Laminar differences in response characteristics of cells in the primary visual cortex

Michael Jacob
University of California, Berkeley

There are two primary organizing features of the cerebral cortex; columnar structure and distinct lamina. A central goal of cortical study is to understand local neural circuits within this organization. We used a database from 50 cats to study the properties of 852 neurons in the primary visual cortex. Cortical location and laminar positions were determined from careful analysis of digital reconstructions of tissue stained for Nissl. In classical descriptions, input layers (4a, 4b and 6) are considered to be nearly entirely composed of simple cells. On the contrary, we find large numbers of complex cell types in these layers. Layers 4a and 6 contain around 40% complex cells and layer 4b contains over 50% complex cells. Furthermore, layers 2/3 and 5, which are classically considered complex layers, contain 55% and 35% simple cells, respectively. The main input layers, 4a and 4b, contain the most broadly tuned cells for orientation, especially amongst cells with high levels of spontaneous activity. These results suggest an intracortical tuning refinement process, including possible roles for cells with high spontaneous activity levels.