A MEG Investigation of Phonological Processing in Autism

Background: Deficits involving phonology, one of six proposed core broad autism traits, are observed in a large subset of children with autism and have been reported in two samples of proband parents.  Despite this, no neuroimaging studies have investigated phonological processing in individuals with autism or their first-degree relatives.

Objectives: Magnetoencephalography (MEG) was utilized to investigate the neurobiology of phonological processing in adults with autism as well as parents of individuals with autism.  The aim of the present study was to examine the presence of phonological processing deficits in individuals with autism as well as unaffected first-degree relatives in order to provide evidence in favor of or against the inclusion of phonological processing deficits as a core trait of the broad autism phenotype (BAP).

Methods: Sixteen parents of a child with autism, thirteen adults with autism and seventeen controls performed a phonological priming task while undergoing whole-cortex MEG.  The task consisted of four prime-target word conditions including homophones (e.g., PAUSE-paws) and related stimuli.  Primes were presented below perceptual threshold (i.e., 30ms).  Subjects, who were not informed that stimuli consisted of word pairs, performed a lexical decision task (i.e., is it a word or a nonword?) on all lowercase targets.

Results: In our priming condition that placed heavier demands on phonological decoding skills, adults with autism exhibited reduced evoked gamma band activity relative to both parents and controls in the left supramarginal gyrus (SMG).  Reductions in evoked gamma activity were also observed in adults with autism for unprimed relative to primed stimuli in the left SMG relative to the control group and in the right SMG relative to the parent group.  Furthermore for unprimed relative to primed stimuli, reductions in induced gamma activity were observed in adults with autism relative to the parent group in the left inferior frontal gyrus.  No differences in evoked or induced gamma activity were observed between the parent and control groups.

Conclusions: These results are consistent with phonological processing deficits in individuals with autism.  However, the present results do not strongly implicate phonological deficits in the parent group.  While greater frontal activity in the parent group may be indicative of compensatory processes, our results suggest that phonological processing deficits are not a core component of the BAP.