Feed-forward, feedback and lateral interactions in membrane potentials and spike trains from the visual cortex in vivo.

Neurons in the visual cortex receive input from the lateral geniculate nucleus (feed-forward), higher order visual areas (feedback) and local neurons in the surroundings (lateral interactions). Here we first briefly review the approximate timing and proportion of these three types of influences on the membrane potentials in visual areas 17, 18 and 19. Then we present original results from an independent component analysis of multiunit spike trains in the same visual areas to resolve the contribution from these three sources. We stimulated the visual cortex of the ferret with a small transient contrast square stimulus and recorded the multiunit activity in areas 17, 18 and 19 with single or multiple electrodes. The spike trains had three reproducible components having their maxima at 40, 55 and 105ms after the start of the presentation of the stimulus. The time course of the third component was significantly correlated with the population membrane potential in the supragranular layers of areas 17, 18 and 19. The first spike train component was interpreted as a feed-forward response, the second spike train component as driving the laterally spreading depolarization and the third spike train component as the firing caused by the lateral spreading- and the feedback depolarization.