Brain mapping of bilateral visual interactions in children

Abstract

Interhemispheric interactions were studied with functional brain mapping of visual processing. Children performed a reaction time task with uni- and bilateral targets and nontargets. The visual evoked potential (VEP) was segmented into P1a, P1b, and N1 microstates using map rather than channel features. Map latencies, amplitudes and sources were tested for bilateral interactions. Bilateral targets yielded shorter VEP map latencies but later response onsets than unilateral ones. Source analyses of the unilateral VEPs indicated a transition from contra- (P1a) to ipsilateral (P1b) visual cortex activation (interhemispheric transfer). Bilateral VEPs were smaller than the summed unilateral VEPs in all microstates. indicating that interhemispheric interactions both precede and follow interhemispheric transfer. Brain mapping of uni- and bilateral VEPs in children thus revealed several distinct forms of interhemispheric interactions in the same, early time range.

Neural Correlates of the Left-Visual-Field Superiority in Face Perception Appear at Multiple Stages of Face Processing

“…This finding suggests that early occipital components over a given hemisphere mainly reflect processes carried out by that hemisphere and not by the opposite hemisphere (see also Steger et al, 2001, for a source localization analysis of occipital potentials to unilateral stimuli). Thus, the difference we observed between potentials to B and L faces over the RH, which project the same information to the RH but different information to the LH, reflects the influence of transcallosal data from the LH.…”

“…The difference in ERP amplitudes between contralateral and ipsilateral hemifaces, which was equal over the left and right hemispheres, F(1,11) < 1, suggests that occipital responses over the RH or the LH mainly reflect processes that are carried out by that hemisphere (see also Rugg, Milner, & Lines, 1985, for evidence from callosal agenesis patients and Steger et al, 2001, for source localization of early components to unilateral stimuli in normal subjects). Given that B faces and contralateral hemifaces project the same information to the contralateral hemisphere but different information to the ipsilateral hemisphere, the different brain potentials they elicit are likely to reflect the influence of transcallosal data.…”