Cortical auditory processing and communication in children with autism: electrophysiological/behavioral relations

Abstract

The purpose of the present study was to investigate the relations between late auditory evoked potentials (AEPs) recorded at temporal sites (the N1c wave or Tb) and verbal and non-verbal abilities in children with autism. The study was performed in 26 mentally retarded children with autism (AUT) aged 4–8 years (mean age±S.E.M.=71±2 months; mean verbal and non-verbal developmental quotient±S.E.M.=36±4 and 48±3). The stimuli used were 750 Hz tone bursts of 200 ms duration delivered binaurally at different intensity levels (50, 60, 70, 80 dB SPL) with 3–5 s interstimulus intervals. Temporal AEPs were first compared to those of a group of 16 normal children (NOR) in the same age range (mean age±S.E.M.=69±3 months). We then focused on the AUT group and considered relations between temporal AEPs and the severity of disorders of verbal and non-verbal communication assessed using a behavior rating scale. AEPs recorded on left and right temporal sites were of smaller amplitude in the AUT group than in the NOR group. Increasing intensity-related amplitude was observed on both sides in NOR and only on the right side in AUT. The lack of intensity effect on the left side resulted in a particular pattern of asymmetry at the highest level of intensity (80 dB SPL) with greater N1c amplitude on the right than on the left side (the reverse was found in the NOR group). Electro-clinical correlations indicated that the greater the amplitude of the right temporal N1c responses, the higher the verbal and non-verbal communication abilities. This suggests a developmental reorganization of left-right hemisphere functions in autism, with preferential activation of the right hemisphere for functions usually allocated to the left hemisphere, particularly those involving the secondary auditory areas situated on the lateral surface of the superior temporal gyrus where the N1c/Tb wave is generated.