Visual activation of frontal cortex: segregation from occipital activity

Studies in primates have found visually responsive neurons that are distrib uted beyond cortical areas typically described as directly involved in visi on. Among these areas are premotor cortex, supplementary motor area, dorsol ateral prefrontal cortex and frontal eye fields. Given these findings, visu al stimulation would be expected to result in activation of human frontal c ortex. However, few human studies have described sensory activations in fro ntal regions in response to simple visual stimulation. Such studies have cl assically described event-related potential (ERP) components over occipital regions. The present study sought to further characterize the spatiotempor al dynamics of visually-evoked electrocortical responses elicited by simple visual stimuli using scalp current density measures derived from high-dens ity ERP recordings, with particular emphasis on the distribution of stimulu s-related activity over frontal cortex. Hemiretinal stimuli were viewed pas sively and during a simple ipsi- or contramanual (RT) task. The motor requi rement was included to investigate the effects of response preparation on p removement frontal activations. The results indicate early frontocentral ac tivation, particularly over the right hemisphere (peak magnitude 124-148 ms ) that is independent of input visual field or motor response requirement, and that is clearly separate in timecourse from the posterior responses eli cited by visual input. These findings are in accord with the multiplicity o f visual inputs to frontal cortex and are discussed in terms of frontal lob e functions as may be required in these tasks. (C) 2001 Elsevier Science B. V. All rights reserved.