An albino-like decussation error in the optic chiasm revealed by anomalous ocular dominance columns
We report a unique anomaly in the ocular dominance column pattern of a single, normally pigmented macaque monkey. The column pattern contained large monocular areas inserted between the normal columns and the dorsal V1 border. These monocular regions received transneuronal input from the contralateral eye, indicating that a small population of temporal ganglion cells erroneously decussated at the optic chiasm. Projection of the column pattern back onto the visual field showed that the monocular wedges represented a [similar]5-deg sector of ipsilateral field. This corresponded to the extent of naso-temporal overlap of ganglion cells in the normal retina, suggesting an error in axon guidance affecting cells close to the vertical midline of the retina. The consequences of the crossing error in this animal were threefold: it produced an anomalous monocular zone near the V1 border, the vertical meridian was not represented at the V1 border, and points near the vertical meridian were represented twice in the brain, once in each hemisphere.(Received May 10 2002)
(Accepted July 29 2002)
Key Words: Primary visual cortex; Cytochrome oxidase; Stereopsis; Axon guidance; Albino.
c1 Address correspondence and reprint requests to: Lawrence C. Sincich, Beckman Vision Center, University of California—San Francisco, 10 Koret Way, San Francisco, CA 94143-0730, USA. E-mail: email@example.com