Shape and arrangement of columns in cat's striate cortex.

Cells in the cat's striate cortex show marked specificity in their responses to restricted retinal stimulation (Hubel & Wiesel, 1959, 1962). The most effective stimulus shapes are long narrow rectangles of light ('slits'), dark bars against a light background ('dark bars'), and straight-line borders separating areas of different brightness ('edges'). A given cell responds vigorously when an appropriate stimulus is shone on the receptive field or moved across it, provided the stimulus is presented in a specific orientation. This orientation is termed the 'receptive-field axis orientation'. It is critical, and constant for any particular cell, but may differ for different cells. The visual cortex is subdivided into discrete regions or columns extending from surface to white matter, in which all cells have the same receptivefield axis orientation (Hubel & Wiesel, 1962). The present experiments were undertaken with the object of learning more about the anatomical configuration of the columns. We wished to have a clearer idea of their shape, especially if the walls of a column were, as previous work suggested, parallel to the radial fibre bundles of the cortex and perpendicular to the cortical layers, and whether the columns were uniform or irregular in their cross-sectional shape and size. Furthermore, we were curious to know if there was any relationship between the receptive-field axis orientations of neighbouring columns, or whether, on the contrary, the different columns were intermixed in a random way throughout the cortex. These questions were approached: (1) by making several deep, closely spaced, parallel micro-electrode penetrations, placing electrolytic lesions at every shift in receptive-field orientation, and(2) by making many short penetrations in a small cortical area, noting the axis orientation of cells lying in the upper one or two layers of cortex.