ERP Phase Synchrony in Language Networks Is Highly Correlated with Language and Cognitive Abilities in Autistic and Typical Children

Background:  The autism spectrum disorders (ASDs) are a heterogeneous group of neurodevelopmental disorders that share a behavioral phenotype classically described as impairment of social communication accompanied by repetitive or stereotyped behaviors. Biological models supported by neuroimaging studies are converging on a biological phenotype shared by these disorders, specifically, altered functional connectivity in and among critical cortical networks. Phase synchrony is a measurement of electrocortical synchronization of oscillatory brain rhythms across neural networks, hypothesized as a mechanism for functional connectivity.  Language deficits in autism may be due in part to a failure of integration and synchronization of phonological information across critical language networks. We sought to test the hypothesis that during auditory processing of phonemes, autistics would show decreased functional connectivity between temporal and frontal language networks and that the degree of impaired connectivity would correlate with severity of language impairment.    

Objectives:  To analyze phase synchrony between activated regions in primary auditory cortex (STG) and defined frontal language networks (Broca’s area) during phonemic cortical auditory evoked potentials in age-matched autistic and typical children and compare the phase synchrony to cognitive and language abilities.  

Methods:  Auditory ERP's in response to a standard phoneme, //ge//, and a deviant, //be//, were recorded from children (ages 5 to 8 yr) with autism spectrum disorders (n = 6) and age-matched typical controls (n = 8) using high-density array nets and 128 channel EEG. Cortical activation in source space derived from the evoked response to the standard phoneme was mapped onto a standard adult whole head model (inflated cortex) for each subject and average maps of the group data were generated for the two groups: ASD and controls.   The phase synchrony between the activated auditory cortex (LSTG) and Brodmann’s area 45 (Br45) was computed for each subject. The correlation coefficients were calculated for phase synchrony and general cognitive ability (GCA) and verbal cognitive ability (VCA) as measured on the Differential Abilities Scale. 

Results:  Phase synchrony between regions of activation in LSTG and Br45 for the alpha band after Bonferroni correction was found to show a strong positive correlation with both GCA and VCA for typical and ASD subjects.   Using the Kendall Correlation (tau), phase synchrony to GCA had a correlation of  0.57 and a p value of 0.0052.  Specific correlations for other language measures will also be presented.  Non-alpha frequency bands failed to show significant correlations.  

Conclusions:  These results support the view that language impairment in children with ASD is related to impaired functional connectivity between critical language networks. Our ability to demonstrate and quantitate this impairment using EEG underscores the value of this technology for measuring functional biomarkers in behaviorally challenged young children with autism. This methodology will be applied to at risk infants to identify functional language impairment before behavioral correlates are clinically apparent.  This technique has the potential to show the failure of the at risk brain to develop compensatory mechanisms during ontogeny and thus could provide an indication for interventions to improve the functional outcome.