Interhemispheric transfer time differences related to aging and gender.

The difference in simple reaction times to unstructured stimuli contralateral to the hand used for response ('crossed' responses) and those stimuli ipsilateral to the hand used for response ('uncrossed' responses)--or crossed-uncrossed difference (CUD) is assumed to be a reliable index of interhemispheric transfer time (IHTT). Studies using the CUD paradigm with acallosal patients as well as a variety of populations with known variations in callosal size or functioning have demonstrated that such callosal differences are reflected in differences in recorded CUD times. Recent studies have suggested that elderly individuals show a reduction in size of the corpus callosum, particularly in the anterior region. In order to assess any potential change in callosal transfer efficiency with aging. CUDs were obtained from elderly (60+ years) and younger subjects (18 30 years). The elderly subjects showed a significantly elongated CUD compared to younger subjects, with elderly females contributing the greatest increase. No significant gender differences were found for younger subjects. In addition, an unexpected trend for an overall right field reaction time advantage was found for all subgroups, accompanied by a larger calculated CUD for right hand responses than for left hand responses.