Neural mechanisms of spatial navigation and memory

Jonathan F. Miller

doi:10.17918/etd-7189

The ability to navigate our environment is a vital skill for numerous species, including humans. How does the brain encode external space to allow for accurate navigation? Moreover, as we move through the world, how do we keep track of where specific events occur? Based on decades of research in rodents, we know that the hippocampus contains place cells that code for particular locations in the environment, and based on decades of work in humans, we know that the hippocampus is crucial for episodic memory function. The goal of this thesis is to study how the human brain simultaneously supports spatial navigation and episodic memory by analyzing intracranially recorded neural activity from participants performing virtual spatial memory tasks. In my first study, I investigated whether the neural representation of space formed by the place cell population code in the medial temporal lobe (MTL) becomes integrated with a broader memory signal. I found that place cells in human MTL act as a mechanism for memories to become linked to the location where they occurred, suggesting that the neural system underlying spatial navigation and the neural system underlying memory function are not as distinct as once thought. In my next study, I investigated whether anatomical subregions of the human MTL, specifically the entorhinal cortex (EC) and the hippocampus, differ in the type of spatial information that they are selective to, which has been shown to be true in rodents. I discovered a new type of cell in the human EC called path equivalent cells that provides a metric of distance relative to an environment's geometry, unlike hippocampal place cells that only fire at specific locations. This finding helps to bring our understanding of how space is represented in the human brain closer to our more in depth understanding of spatial representations in the rodent brain. In my final study, I investigated how oscillatory activity in the human hippocampus is modulated by movement through the environment. In rodents, the theta oscillation (4-8 Hz) is closely linked to voluntary movement through space and is an integral component for many rodent derived theories of MTL function. I found that functionally analogous signals in human hippocampus appeared at lower frequencies than in rodents, suggesting that these theories may require modification before they can be broadly applied to other species. Taken together, my work helps to reconcile how the MTL supports both spatial navigation and episodic memory function, as well as bridging the gap between the large literature describing the neural representation of space in the rodent brain and the comparatively less well understood mechanisms in the human brain.

Neural mechanisms of spatial navigation and memory

Files and links (1)

Abstract

Metrics

Details

Neural mechanisms of spatial navigation and memory

Files and links (1)

Abstract

Metrics

Details

Drexel University Social media