Different geniculate inputs to B and C cells of cat striate cortex.

Cells with uniform receptive fields were selected for extra cellular recording in the striate cortex of anaesthetised cats. From their responses to electrical stimulation at three sites in the primary visual pathway the cells were grouped according to their ordinal position and whether their afferent drive came from the brisk sustained or brisk transient type of LGN neuron. From differences in laminar distribution and afferent stream the population was divided into 4 subgroups. Within these 4 subgroups there were two basic visual response patterns, which had been identified previously, and attributed to B and C cells. The B cells, which have a smaller receptive field, a lower spontaneous activity and cut-off velocity than C cells, were found to receive their input from slowly conducting afferents while the afferents to C cells arose from the fast stream. A high proportion of both B and C cells received a monosynaptic or direct drive from the optic radiations and responded with multiple spiking to a single electrical shock. Multiple spiking was viewed as evidence of secondary pathways travelling via intermediate cortical neurons to contribute to the cell's input. An examination of the visual properties of all subclasses showed that the more obvious differences in receptive field properties were associated with the type of afferent coming from the LGN rather than with the ordinal or the laminar position of the cell. In this respect the cells in the C/B family resemble S cells, whose receptive field properties also show a dependence on the type of LGN input.