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

Abstract

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.

Representation of the Material Properties of Objects in the Visual Cortex of Nonhuman Primates

“…Each monkey was extensively trained to perform a fixation task in a mock scanner environment. Detailed descriptions of the surgery and training are provided previously (Harada et al, 2009;Okazawa et al, 2012). All experimental procedures were in accordance with NIH guidelines and were approved by the Animal Experiment Committee of Okazaki National Research Institutes.…”

“…Because the monkeys were overtrained for fixation, the performances during scanning were generally good. The monkey's eye position was continuously recorded using an eye-tracking system based around an infrared CCD camera (60 Hz; Sony), and the task was controlled using custom-made software (Harada et al, 2009;Okazawa et al, 2012).…”

“…A high-resolution anatomical image (MPRAGE; 0.5 mm isovoxel) was collected from each monkey under anesthesia in a separate scanning session (Harada et al, 2009;Okazawa et al, 2012) and the cortical surface was reconstructed from this image using CARET (http://www.nitrc. org/projects/caret/).…”

“…The material image (7.5°ϫ 7.5°), in which an elongated virtual object subtending ϳ4.5°width and 7.5°height was placed at the middle, was presented in the center of a uniform gray background (26°ϫ 20°). The stimulus was displayed using a calibrated projection display system (Harada et al, 2009;Okazawa et al, 2012).…”

Functional localization of the human color center by decreased water displacement using diffusion‐weighted fMRI

“…2009). Here, it was shown that DfMRI also reveals the color center using this cognitive subtraction paradigm.…”