Neuronal circuitry related to working memory in the prefrontal cortex

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To investigate how information for multiple spatial positions is retained by prefrontal neurons, neuron activity was recorded from the prefrontal cortex of two monkeys while they performed two tasks ; in the delayd sequential reaching task, monkeys were required to retain two cue locations and the order of their presentation, while in the delayd reaching task, monkeys were required to retain only one location. Among 138 task-related neurons, 72 showed statistically significant delay-period activity. By comparing the activity across both tasks, the delay-period activity were classified into four groups. 19 neurons exhibited delay-period activity only when the visual cue was presented at a particular position ; in 6 neurons, the cue position was important for eliciting the activity, whereas 13 exhibited the activity only when the visual cues were presented at a particular position in a particular order. 39 neurons exhibited delay-period activity only when the visual cues were presented a … More t two particular positions ; 13 exhibited this activity regardless of the temporal order of cue presentation, whereas 26 exhibited the activity only when the visual cues were presented in a particular temporal order. The remaining 14 exhibited either non-differential activity or miscellaneous activity. The present experiment shows that the new class of delay-period activity emerged to retain multiple positions and the temporal order of cue presentation ; pair-dependent and temporal order-dependent activity. Pair-dependent delay-period activity could be a mechanism for simultaneously retaining multiple bits of spatial information and for effectively interconnecting these information by a single neuron. The presence of the activity with temporal order-dependency suggests that the periprincipal area plays a role in planning and executing sequential behaviors and that retaining both the positions and the temporal order of the presentation could be an another effective strategy for retaining and interconnecting multiple bits of information. Less