Abstract
Atypical language is a fundamental feature of autism spectrum conditions (ASC), but few studies have examined the structural integrity of the arcuate fasciculus, the major white matter tract connecting frontal and temporal language regions, which is usually implicated as the main transfer route used in processing linguistic information by the brain. Abnormalities in the arcuate have been reported in young children with ASC, mostly in low-functioning or non-verbal individuals, but little is known regarding the structural properties of the arcuate in adults with ASC or, in particular, in individuals with ASC who have intact language, such as those with high-functioning autism or Asperger syndrome. We used probabilistic tractography of diffusion-weighted imaging to isolate and scrutinize the arcuate in a mixed-gender sample of 18 high-functioning adults with ASC (17 Asperger syndrome) and 14 age- and IQ-matched typically developing controls. Arcuate volume was significantly reduced bilaterally with clearest differences in the right hemisphere. This finding remained significant in an analysis of all male participants alone. Volumetric reduction in the arcuate was significantly correlated with the severity of autistic symptoms as measured by the Autism-Spectrum Quotient. These data reveal that structural differences are present even in high-functioning adults with ASC, who presented with no clinically manifest language deficits and had no reported developmental language delay. Arcuate structural integrity may be useful as an index of ASC severity and thus as a predictor and biomarker for ASC. Implications for future research are discussed.
Highlights
Communication impairments are archetypal of Autism spectrum conditions (ASC), with delayed or absent language development the primary cause of concern and referral in many cases (Siegel et al, 1988; De Giacomo and Fombonne, 1998)
We aimed to investigate the structural integrity of the arcuate fasciculus in a homogenous group of highfunctioning adults with ASC who did not show any intellectual disability or obvious language impairments
Probabilistic tractography revealed a significant volumetric reduction of the arcuate fasciculus, an effect strongest in the right hemisphere, in high-functioning individuals with ASC as compared with typical controls. This result could in part be attributed to group differences in intracranial volume (ICV), multiple regression of ICV did not appear to contribute significantly to right arcuate volume and, crucially, analysis of male participants only confirmed these volumetric differences in groups matched for ICV
Summary
Communication impairments are archetypal of ASC, with delayed or absent language development the primary cause of concern and referral in many cases (Siegel et al, 1988; De Giacomo and Fombonne, 1998). The diagnosis of Asperger syndrome (DSM IV-TR: American Psychiatric Association, 2000), one of the major variants of ASC, was previously given on the basis of typical, non-delayed language development, these individuals may show receptive and expressive language skills at “well below chronological age level” (Howlin, 2003) They are noted for their use of idiosyncratic, pedantic language, which Hans Asperger described in his “little professor” patients (Asperger, 1944). This particular feature may be the linguistic expression of difficulties with ‘theory of mind’ (inaccurately assessing the knowledge of their listeners), and ‘weak central coherence’ (providing irrelevant and uninformative detail rather than summarizing the ‘gist’ of the matter). The neuronal basis of language difficulties in ASC, which seem to affect all linguistic levels (phonological, lexical, syntactic, semantic, and pragmatic), requires further study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
