Striate cortical cells were classified according to whether or not their preferred orientation was close to one of the “primary” orientations (horizontal, vertical or radial, i.e. directed to the area centralis) and according to their ordinal position on the afferent pathway from the dorsal lateral geniculate nucleus (dLGN). Among the neurones that could be driven monosynaptically from the dLGN, there was a high representation of those with a preference for the primary orientations. This was particularly evident in the case of C (complex) cells. There was no such preponderance of primary orientations among the polysynaptically activated cells. It is proposed that the asymmetry of distribution seen among the first-order cells reflects the asymmetry seen subcortically in neurones that show orientation biases. It may be that the cortex elaborates a more uniform representation of orientations only at the higher ordinal levels.
