Local circuits in primary visual cortex of the macaque monkey.

The basic laminar organization of excitatory local circuitry in the primary visual cortex of the macaque monkey is similar to that described previously in the cat's visual cortex (Gilbert 1983). This circuitry is described here in the context of a two-level model that distinguishes between feedforward and feedback connections. Embedded within this basic framework is a more complex organization. Within the strictly feedforward pathway, these circuits distribute unique combinations of magno-, parvo-, and koniocellular input from the lateral geniculate nucleus (LGN) to neurons in layers 2-4B. Their input is dependent on the extrastriate cortical areas they target. The local feedback connections from deep layers (5 and 6) arise from a diverse population of pyramidal neurons. Each type forms local connections with a unique relationship to more superficial layers. In the case of layer 6 neurons, these connections are closely related to layer 4 subdivisions receiving input from different functional streams.