Event related potentials (ERPs) will be recorded in nonhuman primates while they are engaged in visual memory tasks. The primary focus will be on determining the morphology, topography and functional properties of the long wave potentials, which occur at or near 300 msec (P300). P300 potentials have been used as indices of cognitive activity in humans. Our goal is to develop an animal model of visual memory that may be eventually used to study the neural structures involved in generating ERPs. Two visual memory paradigms will be used, the serial probe recognition (SPR) and delayed matching-to-successive samples (DMTSS) tasks. In the SPR task, a list of items (pictures of objects or scenes) is shown to a subject. Then a test item called a probe is presented and the subject must respond in one way if the probe item had occurred in the list and in another way if it was not a member of the list. Humans and monkeys show similar performance in the SPR task; our studies will determine whether or not the two species' ERPs will reveal similar memorial processes. Recently, ERPs recorded form Alzheimer's patients in the SPR task have shown reduction of these potentials. If the ERPs of monkeys and humans are similar, then we will have an ideal model of information processing to address questions that can not be answered with human subjects (e.g., drug, ablation, brain trauma effects). In the DMTSS task, the monkey is trained to match the order of presentation of two successive samples. Thus, this task requires both item and order memory. We are interested in the DMTSS task as an animal model for the assessment of sequencing. Patients following head trauma typically display disorders of organization. Whether the disorder involves primarily memory processes is difficult to determine at this time. Animal models, which show functional correspondences with human cognitive functioning, will allow detailed study of the structures and processes involved in memory.