BACKGROUND: Tactile sensitivity and sensory overload in ADHD are well-documented in clinical-, self-, and parent- reports, but empirical evidence is scarce and ambiguous and focuses primarily on children. Here, we compare both empirical and self-report tactile sensitivity and ADHD symptomatology in adults with ADHD and neurotypical controls. We evaluate whether tactile sensitivity and integration is more prevalent in ADHD and whether it is related to ADHD symptom severity.
METHODS: Somatosensory evoked potential (SEP) amplitudes were measured in 27 adults with ADHD and 24 controls during four conditions (rest, stroking of the own arm, stroking of the arm by a researcher, and stroking of an object). Participants also filled out questionnaires on tactile sensitivity and ADHD symptoms and performed a Qb-test as an objective measure of ADHD symptom severity.
RESULTS: Participants with ADHD self-reported greater tactile sensitivity and ADHD symptom severity than controls and received higher scores on the Qb-test. These values correlated with one another. ADHD participants showed lower tolerable threshold for electrical radial nerve stimulus, and greater reduction in cortical SEP amplitudes during additional tactile stimuli which was correlated with ADHD symptoms.
CONCLUSIONS: We find that ADHD symptomatology and touch sensitivity are directly linked, using both self-reports and experimental measures. We also find evidence of tactile sensory overload in ADHD, and an indication that this is linked to inattention specifically. Tactile sensitivity and sensory overload impact the functioning and life quality of many people with ADHD, and clinicians should consider this when treating their patients.

In tactile sensing, decoding the journey from afferent tactile signals to efferent motor commands is a significant challenge primarily due to the difficulty in capturing population-level afferent nerve signals during active touch. This study integrates a finite element hand model with a neural dynamic model by using microneurography data to predict neural responses based on contact biomechanics and membrane transduction dynamics. This research focuses specifically on tactile sensation and its direct translation into motor actions. Evaluations of muscle synergy during in -vivo experiments revealed transduction functions linking tactile signals and muscle activation. These functions suggest similar sensorimotor strategies for grasping influenced by object size and weight. The decoded transduction mechanism was validated by restoring human-like sensorimotor performance on a tendon-driven biomimetic hand. This research advances our understanding of translating tactile sensation into motor actions, offering valuable insights into prosthetic design, robotics, and the development of next-generation prosthetics with neuromorphic tactile feedback.

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.

Tactile and pain perception are essential for biological skin to interact with the external environment. This complex interplay of sensations allows for the detection of potential threats and appropriate responses to stimuli. However, the challenge is to enable flexible electronics to respond to mechanical stimuli such as biological skin, and researchers have not clearly reported the successful integration of somatic mechanical perception and sensation management functions into neuro-like electronics. In this work, an afferent nerve-like device with a pressure sensor and a perception management module is proposed. The pressure sensor comprises two conductive fabric layers and an ionic hydrogel, forming a capacitor structure that emulates the swift transition from tactile to pain perception under mechanical stimulation. Drawing inspiration from the neuronal \"gate control\" mechanism, the sensation management module adjusts signals in response to rubbing, accelerating the discharge process and reducing the perception duration, thereby replicating the inhibitory effect of biological neurons on pain following tactile interference. This integrated device, encompassing somatic mechanical perception and sensation management, holds promise for applications in soft robotics, prosthetics, and human-machine interaction.

Sensory feedback provides critical interactive information for the effective use of hand prostheses. Non-invasive neural interfaces allow convenient access to the sensory system, but they communicate a limited amount of sensory information. This study examined a novel approach that leverages a direct and natural sensory afferent pathway, and enables an evoked tactile sensation (ETS) of multiple digits in the projected finger map (PFM) of participants with forearm amputation non-invasively. A bidirectional prosthetic interface was constructed by integrating the non-invasive ETS-based feedback system into a commercial prosthetic hand. The pressure information of five fingers was encoded linearly by the pulse width modulation range of the buzz sensation. We showed that simultaneous perception of multiple digits allowed participants with forearm amputation to identify object length and compliance by using information about contact patterns and force intensity. The ETS enhanced the grasp-and-transport performance of participants with and without prior experience of prosthetic use. The functional test of transport-and-identification further revealed improved execution in classifying object size and compliance using ETS-based feedback. Results demonstrated that the ETS is capable of communicating somatotopically compatible information to participants efficiently, and improves sensory discrimination and closed-loop prosthetic control. This non-invasive sensory interface may establish a viable way to restore sensory ability for prosthetic users who experience the phenomenon of PFM.

Multisensory integration plays a crucial role in building the sense of body ownership, i.e., the perceptual status of one\'s body for which the body is perceived as belonging to oneself. Temporal and spatial mismatching of visual and tactile signals coming from one\'s body can reduce ownership feelings towards the body and its parts, i.e., produce disownership feelings. Here, we investigated whether visuo-tactile conflict also affects the sensorimotor representation of the body in space (i.e., body schema) and the perception of the space around the body in terms of action potentiality (i.e., reaching space). In two experiments, body schema (Experiment 1) and reaching space (Experiment 2) were assessed before and after either synchronous or asynchronous visuo-tactile stimulation. Results showed that the asynchronous condition, provoking multisensory conflict, caused disownership over one\'s hand and concurrently affected the body schema and the reaching space. These findings indicate that body schema and reaching space could be dynamically shaped by the multisensory regularities that build up the sense of body ownership.

