Error correction in the hippocampal-medial-entorhinal cognitive map
Error correction in the hippocampal-medial-entorhinal cognitive map Tereza Vargová Summary Spatial navigation is a crucial skill for survival. The hippocampal-medial-entorhinal network contains multiple classes of spatially modulated cells, namely place cells, grid cells, border cells, and head direction cells. These cell types are thought to create, maintain, and update the cognitive map of the brain. However, they are also known to accumulate error with distance travelled and recent studies have shown that environmental clues have a complex influence on their firing patterns. In this thesis, I investigate the effect of environmental landmarks on error correction in spatially modulated cells during one dimensional navigation in a virtual reality environment, using in vivo chronic multi-tetrode recordings from mouse hippocampus and medial entorhinal cortex. My experimental data shows that increasing the number of available visual cues resulted in an increase in the number of firing fields, decrease in the field size and variability, and increase in the cells’ peak firing rate while mean firing rate remained unchanged. Importantly, cell type-specific preferences for field position in relation to cue location were observed. Average drift in field position during repeated laps in a trial decreased significantly with increasing number of cues. Decrease in this drift was significantly stronger in fields located closer to the visual cues. The precision with which cells corrected their drift also significantly increased with increasing number of cues. The presence of a non-visually cued fixed reward location decreased drift, suggesting that error in spatial cell firing can be modulated by non-visual cues, too. Increasing the spatial information content of the presented visual cues further increased all these stabilizing effects. The above changes resulted in the animal’s increased precision in anticipating the reward location. Overall, my results show that increasing the number and information content of cues in the environment helps correct error in the firing of spatial cells by stabilizing their firing fields and increasing their spatial resolution. These changes lead to improved performance in a navigation task.
hippocampus, cognitive map, error correction, entorhinal cortex, grid cells, place cells, drift, navigation, virtual reality
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