Event-Related Potentials to Known and Unknown Words in 18 and 24 Month Olds At Risk for ASD

Background:  In typical development, the brain’s event-related potentials (ERPs) to words becomes increasingly localized and lateralized within the left hemisphere as infants become more proficient with language (Mills et al., 2005).  Here, we investigated this developmental process in toddlers who are at a high risk (HRA) for developing autism spectrum disorders (ASD) due to having an older sibling with an ASD.   Converging research suggests that individuals with ASD may show atypical neural response to linguistic stimuli in addition to displaying reversed or dampened lateralization of language networks in the brain.  However, it is unclear how early in development these atypicalities are present and whether they are linked specifically to autism symptoms or to more general language impairment.  Importantly, while approximately 10 to 20% of HRA toddlers will develop an ASD, a large proportion of those who do not ultimately receive a clinical diagnosis will experience language delay/impairment or subclinical traits of a broader ASD endophenotype.  Therefore, this high risk population will allow us to begin to tease apart the effects of language impairment and ASD symptoms on neural response to words and language.

Objectives: To examine whether HRA infants show atypical electrophysiological response to words, and if so whether this is more closely linked to language delay, autism symptoms, or both.

Methods:  As part of a larger longitudinal study, we recorded ERPs to words in HRA infants and low-risk control (LRC) infants at 18 (HRA n=26; LRC n=25) and 24 months (HRA n=28; LRC n=18).  Participants listened to a stream of words, half of which were known to the infant (confirmed with parent report) and half of which were unknown.  The Mullen Scales of Early Learning (MSEL) and Autism Diagnostic Observation Schedule (ADOS) were administered at both ages in order to obtain indices of language ability and autism symptoms. 

Results:  Grand averaged waveforms revealed a negative inflection maximal over posterior electrodes (N200).  A preliminary analysis from a subset of 17 HRA and 10 LRC infants at 18 months indicated that this N200 was larger to known than unknown words in LRC infants over the left parietal region (p=.002).  In contrast, this difference was not significant in HRA infants, although they did show a trend in the same direction (p=.095).  Planned analyses will examine this component in infants at 24 months and will explore the relationship between N200, language ability, and autism symptoms at both ages.

Conclusions: We have preliminary evidence that HRA infants do not show the same pattern of response to words as LRC at 18 months.  This suggests that atypical processing of lexical stimuli may be a trait of the ASD endophenotype.  Our work will investigate the nature of this atypical processing with the hope of identifying whether this is driven by infants with delayed language or by infants who are displaying symptoms of ASD.