Neuronal activity in posterior parietal area 7a during the delay periods of a spatial memory task.

1. Neuronal activity was recorded from area 7a of monkeys performing a delayed match-to-sample task requiring release of a behavioral key when a visual stimulus appeared at a remembered spatial location. 2. Activity in the delay periods was significantly elevated in 28% of 405 neurons studied and could be classified as either sustained or anticipatory in nature. 3. Sustained activity was characterized by maintained or slowly decreasing discharge rates that were typically greater when the preceding stimulus was at a location that evoked a strong response. Sustained activity was terminated when a subsequent stimulus appeared at another location. 4. Anticipatory activity was characterized by accelerating discharge rates that were ordinarily greater after a stimulus at a location that evoked a weak response. Anticipatory activity was often associated with facilitated responses to the next stimulus. 5. These data demonstrate that a population of neurons in area 7a is active during the delay periods of a spatial memory task that does not require a behavioral response directed toward the location of the stimulus. This activity could represent a short-term memory trace for the spatial location of the preceding stimulus.