Honeycomb maze reveals role of hippocampus in navigation decisions: Neuroscientists unearth how hippocampal place cells support flexible navigation in rats

Researchers at the Sainsbury Wellcome Centre at University College London have discovered that the hippocampus creates a vector-based representation to support animals to make optimal navigation decisions.

Published today in Nature, the researchers report results which go a long way to solving the problem of how hippocampal place cells contribute to flexible navigation. They report that during navigation to a goal, place cells represent information about the direction and distance to the goal in addition to their well-established representation of the animal’s current location. They uncovered this goal-directed information using the honeycomb maze, a behavioural apparatus, which breaks up navigation to a goal into a succession of binary choices.

The maze consists of 61 individually raisable platforms. While on each individual platform, the rat is given the choice of two adjacent platforms to move towards the goal and, to be successful, should choose the one closest to the goal direction. The animal continues through these iterative choices until the goal is reached. The task thus allows systematic analysis of the navigational decisions an animal makes on its progress to the goal. At each choice point, the place cells report direction and distance to the goal as well as the animal’s current location.

“The honeycomb maze is very different to other behavioural tasks in neuroscience as we can use it to present animals with a series of choices of platforms to navigate towards a goal. This allows us to look at iterative decision-making during navigation,” said Dr Jake Ormond, Senior Research Fellow in the O’Keefe lab and first author on the paper.

While rats were taking part in the honeycomb maze task, Dr Ormond and Professor John O’Keefe recorded from place cells, a class of neurons first discovered by Professor O’Keefe that collectively form an internal representation of space. These recordings allowed them to look at how spatial representation relates to spatial action in place cell activity.

The activity of a subgroup of individual place cells creates a vector field oriented to unmarked locations called convergence sinks (ConSinks) dotted around the maze and surrounding space but concentrated near the goal. At the place cell population level, the overall vector field points to the goal location from every point on the maze providing a signal that the animal can follow to get to the goal.

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