The major objective of this proposal is to understand how different olfactory recipient areas of the hamster brain participate in learning and storing odor information about other individual hamsters. This will be done by analyzing the coding properties of single neurons and ensembles of neurons in olfactory cortex, entorhinal cortex and hippocampus while hamsters perform two types of individual discrimination recognition tasks that differ in their processing demands. The first test is a basic habituation discrimination task in which hamsters are repeatedly presented with odors from one individual hamster and are then presented with another animal's odor. Hamsters form and maintain some memory of different individuals' odors over long periods of time as evidenced by habituation of investigation to one odor and increased investigation of the new individual's odor. The second task is a variation on this paradigm in which hamsters are allowed to interact with two individuals (A & B) for several days and are then habituated to one particular odor from A and then tested with another particular odor from A. Behaviorally, hamsters generalize their habituation to the second odor only if they have previously interacted with that animal, indicating that hamsters associate the two perceptually distinctive odors with each other and that they come to represent the individual hamster. This latter test provides an opportunity to test the hypothesis that the hippocampal system is involved in the formation of declarative (conscious, relational and flexible) memories, but not procedural (unconscious, inflexible, and limited) memories by predicting that only hippocampal neurons will code this odor-odor relationship. In contrast, social odor memories formed in the first task are non-relational and are therefore not predicted to require hippocampal coding but will be represented in olfactory and entorhinal cortex activity. This proposal is part of a broader research program that uses rodent species as experimental models of human amnesia with the explicit intent of characterizing the neural structures involved in human memory formation.
