Learning produces long-term changes in behavior, physiology, and gene expression. Although this principle is now well-documented across the animal kingdom, fundamental aspects of learning and memory remain unclear: 1) how physiological and genetic changes supporting long-term memory are integrated across a neural circuit. 2) if forgetting represents the decay of long-term memory processes or an active erasure process, and 3) how individual differences in memory acquisition and retention arise. To address these fundamental issues in learning and memory, we propose a simple set of experiments using long-term habituation of the Aplysia tail-elicited siphon-withdrawal reflex (T-SWR). Groups of animals will be exposed to long-term habituation training (5 blocks of 30 stimuli applied to one side of the tail, 30s ISI, 90 min between blocks). This training produces a long-lasting and unilateral decrease in T-SWR behavior. To determine the physiological correlates of LTH, trained animals will be anesthetized and reduced to a siphon+tail preparation, enabling physiological recordings from the T-SWR circuit during ongoing behavior. By comparing tail-evoked neural activity from the trained and untrained side of each animal, it will be possible to identify sites of long- term neural plasticity elicited by LTH training. After physiological recordings, neurons from trained and untrained sides of each layer of the T-SWR circuit will be physically isolated. To determine the molecular correlates of LTH, RNA from harvested cells will be extracted, reverse-transcribed, and profiled using microarrays. By repeating this same procedure with animals harvested 1 and 7 days after training, it will be possible to determine physiological and genetic correlates of a memory expression (1 day) and decay (7 days). In addition, within group analyses will enable identification of physiological and transcriptional factors that predict the considerable variability evident in the acquisition and decay of long-term habituation. Finally, LTH correlates identified with this approach will be experimentally manipulated to determine their casual role in the expression and decay of LTH memory. This project provides a tractable means to gain fundamental insight into the mechanisms of long-term memory in an experimental context that offers excellent opportunities for undergraduate involvement.
This project will explore the genetic and neural changes that mediate long-term memory for habituation, a simple form of memory that is shared across the entire animal kingdom. By studying the mechanisms of habituation in a simple model organism (Aplysia californica), it will be possible to gain fundamental insight into the processes by memories are stored and subsequently decay. Results may have implications not only for the treatment of memory disorders, but also for a variety of attentional processes thought to depend on habituation.
