Color tuning of neurons in face patches of macaque inferior temporal cortex

Abstract

How are face-specific color signals encoded by the brain? We addressed this question by measuring color responses of face-selective cells in alert macaque monkey, using fMRI-guided microelectrode recording of the middle and anterior face patches. Many face-selective neurons showed broad color tuning when assessed using images that preserved the luminance contrast relationships of the original face photographs. A Fourier analysis of the color-tuning responses uncovered two components. The first harmonic showed a bias towards the L>M pole of the L-M cardinal axis of cone-opponent color space (appearing reddish), which suggests that face cells encode a prior about the color component of faces that is important for social signaling (blood perfusion). The second harmonic showed a bias for colors that modulate the S-cone cardinal axis, which may relate to the computation of animacy by IT cells. Taken together, these results uncover a putative physiological basis for the role of color in face perception and show that chromatic signatures corresponding to the cardinal chromatic mechanisms are evident not only in subcortical circuits, as previously known, but also far along the visualprocessing hierarchy, within inferior temporal cortex.Significance: It is not known how the brain processes combined color and face information. The present results fill this gap in knowledge by uncovering the color tuning properties of face-selective neurons. The results further our understanding of the neural mechanisms that make color an informative cue for social communication.