Hierarchical organisation and neuronal response latencies in the primate visual system

While the anatomical connectivity of the macaque visual system is organized hierarchically, many dorsal cortical visual areas respond nearly simultaneously to flashed stimuli. Does this contradict hierarchical processing? To address this issue, we constructed an integrate-and-fire network, consisting of M and P layers of LGN, and of several visual cortical areas for which latency data were available. The neural network implemented the areas' known laminar connectivity. The model displayed simultaneous onset of activity in several dorsal stream areas, closely matching experimental observations. Thus, anatomical organization and neurophysiological data are not contradictory, and hierarchical processing does not imply sequential response timing.