Distribution of colour-selective activity in the monkey inferior temporal cortex revealed by functional magnetic resonance imaging.

Previous electrophysiological, neuroimaging and lesion studies have suggested that the anterior part of the monkey inferior temporal (IT) cortex, or area TE, plays an important role in colour processing. However, little is known about how colour information is distributed in these cortical regions. Here, we explored the distribution of colour-selective activity in alert macaque monkeys using functional magnetic resonance imaging (fMRI) with two types of stimuli: a multicoloured ('Mondrian') pattern and an isoluminant colour grating. These two types of stimuli are both commonly used in human fMRI studies, but Mondrian stimuli, which contain a richer variety of hues and hence might be more suitable for activating higher-order areas than grating stimuli, have not been used to examine colour-selectivity in higher-order areas in earlier monkey studies. With the Mondrian stimuli, we observed that areas along the ventral pathway, V1, V2/V3, V4 and the IT cortex, responded more strongly to colour stimuli than to luminance stimuli. In the IT cortex, we found that colour-selective activities are not distributed uniformly, but are localized in discrete regions, each extending several millimetres in the anterior or posterior part of the IT cortex. The colour-selective activation in the anterior IT was observed only with the Mondrian stimuli, whereas the colour-selective activation in the posterior IT was observed with both the Mondrian and grating stimuli, with little overlap. These findings suggest that there are multiple subregions with differing stimulus selectivities distributed in the IT cortex, and that colour information is processed in these discrete subregions.