Auditory Evoked Potentials: Candidate Endophenotypic Indices of ASD Susceptibility

Background: Autism spectrum disorders (ASD) are characterized by early-emerging social and communication impairments.  Abnormal auditory sensory processing as well as atypical preferences to computerized non-speech sounds over human speech has been reported in ASD children. The latter deficit might be rooted in atypically persistent sensitivity to non-native speech or non-human sounds, which normally declines between 6 and 12 months in typically developing infants (TD).

Objectives: The purpose of the current study was to examine the time-course of brain activity at preattentive stages for both native (English) and non-native (Hindi) speech sounds in a design that allowed exploration of familial aggregation of electrophysiologic traits.

Methods: Fourteen males with ASD, 17 unaffected siblings (US) and 12 TD controls (age 15-22, mean 18 for all groups) participated in an electrophysiological (EEG) study and performed a speech-sound version of a Mismatch Negativity (MMN) paradigm incorporating native (English) and non-native (Hindi) speech sounds.

Results: Contrary to our expectation, there were no differences between the groups in the MMN component of the ERP, indicating intact automatic change detection in ASD subjects.  However, earlier sensory components (P1 and N1), were abnormal in ASD subjects, and these abnormalities were correlated with severity of ASD, as assessed by the Social Responsiveness Scale. Crucially, these enhanced P1 and delayed N1 responses in ASD subjects were specific to non-native speech sounds and not observed in response to native speech. The enhanced P1 amplitude in the non-native condition was also observed in unaffected siblings (US), suggesting a familial risk effect for ASD. Noteworthy, the P1 amplitude was significantly smaller for non-native compared to native sounds in TD and US, but not in ASD group, suggesting the lack of difference between conditions as a disease-state effect.

Conclusions: Our study provided evidence for abnormal early stage processing of non-native sounds in ASD and US groups. Enhanced amplitude of the early sensory component P1 warrants further exploration as an intermediate phenotype (endophenotype) for ASD.