Local circuit neurons of macaque monkey striate cortex: IV. Neurons of laminae 1-3A.

We continue our Golgi studies (Lund [1987] J. Comp. Neurol. 257:60-92; Lund et al. [1988] J. Comp. Neurol. 276:1-29; Lund and Yoshioka [1991] J. Comp. Neurol. 331:234-258) of the organization of local circuit, largely gamma-aminobutyric acid (GABA)-containing neurons in macaque monkey visual cortex, area V1, with this account of the local circuit neurons lying in layers 1 and 2/3A. These layers receive intrinsic interlaminar excitatory and inhibitory relays from layers 3B, 4A, 4B, and 5. We describe seven varieties of local circuit neurons with somata within layers 1-2/3A, and we compare the lateral scale of spread of the axons and dendrites of these neurons with the size of the columnar connectional patch domains made by the laterally spreading axon collaterals of pyramidal neurons within the superficial layers (Lund et al. [1993] Cerebral Cortex 3:148-162). We conclude from this comparison that all of the neurons have dendritic fields that are limited to single patch domains. Furthermore, only two of the seven local circuit neuron varieties have sufficient axon spread to influence territory beyond single domains, reaching into neighboring territory likely to differ in function from that occupied by their dendrites. We have identified descending projections from particular varieties to layers 3B, 4A, 4B, and 5 and to the white matter. We discuss the contributions that these interneurons may make to function within the superficial cortical layers, and we summarize our overall conclusions, so far, from our set of studies on interneurons within area V1 of the macaque.