The maps in our minds

ScienceDaily reports research from the Norwegian University of Science and Technology on the mapping facility of the brain. (here) The research was done on rats but the investigators believe it applies to humans because the hippocampus and entorhinal cortex (site of spatial mapping) are the oldest and best conserved areas, across evolution, of all the forebrain structures.

The rat brain mapping system thus consists of a series of small maps, not just a single large one. … A recently discovered cell type, border cells, which are active along certain walls in a given environment, may shed light on this question. Border cells describe the limits of how an environment ends and another begins.

The same report includes research by K. Kjelstrup and how the multiple maps are used.

“We need maps of varying resolution, some small detailed maps, and other, larger rougher maps … and the brain sorts these very systematically.”…The maps are stored as extremely thin cards in a deck in the hippocampus, the area that is regarded as the brain’s memory focal point. The deck is sorted by rank, so that the fine-grained detail maps located at the top, with the biggest, most coarsely drawn maps the further down in the deck that you come.

So it appears that in its simplest (probably too simple) visualization the mapping facility with its four types of cell (place, grid, direction, border) works in the following way:

- We recognize which map we are in from the sensory match with a place using place cells and that activates a memory map in the hippocampus

- This current map is laid out on the grid cell array in the entorhinal cortex. The grid and place cells indicating where we are on the map and the direction cells indicating our heading (in orientation or movement). Reaching border cells indicates the need for a new map.

- A new map is fetched from the hippocampus as indicated by the heading and/or the place information.

- New maps would be formed (as memories) and old ones updated as needed.

What aspects of all this would enter consciousness? We are aware of where we are usually and of our heading. When we do not, we have the fringe feeling of being lost or a fringe feeling of being in an entirely new place, or both. But although usually we have this sense of where we are, it is usually not the focus of attention – in awareness but not in focus.

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