Living in Flatland
Our brains are terrible at understanding height, a new study reveals – and the research also explains the evolutionary trade-offs related to our flattened sense of orientation.
By studying two types of brain cells that fire as we move from place to place, the researchers found that our intuitive sense of relative location hardly changes as we move vertically – and our intuitive sense of distance doesn’t seem to change at all:
It looks like the brain’s knowledge of height in space is not as detailed as its information about horizontal distance, which is very specific. It’s perhaps akin to knowing that you are “very high” versus “a little bit high” rather than knowing exact height.
And the higher we get, the harder it is to get a clear sense of just how high we are. (I’m gonna let that statement speak for itself.)
As reported in the journal Nature Neuroscience, a team led by Kathryn Jeffery at University College London studied the firing patterns of two types of neurons in the hippocampus as mice explored two kinds of environments: a climbing wall and a helix (as I’ve mentioned before, some types of mouse brain activity are very reliable at predicting how human brains behave).
This particular study focused on grid cells, which help brains get a sense of relative distance, and place cells, which fire when the animal arrives at a specific (you guessed it) place. The researchers found that place cells didn’t fire much as the mice moved vertically – and that grid cells fired exclusively in response to horizontal movement:
It seems that grid cell odometry (and by implication path integration) is impaired or absent in the vertical domain, at least when the rat itself remains horizontal. These findings suggest that the mammalian encoding of three-dimensional space is anisotropic.
In other words, mice (and probably humans) measure distance mainly on a plane that’s roughly level with their eyes. Like a broken odometer, our place and grid cells simply don’t “clock” vertical movement. As far as those cells are concerned, we might as well be living in Flatland.
The upside of this is that when it comes to horizontal movement – such as navigating a maze – mice and men can keep a detailed memory for specific spots, and orient themselves very precisely relative to other locations. Unless you’re like me, that is, and need GPS to find your way from the front door to the driveway.
Anyway, what does all this lack of height-sensing mean for those with vertigo – or just your basic acrophobia? Well, as Jeffery points out, we clearly do have some instinctive sense of “very high” as opposed to “a little high” – but exactly how our brains encode that difference isn’t quite as well understood.
It’s likely that our sense of height has more to do with depth perception, and with an instinctive fear of visible drop-offs, than with any sense of personal distance or location – in other words, we aren’t able to use our bodies to sense how much higher we’re climbing, but we can look down/out and see that the ground ahead is farther away than we’d like it to be. Thus, one way to calm vertigo is simply to close your eyes.
Without that visual feedback, you’ll be back to Flatland in no time.