Matteo Carandini, PhD
Professor
Department of Neuroscience
University College London
(January 30, 2018)
From Vision to Navigation: A Journey in the Cerebral Cortex
It happens to all of us at some point. If, while out walking or driving, we come to a supposedly familiar place from a different direction than usual, it can take a few minutes to reorient. This is accomplished with sight – our visual system helps us to make sense of our environment. Doctor Carandini investigates how visual signals are transformed into estimates of position. He has found that neurons in the mouse visual cortex show preference for certain spatial positions. This work highlights that more of the brain may be involved in navigation than previously expected.
The visual system and the navigational system are two of the most studied pathways in neuroscience. A key region of the visual system is the primary visual cortex, where myriad neurons deconstruct images into fragments and respond according to the fragment that falls in their receptive field. The navigational system, in turn, centers on a region of the hippocampus, where neurons exhibit place fields, i.e. are selective for the position that an animal occupies in the world. These notions are well understood, and their discoveries awarded with Nobel Prizes in 1981 and 2014.
These two systems, however, must talk to one another: a major role of vision is to guide navigation, and navigation is strongly driven by vision. How are visual signals transformed into estimates of position? To study this transformation, Doctor Carandini’s lab recorded from large populations of neurons in the cortex of mice that navigated environments in virtual reality. To their surprise, they found that neurons as early as in primary visual cortex exhibit preferences for spatial position. These preferences strengthen as signals proceed towards parietal cortex, where responses become entirely related to navigation, coding for combinations of the animal’s position and heading direction.
Navigation signals in visual cortex correlate strongly with signals in the hippocampus, where cells have those well-known preferences for spatial position, and are closely related to the animal’s subjective estimate of location. Signals related to navigation, therefore, appear much earlier than expected in the visual system, and are intimately related to the animal’s own estimate of position in the world. The presence of such navigational signals as early as in a primary sensory area suggests that these signals permeate sensory processing in the cortex. The brain, or at least the brain of a mouse, may be devoted to navigation to a much larger extent than anticipated.