Kaplan, RSM; (2013) Brain oscillations and novelty processing in human spatial memory. Doctoral thesis (PhD), UCL (University College London).

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Abstract

Hippocampal activity in rodent model systems is commonly associated with movement and exploratory behaviour, while human hippocampal research has traditionally focused on mnemonic function. I attempted to bridge this gap with a set of experiments where human participants performed an interactive virtual navigation paradigm that resembled rodent spatial exploration tasks, in conjunction with neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). I then used this interactive paradigm to examine the oscillatory correlates of memory, novelty and the behavioural relevance of the default mode network. The first experiment used MEG and fMRI to examine whether the movement-related theta rhythm (4-8 Hz) recorded from the rodent hippocampus has a measurable human analog. I found that the human hippocampal theta rhythm supports memory, and may coordinate exploratory movements in the service of self-directed learning. In further analyses in Experiment 2, during cued spatial memory retrieval, I observed that medial prefrontal cortex theta phase couples with ongoing theta oscillations in the right anterior medial temporal lobe and with neocortical gamma (65-85 Hz) amplitude. In Experiment 3, with fMRI I investigated the effect of environmental novelty versus object novelty during the navigation task and found that hippocampal activity is modulated only by environmental novelty, while the fusiform gyrus/posterior parahippocampal cortex responded to object novelty. Finally, in Experiment 4 using 3T and high-field 7T fMRI, I investigated endogenous (task-free) periods that flanked different stages of a spatial navigation paradigm to determine how endogenous slow oscillations in the default mode network correlate with subsequent spatial memory performance and found mixed evidence that default mode network activity predicts individual performance. Finally, I discuss my results in the context of recent findings in spatial memory and novelty processing, and consider the relationship between the human hippocampus and rodent model systems.

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