Objectives: We sought to localize brain sources of the abnormal reaction to clicks in ASD using MEG. We also tested the hypothesis that these auditory processing abnormalities correlate with severity of autism or contribute to sensory difficulties observed in the majority of ASD individuals.
Methods: MEG and structural MRIs were obtained in 14 ASD children aged 8-13 years and 15 age-matched TDC. Presence of sensory abnormalities was assessed with Sensory Profile. Parents also answered questionnaire concerning autism symptoms during the first years of life, including sensory behavioral abnormalities. Children watched a movie while passively listening to clicks presented either binaurally or monaurally in pairs, with 1 sec ISI within a pair and 8-10 sec ISIs between the pairs. We applied distributed source modeling using minimal norm estimate (MNE) and defined regions of interest (ROIs) in the vicinity of the auditory cortex where significant activation was observed in a majority of subjects. MNE current timecourses in the ROIs were analyzed.
Results: In both groups the most prominent component of the auditory field response was P100m at approx. 100 ms. The amplitude of P100m was significantly higher in response to binaural, then monaural clicks and only in response to binaural clicks the P100m was detected in all subjects. Therefore, only binaural responses were analyzed. P100m strongly decreased upon stimulus repetition in both groups. In control subjects the P100m was right-lateralized, while no lateralization was evident in ASD children, who had tendency (p=0.06) for P100m reduction in the right hemisphere. After correction for IQ, the RH reduction of P100m correlated with greater severity of autism, assessed by child version of the Autism Quotient. Moreover, greater leftward lateralization of P100m in ASD was associated with greater severity of sensory abnormalities assessed by Sensory Profile, as well as with severely abnormal auditory behavior during the 1st year of life.
Conclusions: The P100m is thought to originate from thalamo-cortical input to infragranular cortical layers (Eggermont&Ponton, Acta Otolaryngol 2003; 123:249–52). Its reduction in the RH in ASD children suggests disturbance of RH thalamo-cortical afferents or their cortical targets that in turn may contribute to abnormal arousal and attention orienting in ASD. The correlation between sensory abnormalities and atypical leftward P100m suggests that a shift of activation balance to the left hemisphere ‘non-optimal’ for the initial orienting, may contribute to bizarre sensory behaviors in ASD.
See more of: Brain Imaging: fMRI-Social Cognition and Emotion Perception
See more of: Brain Structure & Function