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 montage in 10 normal subjects during a simple visual reaction time task (Poffenberger paradigm). The P1 latency was the dependent measure. Response-locked components were separated from the stimulus-locked components based on the reaction times using a Woldorff-like filter. The issues of theoretical interest were the following: (1) does the responding hand modulate MRT estimates as a function of electrode site, or stimulated field?; (2) what are the respective advantages of various pairs of symmetrical across-midline electrode sites for tracking IHRT?; and (3) what are the respective advantages of symmetrical vs. asymmetrical across-midline electrode site-pair configurations for tracking IHRT? There were significant lags attributable to IHRT in both evoked potential PI latencies and in reaction times - but these were 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 of IHRT which were closer to those observed in reaction time estimates. However, posterior leads yielded more reliable estimates. Various analyses suggested that IHRT can be tracked, very vaguely, with asymmetric configurations as well as symmetric ones, each for different reasons. (C) 1999 Elsevier Science B.V. All rights reserved.