recovered from AN (RAN) and healthy controls (HCs). Thirty-five HCs, 27 AN and 29 RAN provided pleasantness ratings for two different tasks designed to probe expectations of how touch is perceived by self (self-directed touch) vs. others (other-directed touch). Findings revealed that both clinical groups, compared to HCs, did not differ in their pleasantness ratings to touch for another but when evaluating touch for self, both clinical groups rated CT-optimal touch as less pleasant than HCs. These findings suggest that AN and RAN women demonstrate an atypical vicarious pleasantness response to affective touch involving self, but not others. Novel therapeutic approaches that help anorexics to better interpret or improve tolerance of affective tactile experiences involving the self may be an important addition to current standard treatments.

Acute tryptophan depletion alters affective touch perception.

RATIONALE: Affiliative 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. OBJECTIVES: The aim of the present study was to determine the effect of acutely lowering central serotonin levels on perceptions of CT-targeted affective touch. METHODS: In 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. RESULTS: ATD 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. CONCLUSIONS: These findings are consistent with previous reports that depletion of central serotonin levels modulates neural and behavioural responsiveness to appetitive sensory signals.

The effects of locomotion on sensory-evoked haemodynamic responses in the cortex of awake mice.

Investigating neurovascular coupling in awake rodents is becoming ever more popular due, in part, to our increasing knowledge of the profound impacts that anaesthesia can have upon brain physiology. Although awake imaging brings with it many advantages, we still do not fully understand how voluntary locomotion during imaging affects sensory-evoked haemodynamic responses. In this study we investigated how evoked haemodynamic responses can be affected by the amount and timing of locomotion. Using an awake imaging set up, we used 2D-Optical Imaging Spectroscopy (2D-OIS) to measure changes in cerebral haemodynamics within the sensory cortex of the brain during either 2 s whisker stimulation or spontaneous (no whisker stimulation) experiments, whilst animals could walk on a spherical treadmill. We show that locomotion alters haemodynamic responses. The amount and timing of locomotion relative to whisker stimulation is important, and can significantly impact sensory-evoked haemodynamic responses. If locomotion occurred before or during whisker stimulation, the amplitude of the stimulus-evoked haemodynamic response was significantly altered. Therefore, monitoring of locomotion during awake imaging is necessary to ensure that conclusions based on comparisons of evoked haemodynamic responses (e.g., between control and disease groups) are not confounded by the effects of locomotion.

Understanding sex differences in affective touch: Sensory pleasantness, social comfort, and precursive experiences.

Although previous research revealed sex differences in affective touch, the implicated processes and the manner in which men and women differ have been left uncertain. Here we addressed this issue in two studies examining sensory pleasure, interpersonal comfort, and touch motivators. Study 1 comprised a series of lab-based experiments in which a robot stroked 214 participants (half female) at five different velocities modulating the activity of C-tactile afferents thought to support tactile pleasantness. Average pleasantness ratings followed velocity with the typical inverted u-shape similarly in both sexes. In Study 2, 260 participants (half female) completed an online survey. Here, women were more likely than men to express touch comfort with less familiar or unknown individuals, had a greater preference for touch with other women, and felt more comfortable giving and receiving touch to the forearm. Additionally, when describing how their own experiences might motivate others to touch them affectively, women produced more negative descriptions than men. Together, these results show that, while the sexes compare in a touch's sensory pleasantness, they differ in their preceding affective experiences and how they value touch at a higher-order social level. This agrees with extant research on negative affect and stress and suggests that affective touch may be a more relevant coping mechanism for women than for men.

A novel stimulator to investigate the tuning of multi-whisker responsive neurons for speed and the direction of global motion: Contact-sensitive moving stimulator for multi-whisker stimulation.

BACKGROUND: The rodent vibrissal (whisker) systcnsorimotor integration and active tactile sensing. Experiments on the vibrissal system often require highly repeatable stimulation of multiple whiskers and the ability to vary stimulation parameters across a wide range. The stimulator must also be easy to position and adjust. Developing a multi-whisker stimulation system that meets these criteria remains challenging. NEW METHOD: We describe a novel multi-whisker stimulator to assess neural selectivity for the direction of global motion. The device can generate repeatable, linear sweeps of tactile stimulation across the whisker array in any direction and with a range of speeds. A fiber optic beam break detects the interval of whisker contact as the stimulator passes through the array. RESULTS: We demonstrate the device's function and utility by recording from a small number of multi-whisker-responsive neurons in the trigeminal brainstem. Neurons had higher firing rates in response to faster stimulation speeds; some also exhibited strong direction-of-motion tuning. COMPARISON WITH EXISTING METHODS: The stimulator complements more standard piezo-electric stimulators, which offer precise control but typically stimulate only single whiskers, require whisker trimming, and travel through small angles. It also complements non-contact methods of stimulation such as air-puffs and electromagnetic-induced stimulation. Tradeoffs include stimulation speed and frequency, and the inability to stimulate whiskers individually. CONCLUSIONS: The stimulator could be used - in either anesthetized or awake, head-fixed preparations - as an approach to studying global motion selectivity of multi-whisker sensitive neurons at multiple levels of the vibrissal-trigeminal system.

