Colour coding in rhesus monkey prestriate cortex

Abstract

One of the striking features o f the anatomical organisation o f the prestriate cortex in the monkey is the mosaic o f sub-areas into which it may be divided on the basis of the afferent input, efferent output and inter-hemispheric connections of its individual partsl , 5-s. Such a mosaic organisation no doubt reflects a functional division of labour within the prestriate cortex for handling the various parameters o f vision, the emphasis on any particular function in any particular area being presumably dictated by the organisation of the afferent input to that area. The topographically organised pointto-point input f rom the lateral geniculate nucleus to area 17 is reflected functionally in the detailed region-by-region form analysis that this area performs 4. On the other hand, the overlapping, convergent input f rom area 17 to the cortex o f the posterior bank of the superior temporal sulcus is reflected functionally in the generalisation for receptive field position and the emergence o f movement as a critical stimulus parameter 2. In this paper, we report briefly the response properties o f units to simple visual stimulation in another prestriate area, the fourth visual area (V4) which we have already defined anatomically 7. This area lies in the anterior bank of the lunate sulcus dorsally and, because of the complicated gyral changes, emerges ventrally in the posterior bank of the inferior occipital sulcus 7. It receives an input f rom areas 18 and 19 but this projection does not appear to be very precisely defined topographically. We have recorded f rom 77 single units in this area, in 8 monkeys, using tungsten-inglass microelectrodes, and in every case the units have been cotour coded, responding vigorously to one wavelength and grudgingly, or not at all, to other wavelengths or to white light at different intensities. The animals were anaesthetised with sodium pentobarbital and paralysed with gallamine triethiodide (5 mg/kg/h). A hole was drilled in the skull over the appropriate