Dr Francesco Gobbo and Rufus Mitchell-Heggs, working in Prof Richard Morris’s group and in collaboration with Prof Simon Schultz at Imperial College London, have recently had a paper published in the Proceedings of the National Academy of Science which offers a novel solution to one of the grand challenges in research on spatial navigation is encoded in the brain. The solution involves recording from large numbers of brain cells in a region of the brain called the hippocampus. It has long been known that single neurons in the hippocampus respond to the individual’s location in space. These – called place-cells – appear to provide information about where a person or animal is located. Other cells in adjacent brain regions appear to code for the metric of space such as speed, other properties of the environment such as obstacles, or the heading direction of the navigator. However, knowing where you are and what direction you are moving through an environment is not the same as deciding where to go. Schematic of the miniscope technology In an experiment using a technique called calcium-imaging, which enables the activity of very large numbers of brain cells to be monitored simultaneously and across days, rats were trained to approach one of three different goals on separate days. The correct position changed on a daily basis and in a random manner. The animals were then tasked with discovering which was the correct position that day. As expected, over the route to the rewarded location Place cells were observed as being active – encoding the animal’s instantaneous location. The new finding was that in a brief decision-making window, before the animal embarked on its journey, the activity of a separate population of neurons could collectively be used to predict the rewarded location that the animal was going, specifically on occasions when the animal chose correctly. Using a machine learning technique called neural manifold learning they found that the neural population activity at the decision-making time and the rewarded location were remarkably similar. Incorrect choices were not predicted suggesting that, when they occurred, mistakes were random. In particular, the team found that the active neurons mapped out the journey of the correct future path rather than the memory of a previous path. Their results imply that this activity is not simply anticipatory or a recall of immediate past, but rather represent a “mental scenario” of possible choices. The “thought out” paths replayed by the hippocampus during decision making. These findings indicate that neurons in the hippocampus are not just involved in representing the space that the animal is in, but also involved in deciding where they go.Article link: https://www.pnas.org/doi/10.1073/pnas.2212152119 Publication date 11 Nov, 2022
