Morphology of physiologically identified neurons in the visual cortex of the cat

Most cells in cortical area 17 of the cat can be physiologically classified as simple or complex 3,13A6. Both types of cells are found virtually in every layer, but simple cells are concentrated in layer IV, while complex cells are more frequently recorded in layer V2,3, s. Anatomical studies indicate that stellate cells occur most frequently in layer IV, and pyramidal cells are found in other layers9,10,14. Thus, the stellate cells may have simple receptive fields; and pyramidal cells, complex receptive fields. Kelly and Van Essen related neuronal structure to function with a more direct technique 5. They impaled physiologically identified cells and filled them with the dye, Procion yellow. From this, they concluded that most complex cells are morphologically pyramidal, whereas most simple cells are not. We re-investigated this problem using horseradish peroxidase (HRP), instead of a fluorescent dye, to stain the ce111,4, 6. This seemed to give a more complete morphological picture than can generally be obtained with Procion dyes. Our preliminary observations generally support those of Kelly and Van Essen 5, but some details have been added. Normal adult cats were used for these studies. The physiological preparation, anesthesia, and recording techniques have been described previously 1,1~,16, with minor exceptions noted as follows. Micropipettes were filled with 2-3 ~o HRP in 0.2 M KC1, buffered with 0.05 M Tris at pH 8.6, and their tips were bevelled (100-200 Mf~ at 200 Hz; o.d. < 0.5/~m). The electrode was inserted vertically into the medial wall of area 17. Cells were isolated extracellularly and classified as simple or complex3,13,16. We then advanced the electrode in 1 /zm steps to impale the neuron. Intracellular recording was verified by previously published criteria (ref. 1 ; see also Fig. 1A, C of this report), and we re-examined the physiological properties to verify that the cell was the same as classified extracellularly. Next, we injected HRP into the cell by