Magnetoencephalographic investigation of human cortical area V1 using color stimuli

The aim of this study was to determine the response properties of the human visual cortex to chromatic stimuli using magnetoencephalography (MEG). Evoked responses were recorded to isoluminant red/green sinusoidal gratings for a wide range of spatial and temporal frequencies. For each condition the response was dominated by a single major component which was well modeled by an equivalent current dipole. Coregistration of MEG and MRI data provided evidence that the principal evoked cortical activity originated from visual area V1. To investigate the chromatic response properties of this area, the maximum global field power of the evoked response was plotted as a function of stimulus spatial and temporal frequency. The spatial-frequency tuning was lowpass and the temporal-frequency tuning was multimodal, with peaks at 0 and 4 Hz. The results demonstrate the use of MEG as a technique for investigating activity from discrete regions of cortex.