Responses to colour of neurones in area 7a of the inferior parietal lobule of the rhesus monkey.

A single-unit study on area 7a of alert, fixating rhesus monkeys revealed responsiveness to primary colours comparable to white light responsiveness shown in other cells. Mostly decremented, some biphasic, and a small portion with incremented neuronal firing response were observed, following stimulation of cells by parafoveal receptive field, rectangular, approximately 20 degrees x 20 degrees red, green or blue-violet light stimuli. The same cell showed no response to white light. Receptive fields of these colour-sensitive cells, like those of white-sensitive cells, were mostly contralateral, some ipsilateral and a few in both hemifields. Augmentation of responses following preconditioning electrical stimulation of lateroposterior-pulvinar targets was observed as with the white-light sensitive cells. It is noteworthy that this monkey area 7a colour sensitivity is complementary to previously demonstrated white light sensitivity. The specific properties revealed by these cells suggest separate channels within area 7a for colour and for achromatic light, the colour sensitivity possibly relevant when chromaticity is of generalized import, and these may subserve the animal's orienting response to colour appearance in the near-periphery visual field.