“Nothing eases suffering like human touch.” — Bobby Fischer
The gentle caress of a mother to her child. A reassuring pat on the shoulder from a friend. The touch of another human is one of the first forms of communication we experience in life, preceding the development of spoken language. Touch can have a remarkable effect on our emotional, psychological, and physiological states. It shapes our relationships with others and helps us build social connections.
The positive effects of touch are primarily associated with affective touch, characterized by comforting, caress-like stroking that activates C-tactile afferent (CT-afferent) neurons in the skin of mammals (including humans). Affective touch has attracted the interest of researchers seeking to decode how the sympathetic nervous system confronts and manages a variety of challenges, including pain regulation, stress management, and social interactions. The subject has drawn attention in the study of neurodevelopmental disorders, such as Autism Spectrum Disorders (ASD), where it is playing an essential role in understanding the sensory and social challenges facing individuals with atypical neurocognitive function.
While studies on touch, and affective touch specifically, utilize a range of physiological signals to gather data, electrodermal activity (EDA) has proven particularly useful in this area. Also referred to as Galvanic Skin Response (GSR), EDA provides a direct window into the sympathetic nervous system, which is responsible for emotional or affect-related arousal. When someone experiences pleasant or meaningful touch (e.g., a gentle stroke or supportive hand), the brain triggers subtle changes in sweat gland activity manifested as shifts in skin conductance. These changes occur when people aren’t fully aware of their emotional response. This makes EDA a sensitive, objective marker of how the body reacts to social and tactile experiences. In studies of affective touch, researchers track EDA to see whether a touch feels calming, engaging, or stressful, and how these responses differ across individuals or clinical groups such as autistic youth. Because EDA reflects genuine physiological arousal tied to emotional processing, it helps scientists understand the underlying autonomic mechanisms that shape how we experience social touch.
Researchers at the University of Tours in France examined how children with ASD respond to gentle, affective touch to determine whether they exhibit physiological patterns that differ from those of their neurotypical peers under the same conditions. The team measured multiple aspects of the autonomic nervous system, including EDA and electrocardiogram (ECG). These signals were collected using a BIOPAC MP36 data acquisition and analysis system to capture subtle changes in sympathetic arousal. Researchers collected EDA data using two 8 mm Ag/AgCl cup electrodes placed on the second phalanges of the index and middle fingers of the right hand. ECG was collected via two disposable vinyl electrodes placed on the sternum and on the right shoulder. The study found that autistic children exhibited atypical EDA responses, showing either blunted or inconsistent autonomic reactions relative to controls, even when their outward behavior appeared typical. These results suggest that affective touch may not regulate internal arousal in autistic children the same way it does in others, providing an essential insight for therapies and sensory-based interventions that rely on touch.
In a similar study, a team from the University of Turin in Italy explored how autistic adults process affective touch by comparing their subjective ratings of pleasantness with their physiological responses. The researchers used a BIOPAC data acquisition research system with an EDA amplifier module to record EDA. At the same time, participants received gentle, slow stroking intended to activate the brain’s affective touch pathways. The goal was to determine whether autistic adults show a mismatch between what they say they feel and how their bodies respond. The findings revealed an apparent dissociation. While autistic participants often rated the touch similarly to neurotypical participants, their EDA responses differed significantly, indicating altered sympathetic arousal. This physiological-subjective mismatch provides compelling evidence that affective touch is processed differently in ASD, which may help explain challenges with social touch and sensory integration in everyday interactions.
Researchers from the University of Liverpool and Manchester Metropolitan University examined how brief, naturalistic social touch alters brain activity, autonomic physiology, and emotion recognition performance. Although this multimodal study did not focus on an autism-only sample, it is relevant to social-touch research more broadly and provides methodological examples that apply to ASD studies. To capture changes in prefrontal cortex function, the team employed a BIOPAC fNIRS imager system, with signals sent to a data acquisition unit. Further analysis of fNIRS signals was handled via fNIRS visualization software. Both EDA and photoplethysmography (PPG) were recorded at 2 kHz, using shielded Ag/AgCl electrodes on the index and fourth fingers and a PPG sensor on the middle finger, and were acquired and analyzed in AcqKnowledge. The results showed that social touch increased prefrontal activation, modulated cardiac and vascular dynamics captured via PPG, and produced measurable changes in sympathetic arousal, as indexed by EDA. Participants also demonstrated improved emotion-recognition accuracy following touch. Together, these findings suggest that social touch engages coordinated central and peripheral systems in ways that may support social cognition and emotional understanding.
These are just a few examples of how EDA is being used in research into affective touch. For additional information on integrating EDA in your study, see our multiple webinars on the subject.
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