Working memory is a mechanism for short-term active storage of information and for processing stored information. Although evidence for temporary storage mechanisms of information has been accumulated, little is known about neuronal mechanisms for processing information. To understand how information is processed in the nervous system, we first need to know what information single-neuron activity represents, then examine how represented information by single-neuron activities changes along the temporal sequence of the trial. We used two kinds of culomotor delayed-response (ODR) tasks and examined what information prefrontal single-neuron activity represents. We found that all cue-period activity encoded cue positions. However, among neurons, which exhibited delay-period activity, 86% encoded cue positions, while 13% encoded saccade directions. In addition, among neurons exhibiting oculomotor activity, 58% encoded saccade directions, while 35% encoded cue positions. To visualize temporal patterns of changes of information represented by a population of prefrontal neurons, we analyzed single-neuron activities using a population vector analysis. As a result, we found that information represented by a population of PFC neurons changes gradually during the delay period from information for visual cue to that for saccade. (C) 2003 Published by Elsevier B.V.