Ventral Occipital Cortex Research Articles

Functional mapping of color processing by magnetic resonance imaging of responses to selective P- and M-pathway stimulation.

Magnetic resonance imaging sensitized to activity-related changes in cerebral blood oxygenation was performed to map responses to selective stimulation of the parvo- and magnocellular visual pathways in calcarine and adjacent ventral occipital cortex of human subjects. In a repetitive stimulation protocol isoluminant chromatic or isochromatic luminance modulation was alternated with steady light of the same mean chromaticity and luminance as a reference condition. While no significant effects were observed for diffuse luminance modulation, two consistent cortical foci responded to isoluminant chromatic stimulation. A strong response was obtained in calcarine cortex at both 2 and 10 Hz, and even for selective S-cone stimulation. A second weaker color-sensitive response was seen bilaterally in the collateral sulcus. Thus, the data not only confirm color-sensitive activation in the collateral sulcus elicited in previous studies by selective cognitive tasks, but additionally demonstrate color-sensitive activation in primary visual cortex. With stimuli defined according to electrophysiological response properties of early visual processing stages, this study complements phenomenological or cognitive approaches in functional mapping of the human visual system.

Visual topography of area TEO in the macaque

Previous studies have mapped the visuotopic organization of visual areas from V1 through V4 in the occipital cortex and of area TE in the temporal cortex, but the cortex in between, at the occipito-temporal junction, has remained relatively unexplored. To determine the visuotopic organization of this region, receptive fields were mapped at 1,200 visually responsive sites on 370 penetrations in the ventral occipital and temporal cortex of five macaques. We identified a new visual area, roughly corresponding to cytoarchitectonic area TEO, located between the ventral portion of V4 and area TE. Receptive fields in TEO are intermediate in size between those in V4 and TE and have a coarse visuotopic organization. Collectively, receptive fields in TEO appear to cover nearly the entire contralateral visual field. The foveal and parafoveal representation of TEO is located laterally on the convexity of the inferior temporal gyrus, and the peripheral field is represented medially on the ventral surface of the hemisphere, within and medial to the occipitotemporal sulcus. Beyond the medial border of TEO, within cyteoarchitectonic area TF, is another visually responsive region, which we have termed VTF; this region may also have some crude visual topography. Bands of constant eccentricity in TEO appear to be continuous with those in V2, V3v, and V4. The upper field representation in TEO is located adjacent to that in ventral V4, with a representation of the horizontal meridian forming the boundary between the two areas. The lower field representation in TEO is located just anterior to the upper field but is smaller. In contrast to the orderly representation of eccentricity in TEO, we found little consistent representation of polar angle, other than the separation of upper and lower fields. The results of injecting anatomical tracers in two animals suggest that TEO is an important link in the pathway that relays visual information from V1 to the inferior temporal cortex. TEO is thus likely to play an important role in pattern perception.

Topography of the corpus callosum in the cat

Discrete application of horseradish peroxidase to the corpus callosum in cats produced labeled neurons within a dorsoventrally elongated cortical territory. The rostrocaudal position of the territory corresponded with that of the applications. Callosal fibers from the ventral half of the frontal cortex passed through the rostrum, and those from the ventral occipital and dorsal temporal cortex passed through the ventral splenium. These results indicate a sectorial topographical correspondence between the corpus callosum and the cortex.