A Brief History of [Inner] Space:
Understanding the Brain’s GPS
Neural underpinnings of spatial navigation, with many illustrations and wordplays.
Summary: The brain contains mechanisms that allow its owner to keep track of their position and movement through spaces. One way of navigating is by counting the number of steps taken. Another way is by creating internal maps of the external world. There are various brain regions and cell types that support navigation.
Where are we?
How do we know it?
Where are we going?
When considering the kingdom of critters on the planet, it seems that if animals have both a healthy brain and the ability to move around, they are able to find their way from place to place. This is the case for bugs, lizards, birds, humans.
Yes, we may get lost sometimes, but when we are in a very familiar place, we know how to navigate it. When a place is unfamiliar, we can learn our way around or through it or use some kind of strategy to keep track of where we are.
Most of us know where we are just by looking around.
But if we’re blindfolded trying to hit a pinata, we can feel for it.
We can figure out where we are based on how many steps we took. That’s how ants navigate.
Navigation through Steps
In the desert, ants may have to travel for miles to find food and to return to their nest. But they are able to do it. Some scientists had a fun idea to figure out how ants are able to find their way between their source of food and their home.
Tall ants happened! The scientists put the ants on stilts and let them loose at their nests.
We would guess that the ants on stilts would get to their food faster. But that’s not what happened. Instead they walked twice as far as the place where their food was — past their food!
Next, short ants happened! The scientists tried cutting the ants’ legs to be half of their original length and found that the ants only walked half the distance that they should have to arrive at the food.
What a curious phenomenon! The ants must have some sort of internal pedometer that lets them know where they are! This is good enough to let most ants survive in the desert. But biologically, we humans cannot afford to go through the motions like that. Though a simple life of getting food and going home sounds pleasant sometimes, we have bigger plans for life! Our surroundings are changing all the time! What do we do?
It helps to have maps.
Navigation Through Maps
The brain serves as a cartographer for our bodies and the places we go. Let’s talk about our bodies first.
Back in the day, it used to be thought that the bumps and ridges on peoples’ skulls were related to their personality.
Maybe this portion (below, highlighted in pink) was thought to be linked to cautiousness, so if it was big, the person was assumed to have a lot of cautiousness about their character.
And this portion (below, highlighted in yellow) was linked to hope. The size of it was thought to determine how hopeful people were.
Though phrenology is a pseudoscience. Not an actual science.
An idea that came from phrenology was the finding that the brain does have mapping to the body. Not based on ridges on the skull, but based on the brain itself. Here is a sensory homunculus.
The part of the brain’s sensory cortex with the hand illustrated over it interprets information coming from the hands, the part with the tongue beside it interprets information coming from the tongue. If more of the brain’s space is given to a body part, that means that area will be more sensitive. This is why we are able to read braille with our hands, but not with our toes.
If we use electricity to zap the part of the brain that controls the feeling in our nose, then we would feel something in our nose.
The homunculus would explain how the brain maps our bodies, but what about how the brain maps where we are in relation to our environments?
The Discovery of Place Cells by John O’Keefe
In the early 70’s, a neuroscientist named John O’Keefe was having his rats forage for chocolates in an arena.
O’Keefe recorded electrical activity from the hippocampus, which is a part of the brain that is needed to make new memories.
The rats would wander all around the arena in search of chocolate, taking breaks at times, grooming themselves, sniffing around.
O’Keefe noticed that there were some neurons in the hippocampus that would become excited when the rat was in a certain spot in the arena. They would be excited there, whether there was chocolate there or not, whether the rat was grooming or not, whether the rat was walking through it or just sitting there.
What a pain. An Artefact. O’Keefe thought that this could not be real! There must be something messing with his recordings of the brain’s electrical signals. Maybe the power outlets in the walls or something. But he checked everything, found that if he put the same rat in the same box the next day, the same set of neurons in the hippocampus would become excited in that same place. This would happen the next day and the next day and in different labs. O’Keefe concluded that these must be real. Since these neurons fire in certain places, he decided to call them “place cells”. The place where they fire is called a “place field”.
