Brain mapping of bilateral visual interactions in children

Interhemispheric interactions were studied with functional brain mapping of visual processing. Children performed a reaction time task with uni- and b ilateral targets and nontargets. The visual evoked potential (VEP) was segm ented into P1a, P1b, and N1 microstates using map rather than channel featu res. Map latencies, amplitudes and sources were tested for bilateral intera ctions. Bilateral targets yielded shorter VEP map latencies but later respo nse onsets than unilateral ones. Source analyses of the unilateral VEPs ind icated a transition from contra- (P1a) to ipsilateral (P1b) visual cortex a ctivation (interhemispheric transfer). Bilateral VEPs were smaller than the summed unilateral VEPs in all microstates, indicating that interhemispheri c interactions both precede and follow interhemispheric transfer. Brain map ping of uni-and bilateral VEPs in children thus revealed several distinct f orms of interhemispheric interactions in the same, early time range.