Contextual Learning In The Limbic Memory Circuit
Context plays a critical role in memory. Information obtained during learning gets bound to the context and the context itself can serve as a potent retrieval cue. It has been well known since the 1970's that the hippocampus (HP) plays a critical role in processing contextual information. Research has shown that learning two lists of items in two different contexts facilitates learning compared to learning both in one context, and damage to the HP abolishes this advantage. Electrophysiology studies have indicated the HP forms contextual representations of an environment quickly and that the representation remains stable thereafter. The HP also encodes non-spatial information such as events, cues and time. The HP and AT are strongly interconnected and it is well known now that damage to the anterior thalamic nuclei (AT) produces severe memory deficits in multiple memory domains similar that following damage to the HP. However, it is not known whether the AT is critically involved in contextual memory processes like the HP. The first chapter evaluated whether the AT is involved in contextual learning of a context dependent odor discrimination task. The results showed that like the HP, damage to the AT abolishes the contextual advantage of learning two sets of odor discrimination problems in separate contexts. The second chapter evaluated how neuronal representations in the HP change when learning two contexts concurrently. While studies have evaluated how neuronal representations change between context exposures, none have evaluated the concurrent development of two contexts. The results showed that several exposures to the same context are required to form a stable HP representation of the two contexts. The final iii chapter evaluated what event responses arise when learning the same task as chapter one and how these event representations change with learning. The results show that as learning progressed, event responses decreased in number. This decrease may be due to the responses becoming part of a general trial sequence indicating the stabilization of the representation as learning progressed. The current dissertation provides new evidence for how the memory circuit encodes contextual memory. iv
Context; Hippocampus; elctrophysiology
Smith, David M.
Regan, Elizabeth; Devoogd, Timothy John; Cutting, James Eric
Ph.D. of Psychology
Doctor of Philosophy
dissertation or thesis