Autistic Traits Associated with Diminished Response to Affective Touch

Background:

Touch enables us to navigate not only the physical, but also the social world, and plays a vital role in early development and social interactions. Recently, neuroscientists have begun to study ‘affective’ or social touch which has been linked to a class of slow-conducting, unmyelinated nerves, CT afferents, present only in the hairy skin of mammals, including humans. Microneurography studies have shown that CT-optimal stroking speeds range from 1-10 cm/s and pleasantness ratings for this slow, gentle touch follow the same pattern. Such touch is reminiscent of that seen in social interactions, and several key nodes of the ‘social brain’ have recently been found to be involved in processing such touch. Sensory issues are often present in children with Autism Spectrum Disorder (ASD) and some of the social brain regions implicated in processing affective touch are known to be disrupted in ASD. Further, some of these regions, including the posterior superior temporal sulcus (pSTS), have been shown to exhibit a varied response to visual social stimuli as a function of the observer’s autistic traits.  Notably, autistic traits are present and normally distributed in the general population.

Objectives:

We sought to examine the relationship between individual differences in autistic traits and the neural response to CT-optimal, affective touch. In addition, we investigated the relationship between autistic traits and self-reported social touch preferences.

Methods:

During an fMRI scan, nineteen healthy adults received alternating blocks of slow (CT-optimal) and fast (non-optimal) brushing to the forearm. Participant also completed the Autism-Spectrum Quotient (AQ) and the Social Touch Questionnaire (STQ).

Results:

Relative to fast touch, the slow touch activated contralateral insula, pSTS, medial prefrontal cortex (mPFC), orbitofrontal cortex (OFC), and amygdala. Connectivity analyses revealed co-activation of the mPFC, insula and amygdala during slow touch. Participants’ autistic traits negatively correlated with the response to slow touch in the OFC and pSTS. There was also a positive correlation between AQ and STQ scores, indicating that individuals with more autistic traits had less of a preference for social touch.

Conclusions:

The current study revealed that brain responses to affective touch vary as a function of individual’s autistic traits, illustrating a tight coupling of social function and social perception, beyond the visual domain, in typical adults.  Participants with more autistic traits showed a diminished response to slow, affective touch in social brain regions, raising the question of whether or not processing deficits of affective touch, processed by the CT-system, are evident in individuals with ASD.