Functional Organization for Rapid Auditory Processing is Disrupted in Adult Dyslexics: An fMRI Study

Abstract:
Children and adults with certain language disorders have been shown to have a deficit in processing rapid auditory information (Tallal et al., 1974, Witton et al., 1998). We used fMRI to explore the neural bases of rapid auditory processing in adult dyslexics and controls. To identify regions involved in rapid auditory processing, we scanned subjects while they heard nonlinguistic stimuli with either rapid (50 ms) or slow (200 ms) formant transitions and high (250 Hz) or low (125 Hz) fundamental frequency. Ten blocks each of rapid and slow tones were presented (alternating every 16.6 seconds) and subjects performed a pitch judgment task. Both groups performed equally well on the pitch judgment. Comparison between brain activity associated with the perception of rapid and slow formant transitions showed greater activity for rapid transitions in the left prefrontal cortex, left putamen and right caudate. Adult dyslexics did not show activity for rapid transitions in the left prefrontal cortex or the basal ganglia. These results suggest that frontal and striatal structures make up a network involved in the processing of rapid auditory information and that network is disrupted in adult dyslexics.