In this study, we examined LH—RH anterior—posterior positional M100 asymmetry in healthy adults, children with typical development, and children with autism, and also the relationship between asymmetry and language abilities in children. Unlike children with typical development and adults, children with autism did not show evidence of the anterior—posterior M100 asymmetry previously reported in healthy adults [11
] (), supporting our hypothesis. Rather, there was no consistent pattern of relationships between LH and RH M100 source, suggesting a heterogeneous pattern of asymmetry (or lack thereof) in autism. Lack of overall asymmetry is consistent with findings of volume asymmetry abnormalities of language structures in autism. These include atypical volume asymmetry of planum temporale (one source of the M100 [11
]) and other language structures [3
We suggest that the heterogeneity of this finding may be linked with the heterogeneity of language functioning in autism. Specifically, it may be that asymmetries in autism are specifically linked with language functioning rather than a diagnosis on the autism spectrum. This suggestion is consistent with a number of previously reported findings. For example, De Fossé et al
] report reversal of volume asymmetry of Broca’s area in boys with language impairment compared with those without language impairment, irrespective of the presence of an autism diagnosis. Neural rapid temporal processing deficits have also been reported in children with language impairment and children on the autism spectrum with language impairment, but not in those whose language was unimpaired [19
], suggesting that it may be specifically language abilities that are tied to neurological signs of auditory dysfunction in autism and perhaps other disorders. Oram Cardy et al
] further report that M50 and M100 latencies, particularly in the RH, are more closely linked with language functioning than with an autism diagnosis.
This pattern of findings led us to examine the relationship between language functioning and our measure of M100 source asymmetry. We included the children with typical development because of previously reported associations of anatomical risk factors in language disorders and reading skills in normal children [21
]. An association between language abilities (measured by the CELF-4) and M100 asymmetry in the combined group with typical development and children with autism was observed (). Visual inspection of the scatterplot indicates that this relationship is evident in the comparison children alone, ruling out the possibility that the association was an artifact of the differences in the CELF-4 scores between the two groups of children. Although atypical M100 positional asymmetry is often considered a general risk factor for various neurobiological disorders, the present findings show an association between M100 positional asymmetry and language ability in particular.
This finding is consistent with similar associations between other measures of brain asymmetry and language ability. Leonard et al
] report that children and adults with learning disabilities and a lack of planum temporale asymmetry had language comprehension deficits similar to those found in SLI. Dawson et al
] used the N100 event-related potential component to derive measures of asymmetry in children with autism, dysphasia, and matched controls. Typically developing children showed stronger LH than RH responses, whereas children with autism and dysphasia showed the opposite. In children with autism, lower language scores were associated with more pronounced asymmetry reversal. Thus, strong positional asymmetry may be a sign of healthy language functioning, whereas a reduction or lack of asymmetry could indicate weaker or abnormal language functioning.
Although these findings suggest a link between language functioning and atypical asymmetry in autism, results must be treated with caution because of the small sample size and the developmental heterogeneity found among children in general and in children with autism in particular. Present findings are promising and would benefit from extension to larger groups of participants, including a group of children with SLI. SLI has been directly compared with autism (for a review, see Ref. [22
]), and SLI and autism may be phenotypically linked [3
]. As a result of the link reported here between language ability within autism and between children with and without autism, a group of children with SLI would complete the picture.