Effects of cue type and overlap in context conditioning : the role of the hippocampus

Abstract

An environmental context can be represented as a collection of individual features, or as a conjunction of elements combined by relational associations formed within the hippocampus. Separating out different experiences and then retrieving the correct representation becomes more challenging when cue elements start to overlap or become degraded. I designed a series of highly ambiguous context discrimination tasks based on sensory features including olfaction, vision, and geometric shape. Normal rats were able to discriminate highly ambiguous contexts defined by olfactory cues, visual cues, and certain geometric shapes. Rats with hippocampal lesions were impaired in the olfactory and visual task, and showed enhanced performance on the geometric shape task. In a final experiment, I demonstrated that rats learned a novel pattern separation/completion task that utilized olfactory information as the retrieval cue. These studies suggest that in context discriminations, some features are more important than others and this influences hippocampal involvement.