Cerebral disconnection in multiple sclerosis. Relationship to atrophy of the corpus callosum.

Left ear suppression to dichotically presented verbal stimuli has been observed in patients with multiple sclerosis (MS). Rubens and coworkers have suggested that a disconnection of the auditory callosal pathways may account for this finding. To examine this proposal, we compared the performance of 28 MS patients with significant corpus callosum atrophy (CCA) on midsagittal magnetic resonance scans, 16 MS patients without significant CCA, and 64 demographically matched normal control subjects on two laterality tasks: verbal dichotic listening (consonant-vowel syllables) and tachistiscopic object-naming latency. Results indicated that left ear suppression was found only in the MS patients with CCA. Likewise, patients in the MS group with CCA were slow in responding to stimuli presented in the left visual field; this effect was not observed in patients without CCA. These findings support the hypothesis that efficiency of cross-callosal information flow is reduced in MS patients with CCA.