Cortical connections of subdivisions of inferior temporal cortex in squirrel monkeys

Patterns of cortical connections and architectonics were used to determine subdivisions of inferior temporal (IT) cortex of squirrel monkeys. Single or multiple injections of the tracers wheat germ agglutinin‐horseradish peroxidase, Fast Blue, Diamidino Yellow, Fluoro‐Gold, and 3 H‐amino acids were placed into IT cortex. Most injections were placed in caudal IT cortex in the region previously shown to receive input from the caudal subdivision of the Dorsolateral Area, DL c ; additional injections were placed in more rostral IT cortex. The results indicate the presence of two major regions: a caudal region, IT C , and a rostral region, IT R . An intermediate region of cortex along the IT c −IT R border that displays some connections of IT c and some connections of IT R may be another area. IT c contains a more myelinated dorsal area, ITCd, and a larger ventral area, ITCv. Both ITCd and ITCv receive a major projection from DL C ; additional input from DL R , MT, and VII; and send strong projections to IT R , the lateral bank of the superior temporal sulcus, and dorsolateral prefrontal cortex. Only ITCd has strong connections with DL R and cortex in the depths of the superior temporal sulcus, and only ITCv has connections with lateral orbital cortex. The overall pattern of connections between IT C and DL C suggests that IT C has a crude topographic organization, with dorsal cortex representing the lower field and ventral cortex representing the upper field. IT R differs from IT C by receiving little if any input from DL C ; projecting to inferior temporal polar cortex, the rostral Sylvian fissure, and medial orbital cortex; and having a less distinct layer IV. Comparison of subdivisions of inferior temporal cortex defined in the present study in squirrel monkeys and those reported in other primates suggests that IT C of squirrel monkeys may correspond to area TEO of macaque monkeys.