Disrupted Neural Response to Affective Touch in ASD

Background: Social, or affective, touch plays a critical role in early development and interpersonal interactions throughout the lifespan. A special class of nerve fibers, C-tactile afferents, which are present only in hairy skin, has been found to respond to such slow, gentle touch. We recently identified a network of brain regions involved in processing affective touch targeting C-tactile afferents in typical adults, including the posterior superior temporal sulcus (pSTS) and insular cortex. These key nodes of the ‘social brain’ have been shown to be disrupted in Autism Spectrum Disorder (ASD) in a variety of social perception paradigms. This is the first neuroimaging study to examine tactile social perception in ASD. Given the importance of touch in early socio-emotional development, and known sensory issues inASD, it is important to examine brain mechanism for processing affective touch in individuals with this neurodevelopmental disorder.

Objectives: Using functional magnetic resonance imaging (fMRI), we sought to characterize the brain mechanisms for processing C-tactile targeted affective touch in typically developing (TD) children and those with ASD.

Methods: Thirty-eight children with and without ASD (matched on age and IQ) participated in the study. During a 10-minute fMRI scan, participants received continuous brushing to the Arm or Palm in a block design procedure. There were 2 runs of each condition, including 8 repetitions of 6-second blocks of touch followed by 12 seconds of rest (no touch). Tactile stimuli were slow strokes (8cm/s) with a 7cm wide brush administered by a trained experimenter.

Results: We implemented a region of interest (ROI) analysis, using bilateral insula and right pSTS ROIs. First, we examined the differential response to Arm (CT-targeted) and Palm (non-CT) touch in three bilateral insula regions. The groups showed a significantly different response to Arm vs. Palm touch in the dorsal anterior insula. Unlike those with ASD, TD children showed a greater response to the Arm relative to Palm in this region. The groups did not differ in their posterior or ventral anterior insular responses. In the right pSTS, there was a trend toward a group difference in the response to Arm vs. Palm touch.

Conclusions: The current fMRI study indicates that children with ASD have disrupted neural mechanisms for processing affective touch (targeting C-tactile afferents). Notably, TD and ASD groups revealed comparable activity in response to gentle touch in the posterior insula, a region involved in processing primary sensory input. However, the groups differed in the dorsal anterior insular response. This region has been shown to be important for interpreting affective aspects of somatosensory/interoceptive information, influencing decision-making and behavior. Similarly, children with ASD exhibited a dampened response to affective touch in the pSTS, a region involved in a variety of social perception tasks, including the visual perception of biological motion. These findings raise questions regarding the developmental trajectory of disrupted brain mechanisms for processing affective touch. We will discuss implications of our results for early diagnosis and intervention.