When we drive somewhere new, we navigate by referring to a two-dimensional map that accounts for distances only on a horizontal plane. According to research published online in August in Nature Neuroscience, the mammalian brain seems to do the same, collapsing the world into a flat plane even as the animal skitters up trees and slips deep into burrows.

“Our subjective sense that our map is three-dimensional is illusory,” says Kathryn Jeffery, a behavioral neuroscientist at University College London who led the research. Jeffery studies a collection of neurons in and around the rat hippo­campus that build an internal representation of space. As the animal travels, these neurons, called grid cells and place cells, respond uniquely to distance, turning on and off in a way that measures how far the animal has moved in a particular direction.

Past research has focused on how these cartographic cells encode two-dimensional space. Jeffery and her col­leagues decided to look at how they respond to changes in altitude. To do this, they enticed rats to climb up a spiral staircase while the scientists collected electrical recordings from single cells. The firing pattern encoded very little in­formation about height.

The finding adds evidence for the hypothesis that the brain keeps track of our location on a flat plane, which is defined by the way the body is oriented. If a squirrel, say, is running along the ground, then scampers straight up a tree, its internal two-dimensional map simply shifts from the horizontal plane to the vertical. Astronauts are some of the few humans to de­scribe this experience: when they move in space to “stand” on a ceiling, they report a moment of disorientation before their mental map flips so they feel right side up again.

Researchers do not know yet whether other areas of the brain encode altitude or whether mammals simply do not need that information to survive. “Maybe an animal has a mosaic of maps, each fragment of which is flat but which can be oriented in the way that’s appropriate,” Jeffery speculates. Or maybe in our head, the world is simply flat.

7 Comments

1. 1. jtdwyer 08:38 AM 1/29/12

   This brief news article's explanation is hardly convincing: standing on one's head in space requires an entirely inverted topographical mapping of their spatial environment, whether it's encode in two or three dimensions.
   
   I suggest that the researchers include marine mammals and bats in their study - I strongly suspect that a two dimensional topographical encoding of their environment would do them little good.
   
   Generalizing their study's conclusions about rat brains to apply to all mammals indicates more to me about the structure of 'behavioral neuroscientists' brains than the brains all humans. I've seen examples of this kind of analysis before...

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2. 2. billsmith in reply to jtdwyer 04:01 PM 1/29/12

   
   @jtdwyer
   
   If you will read the journal article's summary (or even its title), you will see that they did /not/ say that all mammal brains have a completely 2D representation of the world. What the paper ("Anisotropic encoding of three-dimensional space by place cells and grid cells") did say was that a particular area of the brain does not necessarily use a mapping that devotes equal processing power to all dimensions. Rather, the representation in this area of the brain is anisotropic (directionally dependent).
   
   Because all mammals have very similar basic brain structures (even though the proportions can be quite different), it's not a stretch to suppose that humans also have grid cells and place cells that represent space in a directionally-dependent way. This part, though, is for future studies. (Only a limited number of these studies have been done on the representation of space in the human brain because one first has to find patients who need electrodes in their brains for medical reasons.)
   
   As you suggest, rats may have spatial memory more centered on whisker touch, humans on sight, and bats and dolphins on echolocation. This does not necessarily speak to the type of mental map(s) involved. Hunting bats, for instance, seem to filter out side clutter and speed differences to percieve signals from a tightly-focused, forward-facing, 1D beam. However, it's also quite likely that these different mammals' representations, whatever they might be, are also not isotropic.
   
   "Anisotropic encoding of three-dimensional space by place cells and grid cells"
   http://www.nature.com/neuro/journal/v14/n9/full/nn.2892.html
   
   "Cellular networks underlying human spatial navigation"
   http://www.nature.com/nature/journal/v425/n6954/full/nature01964.html
   
   "Evidence for grid cells in a human memory network"
   http://www.nature.com/nature/journal/v463/n7281/full/nature08704.html
   

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3. 3. shibindinesh 10:25 PM 1/29/12

   Thanks to billsmith for the links to the papers. But i was wondering why Scientific American has published this story in Jan 2012 when the original paper to the topic was published long back in August 2011.

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4. 4. glundby 02:30 PM 1/31/12

   I have observed my dogs as they return to home, a flat at 9th floor, the door to the right. The dog runs ahead up the stairs to first floor and stops at the door to the right. When I walk on up, it runs ahead and stops at the door to the right. This is repeated for each floor all the way to the flat. This might not be a scientific observation, but I bet that dogs evolution have not wasted brain cells on 3D mappings. (Luckily the lift sometimes did not work, giving me the opportunity to make this observations.)

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5. 5. jtdwyer in reply to billsmith 07:09 PM 2/8/12

   Yes, thanks for the links to $96 worth of Nature Neuroscience and Nature articles, but I can neither afford to purchase them nor subscribe to those journals. I am also not a university student or an employee of any corporation who can freely access group subscriptions. I am also unable to frequent public libraries that might offer journal access. I'm merely a retired SA subscriber.
   
   My comments were addressed directly to this SA article summarizing those articles (I presume, since they were not referenced).
   
   This article does quote Kathryn Jeffery, a behavioral neuroscientist at University College London who led the research:
   “Our subjective sense that our map is three-dimensional is illusory...”
   
   I do not think that conclusions based on studies of rat brains (or any other single subject species) can be generalized to apply to human beings or other species.

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6. 6. rwstutler 10:31 PM 2/9/12

   JT's perverse skepticism, ignorance, and protests of poverty asside, it makes perfect evolutionary sense for brains to use the simplest solution and to use it recursively for modeling in 3D, rather than to evolve more complex mechanisms.

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7. 7. jtdwyer 08:54 AM 2/10/12

   On the other hand, 2D spatial mapping might be a distinct disadvantage for tree dwelling primates, even if they are only ignorant monkeys.

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