S128

HORIZONTAL CLUSTERED CONNECTIONS IN THE MACAQUE INFEROTEMPORAL CORTEX.

EHIRO FUJITA,t KS. SALEEM,.t AND HISAYUKI OHMA, Labomries for ‘Neural Information

Processing and 2NwI Svstems. Frontier Rercb Program. RIKEN. Wako. &&BR~ 351-01. a

Clustered arborizations of horizontal axons have been reported in the primary and secondary visual, primary auditory and

motor cortices in cats and monkeys. This study examined whether similar structure is present in a higher visual cortical area,

the inferotemporal cortex (IT) of the monkey. Biocytin (4%) was injected iontophoretically (7 pA x 25 min, 7 set on-7 set

off) into cytoarchitectonic areas TBO and TE of IT in 2 monkeys (Mucaca~ca~u). The IT was cut tangentially and sections

were treated with the avidin-biotin complex method. Detailed structure of labeled fibers, terminals and cells was visualized as

in best Golgi-impregnated materials. Both TEO and TB injections resulted in patchy distributions of anterogradely labeled

terminals within respective areas. A single injection produced up to 8 patches, 0.3-0.8 mm in diameter and 0.8-3.6 mm from

the center of the injection site. Some injections retrogradely labeled many pyramidal cells. These cells tended to be clustered

in areas where labeled fibers and terminals were densely distributed. We conclude that intrinsic horizontal axons arborise in a

clustered manner in IT. This organization may explain physiological observations that cells with similar stimulus selectivities

are found in 2 or 3 separate groups along tangential electrode penetrations in area TE (Fujita, Cheng and Tanaka, 1991).

DIFFERENT CELL POPULATIONS IN AREA V4 PROJECT TO POSTERIOR AND ANTERIOR

INFEROTEMPORAL CORTEX IN THE MACAQUE: A DOUBLE LABEL TRACER STUDY.

M. ICmRO FUJITA AND KEIJI TANAKA, Laboratory for Neural Information Processing,

Frontier Research Program, RIKEN, Wako, Saitama 351-01, Japan.

The inferotemporal cortex of the macaque is divided into areas TEO and TB. Both TBO and the posterior part of TE (TBp)

receive affemnt inputs from area V4. In this study we made simultaneous injections of 2 different retrograde fluorescent tracers

(fast blue and diamidino yellow) into TBO and TEp in 4 monkeys (Mucacu~caru) and compared the distribution of TBO- and

TBp- projecting cells in V4. TBO injections led to an extensive and continuous labeling in the part of V4 that corresponds to

central representation in the ventral part of the prelunate gyrus and to a sparse labeling in the part of V4 representing peripheral

visual fields in the dorsal prelunate gyrus. Labeling in V4 also extended ventrally across both banks of the inferior occipital

sulcus. TBp injections labeled cells in a similar part of central V4, as TEO injections did. TEp injections, however, resulted in

a patchy distribution, in contrast to the continuous labeling after TBO injections. Cells labeled with different dyes were

intermingled with each other in the patches, and only a small number of cells (0.5%) were double labeled. We conclude that

different cell populations in V4 project to TBO and TBp, although two populations are intermingled in the same area.

RESPONSE PROPERTIES OF MONKEY'S INFERIOR TEMPORAL NEURONS TO ONE AND TWO VISUAL STIMULI DURING MATCHING TASK. TAKAYUKI SATO, AND TAKESHI KAWAMURA, Department of Behavioral Physiology, Tokyo Metropolitan Institute for the rIeuroscience, 2-G Plusashidai Fuchu-city, Tokyo 183, Japan

Macaque monkeys were required to determine if two visual stimuli presented at separate locations were the same or different. Two stinuli of paired patterns or color spots were presented simultaneously, or in the other paradigm, one stimulus was delayed by 500ms and both stimuli were then presented. r1euron's selectivity between paired stimuli in the single stimulation remained similar for double stimulation of the same stimulus, while the selectivity improved slightly during the double stimulation. During the double stimulation, SOIW neurons showed stronger response to different stimuli than to the same stimuli, and this effect was more prominent in the selectively responsive neurons, though the different stimuli were consisted of optimal and non-optimal stimuli.