Remote and Selective Control of Astrocytes by Magnetomechanical Stimulation.

Astrocytes play crucial and diverse roles in brain health and disease. The ability to selectively control astrocytes provides a valuable tool for understanding their function and has the therapeutic potential to correct dysfunction. Existing technologies such as optogenetics and chemogenetics require the introduction of foreign proteins, which adds a layer of complication and hinders their clinical translation. A novel technique, magnetomechanical stimulation (MMS), that enables remote and selective control of astrocytes without genetic modification is described here. MMS exploits the mechanosensitivity of astrocytes and triggers mechanogated Ca2+ and adenosine triphosphate (ATP) signaling by applying a magnetic field to antibody-functionalized magnetic particles that are targeted to astrocytes. Using purpose-built magnetic devices, the mechanosensory threshold of astrocytes is determined, a sub-micrometer particle for effective MMS is identified, the in vivo fate of the particles is established, and cardiovascular responses are induced in rats after particles are delivered to specific brainstem astrocytes. By eliminating the need for device implantation and genetic modification, MMS is a method for controlling astroglial activity with an improved prospect for clinical application than existing technologies.

Brain activation related to the tactile perception of touching ridged texture using fingers.

BACKGROUND: Humans can recognize the physical properties of objects by touching them, even when vision is unavailable. Tactile perception is important for humans in interacting with the environment. The triangular ridged textures are usually added to surface to improve the grip reliability of products, but the sharp edge of triangular ridge induces sharp and uncomfortable feeling. MATERIALS AND METHODS: To study the effect of the edge shape of triangular ridged texture on brain activity, functional magnetic resonance imaging technique was used to obtain the blood oxygen level-dependent (BOLD) signal of subjects during the touching of textured surfaces. Samples with sharp, round, and flat shape ridged textures were chosen as the tactile stimulus. RESULTS: The contralateral postcentral gyrus, the precentral gyrus, the inferior parietal lobule, and the supramarginal gyrus, corresponding with the functional regions of the primary somatosensory cortex (SI), the secondary somatosensory cortex (SII), and the primary motor cortex (MI) were related to the perception of three shape ridged textures. The main brain activation located in the postcentral gyrus and the SI. The tactile information of three shape ridged textures was received by Brodmann area (BA) 3 of the SI, and then inputted to BA 2 of the SI, the further tactile discrimination of shape of ridged textures was involved in BA40 of the SII. The intensity, the areas, and the percent signal change (PSC) of brain activation that were evoked by different shape ridged textures were related to the geometric structures of the ridged textures. The more complex the geometric structures of texture are, the larger the intensity, the area, and the PSC in brain activation are. The negative BOLD responses of the ipsilateral sensory cortex that were evoked by the flat ridged texture indicated the ipsilateral neuronal inhibition within the sensory systems. The bilateral precuneus, the superior parietal gyrus, and the inferior parietal gyrus, corresponding with the functional areas of the SII (BA40) and the SSA(BA7), were involved in the tactile discriminate of the differences in shapes of ridged textures. The differences in brain activation were related to the differences in geometric structures of the ridged texture. The larger the differences in geometric structure of texture are, the larger the differences in brain activation are. This study revealed the activated location of brain related to the tactile stimulation of different edge shape of ridged textures and the relationship between the geometric structures of ridged texture and brain activities. This research contributes to optimize surface tactile characteristics on products, especially effective surface textures design for good grip.

Data-Driven Sparse Skin Stimulation Can Convey Social Touch Information to Humans.

During social interactions, people use auditory, visual, and haptic cues to convey their thoughts, emotions, and intentions. Due to weight, energy, and other hardware constraints, it is difficult to create devices that completely capture the complexity of human touch. Here we explore whether a sparse representation of human touch is sufficient to convey social touch signals. To test this we collected a dataset of social touch interactions using a soft wearable pressure sensor array, developed an algorithm to map recorded data to an array of actuators, then applied our algorithm to create signals that drive an array of normal indentation actuators placed on the arm. Using this wearable, low-resolution, low-force device, we find that users are able to distinguish the intended social meaning, and compare performance to results based on direct human touch. As online communication becomes more prevalent, such systems to convey haptic signals could allow for improved distant socializing and empathetic remote human-human interaction.