Topography of averaged electrical brain activity relating to interhemispheric dynamics in normal humans: where does the critical relay take place?

Interhemispheric relay time (IHRT) was investigated using a 16-electrode mo ntage in 10 normal subjects during a simple visual reaction time task (Poff enberger paradigm). The P1 latency was the dependent measure. Response-lock ed components were separated from the stimulus-locked components based on t he reaction times using a Woldorff-like filter. The issues of theoretical i nterest were the following: (1) does the responding hand modulate MRT estim ates as a function of electrode site, or stimulated field?; (2) what are th e respective advantages of various pairs of symmetrical across-midline elec trode sites for tracking IHRT?; and (3) what are the respective advantages of symmetrical vs. asymmetrical across-midline electrode site-pair configur ations for tracking IHRT? There were significant lags attributable to IHRT in both evoked potential PI latencies and in reaction times - but these wer e uncorrelated. The responding hand was not found to significantly modulate IHRT estimates derived from the P1 peak latency of response-corrected ERPs : Anterior sites yielded more precocious components and briefer estimates o f IHRT which were closer to those observed in reaction time estimates. Howe ver, posterior leads yielded more reliable estimates. Various analyses sugg ested that IHRT can be tracked, very vaguely, with asymmetric configuration s as well as symmetric ones, each for different reasons. (C) 1999 Elsevier Science B.V. All rights reserved.