Induced microgyria and auditory temporal processing in rats: a model for language impairment?

Studies have shown the existence of minor developmental cortical malformations, including microgyria, in the brains of dyslexics. Concomitant studies have shown that language-impaired individuals exhibit severe deficits in the discrimination of rapidly presented auditory 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 in an operant paradigm for auditory discrimination of stimuli consisting of two sequential tones. Subjects were shaped to perform a go/no-go target identification, using water reinforcement. Stimuli were reduced in duration from 540 to 249 msec across 24 d of testing. Results showed that all subjects were able to discriminate at longer stimulus durations. However, bilaterally lesioned subjects showed specific impairment at stimulus durations of 332 msec or less, and were significantly depressed in comparison to shams. Right- and left-lesioned subjects were significantly depressed in comparison to shams at the shortest duration (249 msec). These results suggest a possible link between the neuropathologic anomalies and the auditory temporal processing deficits reported for language-impaired individuals.