COMBINING STEADY-STATE VISUAL-EVOKED POTENTIALS AND FMRI TO LOCALIZE BRAIN ACTIVITY DURING SELECTIVE ATTENTION

Brain activity was studied with fMRI and steady-state visual evoked po tentials (SSVEPs) in separate sessions as subjects attended to letter sequences in either the right or left visual field. The two letter seq uences were superimposed on small square backgrounds that flickered at 8.6 and 12.0 Hz, respectively, and elicited SSVEPs at the flicker fre quencies. The amplitude of the frequency-coded SSVEP elicited by eithe r of the flickering backgrounds was enlarged when attention was focuse d upon the letter sequence at the same location. Source analysis of th e SSVEP waveforms localized the attentional modulation to ventral and lateral extrastriate visual cortex, which corresponded to zones of act ivation observed with fMRI. (C) 1997 Wiley-Liss, Inc.