Because poor comprehension has been associated with small cerebral volume and there is a high comorbidity between developmental dyslexia, attention-deficit hyperactivity disorder (ADHD), and specific language impairment, the goal of this study was to determine whether cerebral volume is reduced in dyslexia and attention-deficit hyperactivity disorder in general, as some suggest, or whether the reduction in volume corresponds to poor receptive language functioning, regardless of the diagnosis. Participants included 46 children with and without dyslexia and attention-deficit hyperactivity disorder, aged 8 to 12 years. Our results indicated that cerebral volume was comparable between those with and without dyslexia and attention-deficit hyperactivity disorder overall. However, when groups were further divided into those with and without receptive language difficulties, children with poor receptive language had smaller volumes bilaterally as hypothesized. Nonetheless, the relationship between cerebral volume and receptive language was not linear; rather, our results suggest that small volume is associated with poor receptive language only in those with the smallest volumes in both dyslexia and attention-deficit hyperactivity disorder.
Kibby, Michelle Y., Pavawalla, Shital P., Fancher, Jill B., Naillon, Angela J. and Hynd, George W. "The relationship between cerebral hemisphere volume and receptive language functioning in dyslexia and attention-deficit hyperactivity disorder (ADHD).." Journal of child neurology 24, No. 4 (Apr 2009): 438-448. doi:10.1177/0883073808324772.