As we move around, we have a sense of where we are and we are able to plan where we need to go. The brain provides us with this sense thanks to a map of the local space. This map was discovered in the 1970s here at UCL by John O’Keefe, who received a Nobel Prize for it last year. The brain keeps this map in a region called the Hippocampus. The map is made of neurons, each of which fire when navigation traverses a certain location in space. The brain maintains and updates this map using multiple cues. One of these cues is by counting steps from a known location. Another cue is given by the landmarks that our eyes see. But how does the brain go from images of landmarks on the eyes to a sense of location in the world?
In the Carandini and Saleem laboratories, we investigate this question with the help of mice who navigate virtual reality worlds while we record the activity of neurons in their brain, from visual regions to the Hippocampus. The advantages of virtual reality are not only practical (it allows us to study the brain while the head is not moving) but also fundamental. Indeed, in virtual reality, we control precisely what the eyes see at any given moment, and we can create places that are different in space but appear exactly identical from a visual standpoint, and thus appear different only to parts of the brain that go beyond pure vision to aid navigation. Moreover, in virtual reality we can break the rules that apply in the real world. For instance, we can dissociate the walking speed from the speed of motion in the virtual world. This dissociation helps us understand how neurons in various parts of the brain respond to the visual motion experienced by the eye and to the movement created by the body while navigating.
Through these investigations we hope to understand a fundamental operation performed by our brains on a regular basis: using our eyes to locate ourselves in the environment and making appropriate decisions to navigate to this or that place. It is a challenge at the forefront of contemporary neuroscience, as it involves understanding how a myriad neurons in multiple parts of the brain work together to achieve a natural behavior.