Visual receptive fields of local intracortical potentials.

We have developed a method to define a spatial-temporal receptive field (RF) for local, intracortically recorded field potentials in the visual cortex. In analogy to the classic RF concept, a relation between stimulus position and a single recording location is evaluated. Our receptive field cinematogram (RF-Cine) approach, additionally, includes the temporal dynamics between stimulus and response: A sequence ('movie') of successive 'frames' is calculated, which shows the field potential amplitudes plotted with reference to the position in visual space of a randomly moving stimulus. The exploration of the receptive fields via a randomly jumping disk stimulus is especially suitable for multi-electrode cortex mapping, because the RF-Cines of all electrodes can be evaluated simultaneously within a single stimulation period of 100 s duration. Field potential RF-Cines showed concentrical or ellipsoidal antagonistic center-surround structures with biphasic or triphasic time courses. The size of these structures increases with retinal eccentricity. The cortical surface coverage of the RF-Cine centers was calculated to be 0.8 mm2 for area 17 and 1.3 mm2 for area 18, being nearly constant within the 0-10 degrees cortical representation of the lower visual field. These values approximately correspond to the extent of one hypercolumn. The absolute positions of the RF-Cine structures can be determined with an accuracy of 0.1-0.2 mm in cortical coordinates.