EEG-fMRI combination for the study of visual perception and spatial attention

Electrophysiological recordings have defined the time-course of visual perception and attentional selection processes with a high degree of precision, but the anatomical localization of the underlying neural activity can only be approximated on the basis of surface recordings. In order to improve the accuracy of localizing the neural sources of the visual-evoked potentials (VEP) and event-related potentials (ERP) components, many recent studies have combined surface recordings with the spatially more precise hemodynamic measures provided by functional magnetic-resonance imaging (fMRI). In studies of visual perception and spatial attention that combined electrophysiological recordings with fMRI it was found that sensory-evoked activity is enhanced by attention, but the earliest component, which has been attributed to a primary visual cortex (V1) generator, was not affected by attention, but later components were enhanced in multiple areas of visual cortex including V1 (reentrant activity) and motion area V6.