Visual Field Defects Associated With Damage To Area V2 And V3

The organization of area V2 described by functional topographic mapping indicates that area V2 adjoins area V1 along the representation of the vertical meridian in both dorsal and ventral cortex. The anterior border of V2 corresponds to the horizontal meridian, which is split such that the inferior horizontal meridian is located in dorsal cortex and the superior horizontal meridian is located in ventral extrastriate cortex. Area V3 adjoins V2 along the representation of the horizontal meridian in dorsal cortex, whereas area VP adjoins V2 along the representation of the

Figure 13 Location and functional mapping onto a surface-based map of human cerebral cortex. (A) Locations of visual areas V1, V2, V3, VP, V4v, and V3A on a surface-based atlas based on fMRI topographic mapping studies. (B) Locations of visual areas projected onto the surface visible man cerebral cortex. (C) Locations of functional activation loci from color-processing tasks (from Corbetta et al., 1990). (D) Motion-processing tasks. (E) Form-processing tasks. From Van Essen and Drury (1997).

Figure 13 Location and functional mapping onto a surface-based map of human cerebral cortex. (A) Locations of visual areas V1, V2, V3, VP, V4v, and V3A on a surface-based atlas based on fMRI topographic mapping studies. (B) Locations of visual areas projected onto the surface visible man cerebral cortex. (C) Locations of functional activation loci from color-processing tasks (from Corbetta et al., 1990). (D) Motion-processing tasks. (E) Form-processing tasks. From Van Essen and Drury (1997).

horizontal meridian in ventral cortex. This is the same topographic organization that has been reported for areas V2, V3, and VP in macaque monkey extrastriate visual cortex. Homonymous quadrantic visual field defects have been observed in two patients with astrocytomas of the extrastriate occipital cortex. Both patients had lower field quadrantanopias that extend up to, but not beyond, the horizontal meridian. Such quadrantanopias have been reported previously and were attributed to lesions of the calcarine cortex. The precise border of the visual field defect at the horizontal meridian is not likely to be caused by lesions of

V1 because the border between the lower and upper visual fields is congruent and a lesion is unlikely to precisely respect this border. Instead, quadrantic visual field defects are likely to represent injury to areas V2-V3 (VP) where the horizontal meridian is split into dorsal and ventral halves. Therefore, quad-rantic visual field loss may be a hallmark of lesions of early extrastriate cortical areas such as V2, VP (VP), or V4.

In another case, homonymous quadrantanopia was associated with cerebral diplopia (polyopia). This patient had an embolic infarction of the left inferior

Table III

Localization of Human V2 in Talairach Coordinates0

Table III

Localization of Human V2 in Talairach Coordinates0

V2 component

X plane

Y plane

Z plane

Right V2v

-7.7 + 4.2

-75.3+5.1

-7.5+4.9

Right V2d

-11.7 + 4.6

-91.5 + 4.3

2.7+8.6

Left V2v

7.8 + 4.0

-71.1 + 5.9

-3.3+5.9

Left V2d

8.2 + 3.5

-87.6+4.3

6.1+4.5

"Mean and standard deviation of the center of mass of dorsal and ventral V2 in the right and left hemispheres. These values are based on PET activations following topographic mapping of V2. V2 is more consistently localized in the x plane and least consistently localized in the z plane.

"Mean and standard deviation of the center of mass of dorsal and ventral V2 in the right and left hemispheres. These values are based on PET activations following topographic mapping of V2. V2 is more consistently localized in the x plane and least consistently localized in the z plane.

occipital lobe anterior to the primary visual cortex. Similar to the lesions described earlier, this lesion produced a superior visual field quadrantanopia that precisely respected the horizontal meridian. Thus, this lesion is likely to represent damage to ventral extra-striate areas V2 and/or VP. This patient had severe defecits in form and color recognition within the affected quadrant. In addition, the patient reported diplopic images within this quadrant. Although the mechanism of cerebral diplopia is not understood, it is possible that the loss or disruption of feedback signals from extrastriate areas V2 and/or VP to area V1 is responsible for this perceptual anomaly.

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