FUNCTIONAL MODULES IN THE MACAQUE INFEROTEMPORAL CORTEX

     The anterior part of the macaque inferotemporal cortex (IT) represents a higher stage of the brain pathway involved in object vision.  In order to investigate how object images are processed in this area, we studied the spatial distribution of those anterior IT neurons which have related stimulus selectivity, in anesthetized and immobilized monkeys (Macaca fuscata).
     We compared the stimulus selectivites of multiple neurons which were recorded simultaneously with a single electrode and were separated with 2 window disicriminators.  The stimulus features critical for activation of one cell were analysed by a procedure involving step-by-step simplification of the images of effective objects with a computer graphics system.  After the optimal feature was determined for that cell, we prepared a set of stimuli including those similar to the optimal one, and examined the other units with this set.  Adjacent cells in the anterior IT responded to similar stimuli.  The exact optimal feature or the tuning width, however, often differed slightly between adjacent cells.
     We then assessed the spatial extent of clustering of neurons with similar selectivity by inserting electrodes tangentially and at right angles to the cortical surface.  In penetrations directed normal to the cortical surface, we obtained cells with related selectivity over a distance of 0.6-1.4mm, suggesting that cells with similar stimulus preferences cluster across cortical layers.  In tangentially directed penetrations, cells with related selectivity were grouped within 0.2-0.5mm.
     We suggest that the anterior IT consists of modules, each containing cells with related, but often not identical, stimulus selectivity.


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