Normal Evoked Response to Rapid Sequences of Tactile Pulses in Autism Spectrum Disorders

Santosh Ganesan,Sheraz Khan,Keri-Lee A Garel,Matti S Hämäläinen,Tal Kenet

doi:10.3389/fnhum.2016.00433

Abstract

Autism spectrum disorder (ASD) is a developmental disorder diagnosed behaviorally, with many documented neurophysiological abnormalities in cortical response properties. While abnormal sensory processing is not considered core to the disorder, most ASD individuals report sensory processing abnormalities. Yet, the neurophysiological correlates of these abnormalities have not been fully mapped. In the auditory domain, studies have shown that cortical responses in the early auditory cortex in ASD are abnormal in multiple ways. In particular, it has been shown that individuals with ASD have abnormal cortical auditory evoked responses to rapid, but not slow, sequences of tones. In parallel, there is substantial evidence of somatosensory processing abnormalities in ASD, including in the temporal domain. Here, we tested the somatosensory domain in ASD for abnormalities in rapid processing of tactile pulses, to determine whether abnormalities there parallel those observed in the auditory domain. Specifically, we tested the somatosensory cortex response to a sequence of two tactile pulses with different (short and long) temporal separation. We analyzed the responses in cortical space, in primary somatosensory cortex. As expected, we found no group difference in the evoked response to pulses with long (700 ms) temporal separation. Contrary to findings in the auditory domain, we also found no group differences in the evoked responses to the sequence with a short (200 ms) temporal separation. These results suggest that rapid temporal processing deficits in ASD are not generalized across multiple sensory domains, and are unlikely to underlie the behavioral somatosensory abnormalities observed in ASD.

Highlights

Autism spectrum disorder (ASD) is diagnosed behaviorally, with core abnormalities in the social interactions, communication, and repetitive behavior domains
Grouping by touch score rather than by diagnosis did not result in any significant group differences. We found that both the amplitude and latencies of the evoked response to rapid sequences of tactile pulses were normal in ASD
The finding was contrary to our initial hypothesis, that rapid sensory processing deficits are prevalent in ASD across different sensory domains

Summary

INTRODUCTION

Autism spectrum disorder (ASD) is diagnosed behaviorally, with core abnormalities in the social interactions, communication, and repetitive behavior domains. Since the processing of speech sounds requires very rapid analysis of incoming sounds often separated by no more than a few milliseconds, abnormally slow processing in the auditory domain would result in behavioral deficits with the processing of speech sounds, and language. While this idea has been explored primarily in language impaired populations, it has been explored in ASD. Given the mixed findings in the field, showing increased, reduced, or normal cortical responses to somatosensory stimuli in ASD, we sought to investigate and further elucidate whether a deficit in rapid temporal processing might underlie some of the somatosensory processing abnormalities observed in ASD. We hypothesized that on this faster time interval than previously measured (Marco et al, 2012), like in the auditory domain (Oram Cardy et al, 2005), the ASD groups will be characterized by reduced responses to the second of the two pulses in the rapid sequence, but not in the slow sequence

Participants

RESULTS

DISCUSSION