Does the brain maintain a separate goal map for future destinations in addition to maps of current position and direction?

Why would the brain need a separate goal map?

Knowing where you are is not the same as knowing where you are going. The hippocampus provides a detailed map of the current position and nearby trajectories, but its role in specifying the destination has been questioned [1]. A separate goal map allows the brain to maintain a precise estimate of a target location that may be far away and beyond the range of the senses, which is essential for accurate navigation [1].

This division of labor is supported by the discovery of neurons in the rat orbitofrontal cortex that encode the subsequent goal destination throughout navigation [1]. These goal representations emerge before navigation begins and are maintained by destination-specific neural ensemble dynamics; briefly disrupting them at the start of a journey causes navigational errors [1]. This suggests that the orbitofrontal cortex is part of an internal goal map that works alongside the hippocampal position map [1].

How does the goal map work during navigation?

The goal map is not a passive store of a location; it actively guides behavior. In rats, orbitofrontal goal representations persist even when the animal makes a mistake, predicting the incorrect destination at the beginning of an error trial [1]. This indicates that the goal map can drive navigation toward a chosen target, whether correct or not, and that it operates independently of immediate sensory input [1].

Other brain regions contribute to goal-directed navigation in different ways. In mice, the posterior parietal cortex contains activity patterns that relate to intended trajectories, separate from actual physical movements [3]. When a brain-machine interface was used to switch control of navigation to parietal cortex activity, mice could immediately navigate toward goals without learning, and decoded trajectories decoupled from their physical movements [3]. This suggests that parietal cortex activity can represent a planned path to a goal, distinct from the current position and direction [3].

How do goal maps differ from position maps?

The hippocampus is traditionally viewed as the brain's map of current position, but recent work shows it can also carry signals related to future locations. In mice using a brain-machine interface to navigate directly from hippocampal activity, place codes rapidly reconfigured to form new representations that discarded locomotion-related signals [4]. This suggests that hippocampal codes are not fixed to current movement but can be activated internally to predict future locations [4].

However, the goal map appears to be at least partly separate from the hippocampal position map. In rats, orbitofrontal goal representations are distinct from hippocampal place codes and are maintained by their own neural dynamics [1]. Furthermore, the hippocampus itself may process goal-related value information in a region-specific manner: inactivating the intermediate hippocampus impairs value-dependent navigation toward a high-value goal more severely than inactivating the dorsal hippocampus [2]. This indicates that the hippocampus contributes to goal-directed behavior, but the precise goal location may be represented elsewhere, such as in the orbitofrontal cortex [1].

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