MATCHING PATTERNS OF ACTIVITY IN PRIMATE PREFRONTAL AREA 8A AND PARIETAL AREA 7IP NEURONS DURING A SPATIAL WORKING-MEMORY TASK

Single-unit recording studies of posterior parietal neurons have indic ated a similarity of neuronal activation to that observed in the dorso lateral prefrontal cortex in relation to performance of delayed saccad e tasks. A key issue addressed in the present study is whether the dif ferent classes of neuronal activity observed in these tasks are encoun tered more frequently in one or the other area or otherwise exhibit re gion-specific properties. The present study is the first to directly c ompare these patterns of neuronal activity by alternately recording fr om parietal area 7ip and prefrontal area 8a, under the identical behav ioral conditions, within the same hemisphere of two monkeys performing an oculomotor delayed response task. The firing rate of 222 posterior parietal and 235 prefrontal neurons significantly changed during the cue, delay, and/or saccade periods of the task. Neuronal responses in the two areas could be distinguished only by subtle differences in the ir incidence and timing. Thus neurons responding to the cue appeared e arliest and were more frequent among the task-related neurons within p arietal cortex, whereas neurons exhibiting delay-period activity accou nted for a larger proportion of task-related neurons in prefrontal cor tex. Otherwise, the task-related neuronal activities were remarkably s imilar. Cue period activity in prefrontal and parietal cortex exhibite d comparable spatial tuning and temporal duration characteristics, tak ing the form of phasic, tonic, or combined phasic/tonic excitation in both cortical. populations. Neurons in both cortical areas exhibited s ustained activity during the delay period with nearly identical spatia l tuning. The various patterns of delay-period activity-tonic, increas ing or decreasing, alone or in combination with greater activation dur ing cue and/or saccade periods-likewise were distributed to both corti cal areas. Finally, similarities in the two populations extended to th e proportion and spatial tuning of presaccadic and postsaccadic neuron al activity occurring in relation to the memory-guided saccade. The pr esent findings support and extend evidence for a faithful duplication of receptive held properties and virtually every other dimension of ta sk-related activity observed when parietal and prefrontal cortex are r ecruited to a common task. This striking similarity attests to the pri ncipal that information shared by a prefrontal region and a sensory as sociation area with which it is connected is domain specific and not s ubject to hierarchical elaboration, as is evident at earlier stages of visuospatial processing.