Psychophisiological study of the working memory in relation to parallel processing

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The prefrontal cortex has important functions in organizig goal-directed, purposive hehavior.Working memory is the memory process of retaining the information "on-line" while that information is necessary for the correct performance.During the delayd response task, prefrontal neurons show activity changes during the delay period ("delay neurons") , some of them showing spatial specificity depending on the cue position.This study was conducted whether prefrontal neurons are involved in retaining more than two different kinds of information in parallel.Three monkeys were trained on three different typse of delayd response tasks with several kinds of food and liquid reward ; (1) Direct method food reward, (2) Indirect method food reward, and (3) Indirect method liquid reward.Type of task and kind of reward were changed usually in a block of 50 trials.The results of the experiment are summarized as follows.(1) About 2/3 of delay neurons examined showed differential activity depending on whether it was a right or left trial, and thus had spatial specificity.(2) About half of delay neurons showed differential activity depending on the difference of the reward, and thus had reward dependency.(3) About 80% of delay neurons showed differential activity depending on the difference of the type of the task, and thus had task dependency.(4) Substantial proportion of delay neurons with spatial specificity had reward dependency and/or task dependency as well, participating two or three different kinds of working memory.(5)These prefrontal neurons which are involved in retaining several kinds of information in parallel, are considered to be the basis of the goal-directed behavior where parallel processing is required.