Soc. Neurosci. Abstr. 1997.10

TOPOGRAPHICAL RELATION BETWEEN HORIZONTAL PROJECTIONS FROM ADJACENT SITES IN THE MACAQUE INFERIOR TEMPORAL CORTEX: A DOUBLE ANTEROGRADE LABELING STUDY.

H. Tanigawa* and I. Fujita Dept. Cognitive Neurosci., Osaka Univ. Med. Sch., Suita, Osaka 565, Japan.

Intrinsic horizontal axons with patchy clusters of terminals in layers 2 and 3 are a basic anatomical feature shared by various cerebral cortices. The projection pattern of horizontal axons is an important factor in determination of the contribution of these axons to the overall functional architecture and information processing of a cortical area. Here we analyzed the topographic relationship between terminal clusters of horizontal axons originating from adjacent sites in the inferior temporal cortex (area TE) of the Japanese macaque monkey.
Two anterograde tracers, Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine, were focally administered into pairs of adjacent sites in layers 2 and 3 of area TE. The center-to-center distance between the paired injections was 0.5-1 mm, so that the two injection sites abutted each other. Each injection produced 5-15 clusters of terminals of labeled horizontal axons, which were in many cases distributed in an elongated manner in one direction across the cortex. The direction of elongation varied among injections. Most of the clusters produced by the two injections neither overlapped nor abutted each other, although in one or two of the clusters, projections from two injection sites overlapped partially or extensively.
The results show that adjacent sites in area TE are largely connected to spatially distinct sets of sites via horizontal axons. Given the extensive fiber connections between neighboring sites, we suggest that the organization revealed in this study increases the opportunity for interaction among columns which are selective for different visual object features, compared to an orgnization in which adjacent columns project to adjacent sites.(Supported by CREST.)

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