Neurophysiological indices of language impairment in children.
Recent investigations of children with specific language impairment (SLI) have found deviant anatomical asymmetry of the perisylvian cortex. These studies argue that this deviant anatomical asymmetry is linked to the language disorders of SLI children. To date no studies have examined whether deviant functional asymmetry underlies the processing of spoken language in these children. In the current study, brain-electrical activity was recorded from 31 scalp sites while children with SLI listened to auditorally presented stories and two different nonsense contexts. Electrical activity was time-locked to the grammatical word "the" in these contexts. The SLI children showed reversed asymmetry compared to control children from 200 ms to 400 ms in processing "the" in all contexts. More specifically, they showed depressed processing at the left temporal scalp site (T7) and enhanced processing at the right temporal site (T8). The second spatial derivative (the Laplacian) of the voltage activity was calculated to remove constant voltage potential and uniform changes in voltage potential across the scalp. The Laplacian analysis indicated that the sources of the positive electrical activity seen at the temporal electrode sites T7 and T8 are the lateral surfaces of the temporal cortices. A comparison of the scalp topography of the voltage potentials and Laplacian also suggests that children with SLI lack some contribution from a deep neural generator, possibly in the hippocampus or basal ganglia. This investigation is the first to demonstrate a direct link between deviant neurophysiological asymmetry and the processing of spoken language in children with SLI.