Is Spatial Map Shaped by Environmental Determinants?

Abstract

Humans and other animals form internal mental maps of the outer world in order to navigate. Hippocampal place cells and grid cells in MEC (medial entorhinal cortex) are the key components of this navigation system. However, the spatial map formed by place cells and grid cells is not rigid and is subject to change. Environmental structure, size, geometry, identity and the sensory cues present in the environment can have a strong influence over the spatial map. To study the effect of environmental factors on the spatial map, I first started with the study to determine if place cells behave differently in environments of different scales. Using a commercial wireless recording system and a novel position-tracking system developed in our lab, I could analyse spatial representation beyond artificially small arenas (≤1m2) and closer to ethologically appropriate spatial scales. In our experiments, arena sizes ranged from 1m2 to 16.5m2 which is much larger than the arena sizes employed in previous studies. We found that in large arenas (16.5m2), both dorsal and ventral hippocampal neurons become more spatially selective with less diffused fields and therefore might have a higher resolution representation. Finally, I quantified local distortions in grid maps using grid cell data from Hafting et al (2005). It has been empirically observed that grid patterns near the boundaries are more distorted as compared to in the center of the environment. And we wanted to determine if there are discernible trends in which grids distort. We found that grid patterns get compressed and distorted more near the boundaries of the environment than at the center. Hence, we conclude that environmental features like scale and boundaries do have an influence on the spatial map.