Children with autism show reduced somatosensory response: an MEG study

Abstract

The neural underpinnings of sensory processing differences in autism remain poorly understood. This prospective magnetoencephalography (MEG) study investigates whether children with autism show atypical cortical activity in the primary somatosensory cortex (S1) in comparison with matched controls. Tactile stimuli were clearly detectable, and painless taps were applied to the distal phalanx of the second (D2) and third (D3) fingers of the right and left hands. Three tactile paradigms were administered: an oddball paradigm (standard taps to D3 at an interstimulus interval (ISI) of 0.33 and deviant taps to D2 with ISI ranging from 1.32 s to 1.64 s); a slow-rate paradigm (D2) with an ISI matching the deviant taps in the oddball paradigm; and a fast-rate paradigm (D2) with an ISI matching the standard taps in the oddball. Study subjects were boys (age 7-11 years) with and without autism disorder. Sensory behavior was quantified using the Sensory Profile questionnaire. Boys with autism exhibited smaller amplitude left hemisphere S1 response to slow and deviant stimuli during the right-hand paradigms. In post-hoc analysis, tactile behavior directly correlated with the amplitude of cortical response. Consequently, the children were re-categorized by degree of parent-report tactile sensitivity. This regrouping created a more robust distinction between the groups with amplitude diminution in the left and right hemispheres and latency prolongation in the right hemisphere in the deviant and slow-rate paradigms for the affected children. This study suggests that children with autism have early differences in somatosensory processing, which likely influence later stages of cortical activity from integration to motor response.

Figure 1. Somatosensory Magnetoencephalography Paradigms

Three tactile paradigms are presented to the right and left hands. Note: Paradigm 1: Five hundred standard taps delivered to middle finger (D3), with 100 deviant taps to index finger (D2) pseudo-randomly interspersed between every three to seven standard taps; Paradigm 2: 100 taps delivered to D2 (the deviant finger) at the same rate as the deviant in the oddball paradigm; Paradigm 3: 100 taps delivered to D2 at the same rate as the standard in the oddball paradigm.

Figure 2. Somatosensory evoked field (SEF) raw data and group averaged amplitude data

A. Example of a typical SEF data from the left hemisphere slow-rate paradigm response measures in participant, HC7. B. Group averaged amplitude data from the autism cohort and control cohort derived from the left hemisphere responses to the slow-rate condition. Note: RMS=root mean square in femtotesla (fT); ms=millisecond; HC=healthy control; AD=autism disorder.

Figure 3. Box Plots of Somatosensory Cortical Amplitudes in response to Tactile Stimulation

a. Top row depicts the left and right hemisphere amplitudes in femtotesla (fT) for the children with and without autism. B. Bottom row depicts the left and right hemisphere amplitudes for the children with and without tactile sensitivity. Note: On these Matlab generated box plots, the horizontal lines denote group median values, whiskers represent 1.5 times the interquartile range, and + indicates outlier values beyond the whiskers.

Figure 4. Correlation of Tactile Sensory Profile Score and Somatosensory Evoked Field Amplitude

This scatter graph includes Tactile Sensory Profile (TSP) scores from all participants relative to their left hemisphere amplitude response to the slow stimuli.