Identification of the cortical sources of the pattern-reversal VEP

This study aimed to characterize the neural generators of the early components of the visual-evoked potential (VEP) to pattern-reversal gratings. Multichannel scalp recordings of VEPs and dipole modeling techniques were combined with functional magnetic resonance imaging (fMRI) and retinotopic mapping in order to estimate the locations of the cortical sources giving rise to VEP components in the first 200 ms poststimulus. Dipole locations were seeded to visual cortical areas in which fMRI activations were elicited by the same stimuli. The results provide strong evidence that the first major component of the VEP elicited by a pattern-reversal stimulus (N75/P85) arises from surface-negative activity in the primary visual cortex (area V1). Subsequent waveform components could be accounted for by dipoles that were in close proximity to fMRI activations in the following cortical areas: P95 (area MT/V5), P125/N135 (area V1), N150 (transverse parietal sulcus, TPS), N160 (ventral occipital areas VP, V4v, and V4/V8), and N180 (dorsal occipital areas V3A/V7). These results provide a detailed spatiotemporal profile of the cortical origins of the pattern-reversal VEP, which should enhance its utility in both clinical and basic studies of visual-perceptual processing.