Hippocampal-entorhinal codes for space, time and cognition
How do we remember important events? Focusing on episodic memory, I explored the idea that coding principles discovered in spatial navigation research are shared across cognitive domains. The hippocampal-entorhinal region might support our memory through the mapping of cognitive spaces; allowing us to remember where and when events occurred. Cognitive maps stored in memory can guide behavior through the simulation of possible future trajectories. Combining human imagination with representational similarity analysis of multi-voxel patterns, I show that compass-like representations in the parahippocampal gyrus and grid-like hexadirectional representations in the entorhinal cortex contribute to mental simulation. The regular firing patterns of grid cells in the entorhinal cortex supposedly provide a metric for cognitive maps. Hence, grid pattern distortions might affect cognitive functions. Employing immersive virtual reality technology, I demonstrate that human spatial memory is distorted in a trapezoidal environment — mirroring distortions of grid-cell firing patterns in navigating rodents. These mnemonic distortions persisted in memory outside of the trapezoidal environment. Beyond space, time constitutes a second fundamental dimension for episodic memories. I show that the anterior-lateral entorhinal cortex maps the temporal structure of a learned event sequence and that this temporal map relates to memory recall. Combining findings from rodent electrophysiology, cognitive neuroscience and a theory from cognitive science, I describe a theoretical framework for how the hippocampal-entorhinal region might support memory and other cognitive functions through the mapping of cognitive spaces.