Search for neuronal mechanisms related to thinking using flexible representation of various information on the nervous system

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We collected single-neuron activities from the prefrontal cortex while monkeys performed two spatial working memory tasks (ODR and R-ODR tasks) and constructed population vectors using all collected single-neuron activities. Population vectors constructed from cue- and response-period activity showed similar directions to the directions of the visual cues and the saccades in both tasks, indicating that these population vectors represent information regarding the direction of the visual cue and the direction of the saccade. Based on these results, we obtained population vectors during the 250 ms time window shifting every 50 ms during the delay period. In the ODR task, all population vectors were directed similar to the direction of the visual cue. However, in the R-ODR task, population vector rotated gradually during the delay period from the cue direction to the saccade direction. To understand neuronal mechanisms essential for the rotation of population vectors in the R-ODR task, we examined temporal patterns of two kinds of delay-period activity ; one encoding the cue location and the other encoding the saccade direction. We observed the rapid increase of delay-period activity encoding the saccade direction over the activity encoding the cue location, and found that the time course of this increase coincided with the initiation of rotation in population vectors in the R-ODR task. These results indicate that the information processed during spatial working memory tasks can be depicted as the temporal change of the direction in population vectors. These results also indicate that information processing during thinking corresponds to the gradual transition from a population of neuronal activities representing one kind of information to a population of neuronal activities representing other kind of information.