Specific language impairment: Neurophysiological studies of children and their parents

Sammanfattning: Specific language impairment (SLI) is commonly described as a condition where a child with otherwise normal development and hearing does not acquire language as expected. Children with SLI often have a family history of language disorders. The aetiology is poorly understood. In the first two studies, event-related brain potentials(ERPs)evoked in response to tone- and to speech stimuli were recorded in a group of children with SLI and in their parents in order to study the electrophysiological correlates to speech and language processing in the central nervous system. The main findings were that the children with SLI and their parents showed signs of deficient late stage auditory perceptual processing as indexed by a significant longer P3 latency compared to controls in tasks requiring a phonological discrimination, whereas the earlier sensory stages as indexed by the N1 component were no different from the controls. The longer P3 latency in the parental group was associated with a positive history of language delay. It was proposed that the longer P3 latency may represent a constitutional trait contributing to the language acquisition difficulties in SLI. In the third study,ERPs in response to a visual semantic priming task were recorded in the same parental group. Despite equal performance, larger N400 amplitudes indicated that the parents, especially the fathers, were less primed by the preceding context compared to controls. Difference waveforms showed that the fathers of children with SLI, contrary to controls, had less differentiated responses to congruent versus incongruent sentence endings. It was proposed that the N400 observations may be residual markers of past language deficiencies in the fathers. In the fourth study, the regional cerebral blood flow (rCBF) distributions in children with SLI and in children with attention deficit hyperactivity disorder (ADHD) were compared using single photon emission computed tomography (SPECT). Children with SLI showed significantly lower rCBF values in the right parietal region and in the subcortical region compared to the ADHD group. The findings lend support to earlier studies suggesting deviant hemispheric lateralization as one of many factors in the aetiology of SLI, and also indicate that subcortical structures might play a role in language impairment in childhood.