The vibrant city of London.
Millions of people travel daily through its busy streets. To navigate well, we create mental maps of the city that help us find our way.
But how are these maps represented in the brain and how do we navigate between and connect to different places in our mind in?
This video will take a closer look at how our brain understands our location in space.
Most experimental research and spatial navigation and memory is done in rats. Through implants in their brains,
we can record the activity of a single cell. In the brain there are four important
cell types that encode location and direction: place cells,
grid cells, head direction cells and border cells. All of these cells are found in or around the hippocampus, an
important brain structure for memory.
Place cells are found in the hippocampus. They are only active when the animal is in one specific location in space.
Grid cells are found in the cortex surrounding the hippocampus.
They fire at multiple locations in space and this forms a neat pattern telling the animal how far it's traveled.
Head Direction cells only fire when the animal is facing a certain direction, and border cells only fire at the border of a room.
All of these cells also communicate with each other. Although
we still don't fully understand
how memory works, it is believed that the patterns of activity and
communication between these cells is stored while learning or exploring and then these same patterns are repeated at later times to give the brain an
idea of where in space you are and where you need to go.
This shows the activity of a single grid cell. You can see how as the
animal walks through the room, the grid cell firing form a strong pattern.
Recently, research has shown how these patterns can change to help the brain make better mental maps of space.
I want to see researcher Francis carpenter from the UCL cell biology lab to find out more about this research.
So we tested this idea that grid cells do actually act as a ruler for space by
recording from rats while they explored an environment which took the sensory inputs to grid cells
in conflict with
the self motion inputs, which tell the rest of the brain how fast an animal was moving, its velocity.
So the environment had two boxes that were
Essentially identical. So they look at the same, smell the same. So when you drop the rat in one or the other
the rats can't tell which box it was in.
But they're also connected by a corridor, so that if
the animal ran from one box to the other via the corridor, it could tell that obviously the boxes weren't the same, there can't be identical boxes.
What we found was that at the beginning experiments, the grid cells had same firing pattern in both, but as the
rat gets more experience with environment and it runs around between the box more often,
the pattern forms a single, continuous, and global pattern that spans the two boxes.
So grid cells change their firing patterns to connect to places that are next to each other.
But what can this tell about human navigation? So we know humans have place cells and grid cells,
so the analogy that we use to explain the result or what we think might happen in humans is that
when you move to a new city,
say when you come to London for the first time, that you might get separate maps or separate representations in your brain for different areas.
But if you then walked between them just like the
rats walk between the two boxes on the corridor in our experiment, then your brain can work out how these two
separate maps relate to one another. It can merge them together into a single representation,
which you can then use to navigate between these two areas. So the two maps come effectively to form a single one.
Now you know how grid cells represent space in the brain.
Hopefully this helps you understand a little bit more about how we form a sense of where we are in space, and where we're going.