Brain Responses to Temporally Novel Sound in Children with Autism: Evidence for Reduced Involvement of the Right Hemisphere

Background:
Unresponsiveness to sound is commonly observed in autism and may relate to a reduced capacity for attention orienting.

Objectives:
The present study was aimed at determining whether young children with autism display abnormalities at early stages of automatic allocation of attention to temporally novel sound presented in nonattended channel.

Methods:
Subjects were twenty one 3-8 year old children with autism and twenty one age-matched typically developing children. While watching a silent movie, subjects were presented with pairs of clicks separated by a 0.5 s intra-pair interval, with longer (7-9 s) intervals between pairs. We assess electroencephalographic (EEG) perturbations and event-related potentials (ERP) in response to sounds of different temporal novelty (first and second click in the pair).

Results:
In control children, the early attention-modulated midtemporal N1c wave of EPR and corresponding EEG phase locking and power increase in response to the first click were right-lateralized and were bilaterally higher than in response to the second click. Children with autism demonstrated abnormal first click responses, characterized by reduced N1c amplitude and EEG phase locking in the right midtemporal region, reversed leftward lateralization of the EEG phase locking and absence of the later frontal N2 wave. Their brain responses to the second click were essentially normal. The behavioral and heart rate analysis suggested that the two groups did not differ in respect to baseline arousal or preliminary (in)attention to the click stimuli. Therefore, the between-group differences in response to the first click could be explained by differences in initial orienting response to temporally novel events.

Conclusions:
The impaired right hemispheric processing of temporary and contextually novel information and suboptimal hemispheric lateralization of normally right-lateralized orienting and alerting networks may importantly contribute to development of the social deficits in young children with autism.