Specialized Color Modules in Macaque Extrastriate Cortex

Abstract

Imaging studies are consistent with the existence of brain regions specialized for color, but electrophysiological studies have produced conflicting results. Here we address the neural basis for color, using targeted single-unit recording in alert macaque monkeys, guided by functional magnetic resonance imaging (fMRI) of the same subjects. Distributed within posterior inferior temporal cortex, a large region encompassing V4, PITd, and posterior TEO that some have proposed functions as a single visual complex, we found color-biased fMRI hotspots that we call "globs," each several millimeters wide. Almost all cells located in globs showed strong luminance-invariant color tuning and some shape selectivity. Cells in different globs represented distinct visual field locations, consistent with the coarse retinotopy of this brain region. Cells in "interglob" regions were not color tuned, but were more strongly shape selective. Neither population was direction selective. These results suggest that color perception is mediated by specialized neurons that are clustered within the extrastriate brain.

Color-tuned neurons are spatially clustered according to color preference within alert macaque posterior inferior temporal cortex

“…All of the cells whose responses are shown in Fig. 1 not only were significantly colortuned, but also retained this color tuning across changes in luminance, a common feature of glob cells (7). Some 96% (303/312) of the recorded glob cells were color-tuned (Fig.…”

“…Color-biased regions in PIT were identified using fMRI as described previously (7,16). These globs are defined as those regions that show greater fMRI activation to equiluminant color stripes versus black-and-white stripes.…”

“…Experimental procedures for fMRI in alert macaques are available elsewhere (22,35). Globs were identified using procedures described previously (7). Two macaque monkeys were trained for a juice reward to fixate a visual display while the animals were situated in a chair fit for a Siemens 3T horizontal-bore scanner.…”

“…Large (millimeter-sized) color modules have been found downstream of V2 using functional MRI (fMRI) and confirmed using single-unit recording (7). We refer to these modules as ''globs,'' to distinguish them from other sorts of modules found in other regions of the cortex (e.g., face patches, inferior temporal feature columns).…”

Mapping of functional brain activity in freely behaving rats during voluntary running using manganese-enhanced MRI: Implication for longitudinal studies

“…Such studies are now becoming feasible for non-human primates (Conway et al, 2007;Goense et al, 2008;Kayser et al, 2007;Maier et al, 2008;Op de Beeck et al, 2008), but still remain a challenge for application in alert and behaving rodents, the most commonly used experimental animals. One reason for that is that the majority of behavioral paradigms developed for rodents often require active locomotion as a behavioral expression of a particular cognitive function.…”