| Research Abstract |
Primate temporal lobe plays an indispensable role in the cognitive memory functions. It contains two phylogenetically different structures, the temporal neocortex in the parahippocampal cortex (area TE according to von Bonin ＆ Bailey) and the hippocampus. We has been proposing a hypothesis of the primate visual memory system in which the area TE is considered as the memory storehouse. To test this hypothesis, single-unit activities of the temporal cortical neurons were examined while the monkeys were performing a visual memory task (delayed matching-to-sample task, DMS). We found shape-selective neurons that exhibited sustained activity during the delay period of the DMS task. The activity was highly selective for the pictorial information to be memorized and was independent of the physical attributes such as size, orientation, color or position of the object, suggesting that the delay activity represents the short-term memory of the categorized percept of a picture. Moreover, the selectivity of these delay discharges developed through repeated trials of the DMS task. Computer-generated artificial patterns were used as the stimuli to be memorized. The few patterns for which a neuron was conjointly selective were frequently related to each other through stimulus-stimulus association imposed during the course of training. Thus, the selectivity acquired by these cells is suggested to represent the associative long-term memory of pictures. These observations not only support the proposed hypothesis but also give more concrete, vivid shape to the neural representation of the presumed memory storehouse.
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