Hippocampal regulation of encoding and exploration under the influence of contextual reward and anxiety

Hippocampal researchers have recently turned their attention to the computations that may be implemented by the hippocampal circuit (e.g. pattern separation and pattern completion). This focus on the representational and information-processing capabilities of the hippocampus is likely to be important in resolving on-going debates regarding the nature of hippocampal contributions to perception, anxiety and exploration. A first aim of my research was to examine how context representations interact with reward to influence memory for embedded events. In my first experiment, I show that recollection for neutral objects is improved by sharing a context with other rewarding events. To further examine contextual influences on memory, I conducted a second experiment that examined the effect of contextual reward itself on object memory. Additionally, I manipulated the extent to which disambiguation should rely on hippocampal computations, by varying the perceptual similarity between the rewarding and neutral contexts. Improved object memory was only observed when the rewarding and neutral contexts were perceptually similar, and this contextual memory effect was further linked to co-activation of the hippocampal CA3/dentate gyrus and substantia nigra/ventral tegmental area. A second major aim of my work was to characterize hippocampal contributions to anxiety. In my third experiment, I combine a novel experiment with fMRI to show that hippocampal activation is associated with behavioural inhibition rather than exploratory risk assessment. This insight is important because a major theoretical perspective in the literature conflates these two psychological processes. In my final experiment, I employ this novel experimental paradigm to examine the effect of exploration on memory, and find that the propensity to explore (rather than the act of exploring per se) leads to better memory at subsequent recall.