Induced Microgyria and Auditory Temporal Processing in Rats: A Model for Language Impairment?

Studies have shown the existence of minor developmental corticalmalformations, including microgyria, in the brains of dyslexics.Concomitant studies have shown that language-impaired individualsexhibit severe deficits in the discrimination of rapidly presentedauditory stimuli, including phonological and nonverbal stimuli(i.e., sequential tones). In an effort to relate these results,male rats with neonatally induced microgyria were tested inan operant paradigm for auditory discrimination of stimuli consistingof two sequential tones. Subjects were shaped to perform a go/no-gotarget identification, using water reinforcement. Stimuli werereduced in duration from 540 to 249 msec across 24 d of testing.Results showed that all subjects were able to discriminate atlonger stimulus durations. However, bilaterally lesioned subjectsshowed specific impairment at stimulus durations of 332 msecor less, and were significantly depressed in comparison to shams.Right- and left-lesioned subjects were significantly depressedin comparison to shams at the shortest duration (249 msec).These results suggest a possible link between the neuropathologicanomalies and the auditory temporal processing deficits reportedfor language-impaired individuals.