Mnemonic Firing of Neurons in the Monkey Temporal Pole During a Visual Recognition Memory Task. Nakamura, Katsuki, and Kisou Kubota. Department of Behavioral and Brain Sciences, Primate Research Institute, Kyoto University, Inuyama, Aichi 484, Japan.
APStracts 2:0035N, 1995.
SUMMARY AND CONCLUSIONS
1. We examined single neuronal activity in the temporal pole of monkeys, including the anterior ventromedial temporal (VMT) cortex (the temporopolar cortex, area 36, area 35, and the entorhinal cortex) and the anterior inferotemporal (IT) cortex (area TE), during a visual recognition memory task. In the task, a trial began when the monkey pressed a lever. After a waiting period, a visual sample stimulus (S) was presented 1-4 times on a monitor with an inter-stimulus delay. Thereafter, a new stimulus (R) was presented. The monkeys were trained to remember S during the delay period and to release the lever in response to R. Colored photographs of natural objects were used as visual stimuli. 2. About 70% of the recorded neurons (225/311) responded to at least one of the Ss tested. Thirty percent of these neurons (68/225) continued to fire during the subsequent delay periods. In 75% of these neurons (51/68), the firing during the delay period strongly correlated with the response to S. 3. The discharge rate during the delay period did not correlate with the monkey's eye movements, pressing or releasing of the lever, or the reaction time. 4. If the monkey erroneously released the lever in response to S or during the delay period, the firing disappeared after the erroneous lever- release. If the monkey failed to release the lever in response to R, the firing persisted even after R was withdrawn. The discharge rate in incorrect trials was comparable to that in correct trials. The neurons were considered to fire for as long as the memory of S was necessary. 5. Firing persisted even when an achromatic version, or half (even a portion), of S was presented, indicating that the color, a particular portion, or the entire shape of S was not always necessary to elicit firing. 6. An S that elicited firing during the delay period invariably elicited a visual response. Neurons which fired during the delay period showed a higher stimulus selectivity than other visually responsive neurons in the anterior VMT cortex. Thus, neurons which fire during the delay period represent a subgroup of visually responsive neurons which are selectively tuned to a certain stimulus. 7. More neurons fired during the delay period in the anterior VMT cortex than in the anterior IT cortex. 8. We conclude that firing during the delay period by neurons in the temporal pole reflects the short-term storage of visual information regarding a particular S. 

Received 22 February 1994; accepted in final form 27 February 1995.
APS Manuscript Number J90-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  3 April 1995.