Lamina-specific differences of visual latencies following photic stimulation in the cat striate cortex

Vertical penetrations were made in the part of the cat's area 17 subserving central vision. Single units were recorded every 100-200 micron and the recording sites histologically reconstructed. Visual latencies of complex cells following whole-field ON/OFF stimulation were determined as a function of cortical depth. The shortest latencies were found for cells in layers IV and VI (mean ON response 44 ms/OFF response 51 ms for IV and 43 ms/42 ms for VI). In contrast, mean latencies in layer V were 54 ms/57 ms, while cells of the supragranular layers had the longest mean latencies of 62 ms/73 ms. Furthermore, this analysis revealed significant differences of between 10 and 30 ms on the average between the individual layers (the differences between individual cells can even be in the range of more than 60 ms). These differences cannot easily be explained by conduction time and synaptic delays, which both can account for a few ms only. One possible explanation is based on a dynamic model of intracortical information processing with multiple positive feedback loops.