Figure 1. Hippocampal and orbitofrontal cognitive mapping.

a | In spatial tasks, many hippocampal neurons exhibit spatially specific firing. The firing fields (place fields, represented in the image by coloured ellipsoids) of these ‘place cells’ tile the environment. At an ensemble level, the firing of place cells encodes the animal’s position in the environment. b | In a reinforcement-learning framework, the ensemble firing of spatially tuned place cells could be thought of as encoding an environmental state space: that is, it would represent both individual states (the circumscribed portions of the environment within which each individual place cell is most active) and how they connect to one another. States in this example environmental state space are coloured to correspond to the place fields shown in part a. c | As animals traverse the environment, the activity of hippocampel neurons could be thought of as representing trajectories through the environmental state space. The figure shows raster plots that illustrate the firing of seven individual hippocampal cells representing two different state space trajectories (coloured to match parts a. and b.). The trajectories overlap as the animal travels along the central arm of a T-maze but diverge for left and right turns. Different sets of place cells represent positions to the left and right of the choice point. In a similar manner, the activity of non-spatially tuned hippocampal neurons could represent position in a more abstract, non-spatial state space. d | Similarly, as animals are engaged in decision- making tasks, orbitofrontal cortex (OFC) neurons that are active during the performance of actions or other task events (such as the presentation of cues and outcomes) could encode the current task state. e In contrast to the example state space shown in part b, which was defined entirely by position in the environment, the state space for an operant decision- making task might be structured around important task events, include ing actions (such as making an initial nose poke in an odour sample port). cues (such as the presentation of an odour) and outcomes (such as the delivery of a liquid reward). In these examples, the states represented might be the ‘odour-sampling state’ or the ‘reward-delivery state’. f | Because different OFC neurons are activated by specific actions and events (for example, they fire in response to particular odour cues rather than to general odour presentation), the trajectories through state space encoded by OFC ensembles vary depending on the animal’s actions (in this case, a left or right response) and on the information received from the environment.