Recent research in the neurobiology of primate memory has called into question the role of the hippocampal formation in memory processing. Instead the (ento- and peri-) rhinal cortical areas seem to be the neural areas crucial for memory. Because monkeys are typically tested in single-item recognition memory tasks which human amnesiacs with hippocampal damage can solve, a monkey task similar to the amnesic patients' memory tasks needed to be developed. We have developed such a task; it is a list memory task in which monkeys can perform well. This task provides serial position primacy and recency effects (good memory for the first and last items, respectively) which reflect separate underlying memory processes. Three groups of 6 monkeys each will receive either bilateral excitotoxic lesions of the hippocampal formation, bilateral aspiration lesions of the rhinal cortex, or none (controls). They will be tested pre- and post-surgically in the list memory task in which retention interval and interference will be parametrically manipulated over a substantial range. These manipulations have been shown to produce significant and definable changes in primacy and recency effects of the serial position function. Performance of the operated monkeys will be compared to that of control animals and their own pre-surgical performance in the list-memory task. This project is designed to further our understanding of the neural basis of memory processing and may provide insights into the neural substrates underlying human cognitive processes and deficits associated with aging and disease states, such as Alzheimer's and Parkinson's.
