Neural Response Interactions in Early Cortical Processing during a Simple Reaction Time Task

Abstract:
Abstract: High-density electrical mapping using visual evoked potentials (VEPs) in 15 subjects investigated the latency when neural responses to stimulus pairs interact during a simple reaction time task. We compared the algebraically summed VEPs to single stimuli displayed in one quadrant with those to stimulus pairs simultaneously displayed in two quadrants (either bilaterally or unilaterally). These should be equivalent so long as neural responses to each of the single stimuli remain independent. Divergence indicates response interactions between the stimuli. In each visual field interactions were observed by 86ms over parieto-occipital scalp sites, earlier than previously observed during passive viewing. We also asked whether peak P1 latency of the VEPs tracks the redundant target effect (RTE - reaction time facilitation for stimulus pairs versus single stimuli). We found that peak P1 latency does not track the RTE. For bilateral conditions peak P1 latency from stimulus pairs was later than or simultaneous with that for the faster of the single stimuli. This pattern held for the unilateral conditions over 'direct projection' scalp sites (i.e. those contralateral to the stimulated visual field). Over 'indirect projection' scalp sites peak P1 latency for stimulus pairs was significantly earlier than for either the single stimulus or summed responses.