“It’s a really welcome addition to the growing field of rodent virtual reality.” So says Northwestern University neurobiologist Daniel Dombeck in commenting on a new study, published yesterday by Science, that compares what goes on in rats’ brains when they navigate digitally created spaces with what goes on in their noggins when they navigate the real world. Rats, like humans, have place cells, which are neurons that fire reliably at particular locations and, it’s believed, play a key role in the brain’s creation of cognitive maps. The study reveals that place cells are considerably less active in virtual reality (VR) than in the real world (RW):
When Mayank Mehta, a neurophysicist at the University of California (UC), Los Angeles, compared the activity of place cells in rats running along a real, linear track with place cell activity in the rats running in virtual reality, he saw some surprising differences. In the real world, about 45% of the rats’ place cells fired at some point along the track. In virtual reality, only 22% did. “Half of the neurons just shut up,” he says.
Individual place cells also behaved radically differently in VR than they do in RW:
On a real track, [a particular place cell] would fire when [the rat] had taken two steps away from the start [of the track], and then again when the animal reached the same spot on its return trip. But in virtual reality, something odd happened. Rather than firing a second time when the rat reached the same place on its return trip, [the cell] fired when the rat was two steps away from the opposite end of the track … That’s like the same place cell in your brain firing when you’ve taken two steps away from your door and then when you’ve taken two steps away from your car. Instead of encoding a position in absolute space, the place cell seems to be keeping track of the rat’s relative distance along the (virtual) track. [Mehta] says, “This never happens in the real world.”
Mehta thinks that the difference may stem from the lack of “proximal cues” — environmental smells, sounds, and textures that provide clues to location — in the digital world:
And considering that when those cues disappear, the rat’s cognitive map appears to change from one based on absolute space to one based on relative distance, proximal cues might be the key component to how those mental maps work in the real world.
Rats’ sensory perception of the world differs from that of people — rats don’t see very well, for instance — and that (among other things) makes it hard to know whether human brains react to VR and RW in the same way. But the study at least hints at the richness of our perception of the world — a richness that is very much embodied in our physical being even though it may be hidden from our conscious mind. To me, this raises an important but rarely heard question about so-called augmented reality (AR), particularly the use of computers to add an extra layer of visual information to our conscious perception of the world: Is augmented reality also diminished reality? In other words, by adding input to one (conscious) layer of perception, do you end up degrading other (conscious and/or unconscious) layers of perception?
Is RW + AR > RW or is RW + AR < RW?
And does it matter?
Photo by UCLA Neurology.