Brainstem timing deficits in children with learning impairment may result from corticofugal origins

A substantial proportion of children with language-based learning problems [learning disabilities (LD)] display abnormal encoding of speech at rostral levels of the auditory brainstem (i.e. midbrain) as measured by the auditory brainstem response (ABR). Of interest here is whether these timing deficits originate at the rostral brainstem or whether they reflect deficient sensory encoding at lower levels of the auditory pathway. We describe the early brainstem response to speech (waves I and III) in typically developing 8- to 12-year-old children and children with LD. We then focus on the early brainstem responses in children with LD found to show abnormal components of the rostral speech-evoked ABR (waves V and A). We found that wave I was not reliably evoked using our speech stimulus and recording parameters in either typically developing children or those with LD. Wave III was reliably evoked in the large majority of subjects in both groups and its timing did not differ between them. These data are consistent with the view that the auditory deficits in the majority of LD children with abnormal speech-evoked ABR originate from corticofugal modulation of subcortical activity.