OBJECTIVE: The threshold values of two-point discrimination (TPD) provide a numerical measure of tactile acuity. Normal reference values are needed to decide whether sensory variability is within normal sensorial limits. The study aimed to determine the upper extremity and face threshold values in healthy young adults.
METHODS: Static TPD thresholds of 67 healthy young adults aged 18-35 years were assessed. Eight skin areas in the face and upper extremity on the dominant side were assessed using a \"method of limits\" approach with an aesthesiometer. Differences between genders were examined with the Mann-Whitney U test. The Spearman correlation analysis investigated the relationship between age and TPD measurements.
RESULTS: TPD values ranged between 4.66 and 19.16 mm and 1.33-68.66 mm in the face and upper extremity, respectively, in the participants with a mean age of 23.83 ± 4.66 years. Fingertips and the area over the lateral mandibula showed the greatest sensitivity. The threshold values of TPD showed both interindividual and intraindividual variability. There was no statistical difference in the TPD values according to gender in any of the measured areas, and there was no relationship between age and TPD test values.
CONCLUSIONS: The threshold values of TPD have clinical applicability in various diseases affecting the sensation of the upper extremity and/or face. These data may help the detection of early sensory loss.

Rodents use their whisker system to discriminate surface texture. Whisker-based texture discrimination tasks are often used to investigate the mechanisms encoding tactile sensation. One such task is the textured Novel Object Recognition Test (tNORT). It takes advantage of a tendency of rodents to explore novel objects more than familiar ones and assesses the sensitivity of whiskers in discriminating different textures of objects. It requires little training of the animals and the equipment involved is a simple arena with typically two objects placed inside. The success of the test relies on rodents spending sufficient time exploring these objects. Animals may lose interests in such tasks when performed repetitively within a limited time frame. However, such repeated tests may be crucial when establishing a sensitivity threshold of the whisker system. Here we present an adapted rodent tNORT protocol designed to maintain sustained interest in the objects even with repeated testing. We constructed complex objects from three simple-shaped objects. Different textures were provided by sandpapers of varying grit sizes. To minimise olfactory clues, we used the sandy and the laminar side of the same sandpaper as the familiar and novel textures assigned at random. We subsequently conducted repeated tNORTs on eight rats in order to identify a critical threshold of the sandpaper grit size below which rats would be unable to discriminate the sandy from the laminar side. With an inter-test-interval of seven days and after five tNORTs, the protocol enabled us to successfully identify the threshold. We suggest that the proposed tNORT is a useful tool for investigating the sensitivity threshold of the whisker system of rodent, and for testing the effectiveness of an intervention by comparing sensitivity threshold pre- and post-intervention.

Touch is an essential form of non-verbal communication. While language and its neural basis are widely studied, tactile communication is less well understood. We used fMRI and multivariate pattern analyses in pairs of emotionally close adults to examine the neural basis of human-to-human tactile communication. In each pair, a participant was designated either as sender or as receiver. The sender was instructed to communicate specific messages by touching only the arm of the receiver, who was inside the scanner. The receiver then identified the message based on the touch expression alone. We designed two multivariate decoder algorithms-one based on the sender\'s intent (sender-decoder), and another based on the receiver\'s response (receiver-decoder). We identified several brain areas that significantly predicted behavioural accuracy of the receiver. Regarding our a priori region of interest, the receiver\'s primary somatosensory cortex (S1), both decoders were able to accurately differentiate the messages based on neural activity patterns here. The receiver-decoder, which relied on the receivers\' interpretations of the touch expressions, outperformed the sender-decoder, which relied on the sender\'s intent. Our results identified a network of brain areas involved in human-to-human tactile communication and supported the notion of non-sensory factors being represented in S1. This article is part of the theme issue \'Sensing and feeling: an integrative approach to sensory processing and emotional experience\'.

We present novel research on the cortical dynamics of atypical perceptual and emotional processing in people with symptoms of depersonalization-derealization disorder (DP-DR). We used electroencephalography (EEG)/event-related potentials (ERPs) to delineate the early perceptual mechanisms underlying emotional face recognition and mirror touch in adults with low and high levels of DP-DR symptoms (low-DP and high-DP groups). Face-sensitive visual N170 showed markedly less differentiation for emotional versus neutral face-voice stimuli in the high- than in the low-DP group. This effect was related to self-reported bodily symptoms like disembodiment. Emotional face-voice primes altered mirror touch at somatosensory cortical components P45 and P100 differently in the two groups. In the high-DP group, mirror touch occurred only when seeing touch after being confronted with angry face-voice primes. Mirror touch in the low-DP group, however, was unaffected by preceding emotions. Modulation of mirror touch following angry others was related to symptoms of self-other confusion. Results suggest that others\' negative emotions affect somatosensory processes in those with an altered sense of bodily self. Our findings are in line with the idea that disconnecting from one\'s body and self (core symptom of DP-DR) may be a defence mechanism to protect from the threat of negative feelings, which may be exacerbated through self-other confusion. This article is part of the theme issue \'Sensing and feeling: an integrative approach to sensory processing and emotional experience\'.