Simultaneous recordings of visual evoked potentials and BOLD MRI activations in response to visual motion processing.

Visual motion processing in humans was studied by simultaneous 32-channel electroencephalography (EEG) recordings of visual evoked potentials and BOLD MRI activations at 2.9 T. The paradigms compared three different random dot patterns (12 s duration) with stationary random dots (18 s) or with each other. The stimuli represented pattern reversal (500 ms switches between two stationary patterns), motion onset (200 ms of starfield motion followed by 1000 ms of stationary dots) and motion reversal (reversal of moving starfield directions every 1000 ms). Whereas motion-evoked visual potentials, and in particular the N2 component in occipito-temporal channels, were most prominent for motion onset, the most extended BOLD MRI activations and strongest signal changes in V5/MT+ were obtained in response to motion reversal. These apparently contradictory findings most likely reflect different physiological aspects of the neural activity associated with visual motion processing. For example, desynchronized activity of subpopulations of cortical neurons inside V5/MT+ is expected to attenuate visual evoked potentials in scalp recordings while continuously driving metabolic demands that lead to sustained BOLD MRI responses. The understanding of the physiological correlates and neural processes underlying either technique is fundamental to exploring fully the potential of combined EEG-MRI for studying human brain function at both high temporal and spatial resolution.