Phonological processing in first-degree relatives of individuals with autism: an fMRI study

Autism spectrum disorders (ASD) are complex neurodevelopmental disorders. Twin studies have provided heritability estimates as high as 90% for idiopathic ASD. Further evidence for the spectrum's heritability is provided by the presence of the broad autism phenotype (BAP) in unaffected first-degree relatives. Language ability, specifically phonological processing, is proposed to be a core BAP trait. To date, however, no functional neuroimaging investigations of phonological processing in relatives of individuals with ASD have been undertaken. We conducted a functional magnetic resonance imaging (fMRI) study in parents of children with ASD utilizing a priming task probing implicit phonological processing. In our condition that placed heavier demands on phonological recoding, parents exhibited greater hemodynamic responses than controls in a network of cortical regions involved in phonological processing. Across conditions, parents exhibited enhanced priming-induced response suppression suggesting compensatory neural processing. A nonword repetition test used in previous studies of relatives was also administered. Correlations between this measure and our functional measures also suggested compensatory processing in parents. Regions exhibiting atypical responses in parents included regions previously implicated in the spectrum's language impairments and found to exhibit structural abnormalities in a parent study. These results suggest a possible neurobiological substrate of the phonological deficits proposed to be a core BAP trait. However, these results should be considered preliminary. No previous fMRI study has investigated phonological processing in ASD, so replication is required. Furthermore, interpretation of our fMRI results is limited by the fact that the parent group failed to exhibit behavioral evidence of phonological impairments.