Distribution and morphology of functionally identified neurons in the visual cortex of the rat

The distribution and morphology of functionally identified neurons were examined in the visual cortex of Long Evans pigmented rats. The results, based on qualitative and quantitative analysis of single cell spike activity, have shown that neurons in the rat visual cortex have well-defined receptive field properties and are similar to those reported for animals with more highly developed visual systems. Unlike the cat and monkey, the distribution of receptive field types appeared even throughout the visual cortex. Exception was provided by layer IV which, similar to the more 'visual' animals, contained the largest percentage of simple cells. Horseradish peroxidase injected into single, physiologically identified neurons allowed for detailed morphological characterization of functional cell types. Of the cells successfully filled with horseradish peroxidase, complex cells were pyramidal in morphology and located in layers II through VI. Simple cells were both pyramidal and non-pyramidal in appearance and were located in layers II + III and IV. Finally, hypercomplex cells were pyramidal in appearance and their perikarya were situated in layers II + III and V.