Population-vector analysis by primate prefrontal neuron activities

The population-vector analysis was applied to visualize neuronal processes of sensory-to-motor transformation in the prefrontal cortex while two monkeys performed two types of oculomotor delayed-response (ODR) tasks. In a standard ODR task, monkeys were required to make a quick eye movement to where the visual cue had been presented 3 s before, whereas in R-ODR task, monkeys were required to make an eye movement 90° clockwise to the direction that the visual cue had been presented. In both tasks, directions of population vectors calculated from cue- and response-period activity were almost the same as cue directions and saccade directions, respectively, indicating that population vectors of cue- and response-period activity represent information of visual inputs and motor outputs, respectively. To visualize neuronal processes of information transformation, population vectors were calculated every 250 ms during a whole trial. In ODR task, population vectors were directed the same direction as the cue direction during the delay period. However, in R-ODR task, population vector rotated gradually from the direction similar to the cue direction to the saccade direction during the delay period. These results indicate that visual-to-motor transformation occurs during the delay period and that this process can be visualized by the population-vector analysis.