We thank John Maunsell for invaluable discussions and suggestions for data analysis; Geoffrey Ghose, Jonathan Horton, and Jon Kaas for helpful comments on the manuscript; and Lara Hinderstein and Carmela LoRusso for excellent technical support.

Visual area V4 is a midtier cortical area in the ventral visual pathway. It is crucial for visual object recognition and has been a focus of many studies on visual attention. However, there is no unifying view of V4’s role in visual processing. Neither is there an understanding of how its role in feature processing interfaces with its role in visual attention. This review captures our current knowledge of V4, largely derived from electrophysiological and imaging studies in the macaque monkey. Based on recent discovery of functionally specific domains in V4, we propose that the unifying function of V4 circuitry is to enable selective extraction of specific functional domain-based networks, whether it be by bottom-up specification of object features or by top-down attentionally driven selection.

Retinal cells have been induced to project into the medial geniculate nucleus, the principal auditory thalamic nucleus, in newborn ferrets by reduction of targets of retinal axons in one hemisphere and creation of alternative terminal space for these fibers in the auditory thalamus. Many cells in the medial geniculate nucleus are then visually driven, have large receptive fields, and receive input from retinal ganglion cells with small somata and slow conduction velocities. Visual cells with long conduction latencies and large contralateral receptive fields can also be recorded in primary auditory cortex. Some visual cells in auditory cortex are direction selective or have oriented receptive fields that resemble those of complex cells in primary visual cortex. Thus, functional visual projections can be routed into nonvisual structures in higher mammals, suggesting that the modality of a sensory thalamic nucleus or cortical area may be specified by its inputs during development.

Visual area V4 in the macaque monkey is a cortical area strongly involved in shape and color perception. However, fundamental questions about V4 are still debated. V4 was initially characterized as a color processing area but subsequent studies revealed that it contains a diverse complement of cells, including those with preference for color, orientation, disparity, as well as higher order feature preferences. This has led to disputes and uncertainty about the role of V4 in vision. In this study, using intrinsic signal optical imaging methods in awake, behaving monkeys, we demonstrate functional organization for different feature preferences within V4. Optical images reveal that regions with preferential response to color or luminance are largely separate from orientation selective regions. These results help resolve long-standing controversies regarding functional diversity and retinotopy within V4 and indicate the presence of spatially biased distribution of featural representation in V4 in the ventral visual pathway.

SUMMARY Studies of resting state activity in the brain have provoked critical questions about the brain’s functional organization but, its biological basis is not clear. Specifically, the relationships between interregional correlations in resting state measures of activity, neuronal functional connectivity and anatomical connectivity are much debated. To investigate these relationships, we have examined both anatomical and steady state functional connectivity within the hand representation of primary somatosensory cortex (areas 3b and 1) in anesthetized squirrel monkeys. The comparison of three data sets (fMRI, electrophysiological, anatomical) indicate two primary axes of information flow within SI: prominent interdigit interactions within area 3b and predominantly homotopic interactions between area 3b and area 1. These data support a strikingly close relationship between baseline functional connectivity and anatomical connections. This study is also the first to extend findings derived from large-scale cortical networks to the realm of local mm-scale networks.