Multiple Loci for Foveolar Vision in Macaque Monkey

Abstract

A common tenet of neural sensory representation is that species-specific behaviors are reflected in specialized brain organizations. In humans and nonhuman primates, the central one degree of vision is processed by the foveola, a retinal structure which comprises a high density of photoreceptors and is crucial for primate-specific high acuity vision, color vision, and gaze-directed visual attention. In this study, we have developed high spatial resolution ultrahigh field 7T fMRI methods for functional mapping of foveolar visual cortex in awake monkeys. We provide evidence that, in the ventral pathway (V1-V4 and TEO), viewing of a central small spot elicits a ring of multiple (at least 8) foveolar representations per hemisphere. This ring surrounds a large area called the "foveolar core". This is an area populated by millimeter-scale functional domains sensitive to fine stimuli and high spatial frequencies, consistent with foveolar visual acuity, as well as color and achromatic information, and motion. The unique position of the foveolar core suggests it may be a hub subserving higher order needs of foveolar function, such as integrating different spatial scales of representation, integrating local and global features in object perception, and bringing together the four quadrants of visual space. Thus, this elaborate re-representation of central vision signifies a cortical specialization for various foveation behaviors.