Place cells are great. As I walk around my room, I have a set of place cells firing when I am exactly in the middle of my room, and a set of place cells firing here when I am a step left of the room’s center, a set of place cells firing in the north corner of the room, and at every place. And since these sets of place cells are kind of different from each other, it allows my brain to make a map and to know where I am in relation to my room!
Furthermore, place cells function in darkness. Blind people have place cells.
What allows place cells and place fields to happen in the brain?
The Discovery of Grid Cells by May-Britt and Edvard Moser
Decades after the discovery of place cells, the Mosers had a will and a way through their lab in Norway.
They had rats doing the same chocolate foraging task around an arena. The Mosers recorded electrical activity from a brain region known as the medial entorhinal cortex because it seems to send its signals to the hippocampus. Could medial entorhinal cortex signals be involved in space circuits of the brain?
Through these experiments, the Mosers found something! There were cells in the medial entorhinal cortex that seemed to be everywhere in their firing, not firing in particular places like place cells.
What a pain. An artefact. Surely, something in the brain could not be this regular, repeating pattern! But like O’Keefe, they repeated the experiment, did a lot of checking and trying this out on different days. They had the same results. Since the pattern seemed to be some sort of triangle grid, they decided to call these cells “grid cells”.
Moser and Moser moseyed on over to present this finding at a conference. One of the scientists there looked at this and said he thought there might be hexagon-shaped symmetry. He advised the group to have these rats search for chocolate in a larger arena to see what pattern was really there.
The Mosers tried having their rats forage in a larger space and found that indeed, there seemed to be a repeating pattern of hexagons. The hexagon patterns are known as “grid fields.” The brain’s ability to makes grid fields allows it to make place fields.
For the discovery of place cells and grid cells, O’Keefe and the Mosers won the Nobel prize in 2014. Place cells and grid cells have been found not only in rats, but in mice, bats, monkeys, humans, and more!
Some other cells involved in spatial navigation
Place cells and grid cells let us know where we are. In navigation systems, it helps to know where you are heading, otherwise we may find ourselves going in the opposite direction! The brain also has a sort of compass, thanks to cells known as head direction cells.
The head direction cells are not quite like a literal compass that will always tell you what north, south, east, and west are. But the head direction cells will let you know where your head direction is in relation to your surroundings. It doesn’t matter whether your eyes are looking up or down or left or right. It doesn’t matter if your body is positioned in one way or another. As long as you are facing the same direction, the same ensemble of head direction cells will fire, which allows you to know which direction you are facing.
If everything about the room you are in was shifted ninety degrees clockwise, your head direction cell activity would adjust to this by shifting according to landmarks in the room.
We also keep track of our speed as we go through our space because we have speed cells! It is quite amazing that whether you are walking or running through the same route, your brain will know where you are, even if your running is much faster than your walking. Yes, our brains have a speedometer.
When you successfully find your way from one place to another, remember what got you there. More than a car, a bus, or your feet, but also your brain, which contains neurons to help you to interpret space. Speed. Direction. Position. And where you are in relation to your world.
Wherever you are and wherever you have been, may you be well in all the places you’ll go.
References and further reading:
https://www.nobelprize.org/prizes/medicine/2014/press-release/
http://www.scholarpedia.org/article/Head_direction_cells
http://www.scholarpedia.org/article/Grid_cells
https://www.sciencedirect.com/science/article/pii/S0960982212012079
https://www.nature.com/articles/nature14622
https://www.sciencedirect.com/science/article/abs/pii/0014488676900558
https://www.sciencemag.org/news/2006/06/ants-stilts
The author has illustrated all of the images in this article. This article has been adapted from the author’s talk presented at Nerd Nite Ann Arbor, February 2019. When NEURO+SCIENCE was an active Medium publication, this story was curated there. The views expressed in this article are solely those of the author and do not necessarily reflect those of Nerd Nite Ann Arbor, OmarLab, the University of Michigan, Intvo, Valence Vibrations, or SquadNest.
