A recent study published in the journal Nature Neuroscience provides insight into how the brain handles bodily navigation and corrects errors by making adjustments that allow it to locate its starting point. The study was conducted by psychology professor Jeffrey Taube and his former postdoctoral assistant Stephane Valerio.
In the experiment, Taube's team trained rats to perform a food-foraging task in which they left a home base to find a pellet and returned with it to the starting location. The team then tracked the activity of 27 of the rats' brains' head-directional cells, which are located in several parts of the brain and act as the brain's compass. Using microelectrodes, they monitored both when the rats returned safely to the home base and when they miscalculated direction.
"We are interested in how the brain knows your spatial orientation in the environment how you know where you are, what direction you're facing and things like that," Taube, whose research spanned four years, said. "You need to know your orientation as the first step in being able to navigate from one place to another. If you're in A before you go to B, you have to ask yourself, Where is A, what direction am I facing at A and what sort of trajectory path takes me to B?'"
Taube's research led to two significant findings. The experiment showed that the head-directional cells can help predict if an animal will take the correct route back to its home base, he said. As soon as the rat took its first step, they could tell based on the firing of those cells if it would make an error and by how much. These cells differ from location cells, which Taube and Valerio did not utilize in their experiment.
The study's second major finding was that when the rats made small errors in their trajectories, the rats' cells corrected themselves when the rats returned to their refuge, according to Taube. He said that when a larger error was made, however, the cells remapped, keeping the error in the cells' orientations.
"It's sort of like if you get lost out in the world and then you find your way back to your tent," he said. "If you made a small error, then probably your system remaps to the setting of the environment where your tent is. But let's say you made a large error and you come back to where your campsite is with a large error, then your system won't reset."
The study has identified the two spatial orientation processes that go on in the brain, which future researchers interested in understanding how the brain represents space will be able to examine, according to Taube. The findings could also lead to more knowledge about certain human conditions, such as Alzheimer's disease, strokes and other diseases that affect navigational abilities.
"Not that this will help them immediately, but in terms of trying to understand what processes these people might go through or try when they get lost and they try to reorient, it helps us understand a little bit of what they might be going through," he said.
While to some, it may be initially unclear how research on rats translates to human spatial navigation, there is a clear link that has drawn many top neuroscientists use rats in their studies, according to psychology professor Patrick Cavanagh.
"Research on navigation in rats is one of the hottest areas in neuroscience," Cavanagh said.
Other researchers may begin to use the distinction between "resetting" and "remapping" when moving forward in their work on the subject, according to Taube.
Michael Shinder, currently a postdoctoral research assistant in Taube's lab, said that the study of the brain's handling of navigation has seen many recent discoveries over the past 10 years.
"The idea is that you have a representation of space, but to build that you need to understand your orientation where you are and that's led to a resurgent interest," he said.
Taube and Valerio's paper is particularly important because it is one of the first studies to clearly link head-direction cells and behavioral orientation, according to Shinder.
"You have your orientation, but no one had connected that to navigation in general," he said. "To the largest extent possible, this paper does make the connection. It's a real necessary piece."
