Execution of new trajectories toward a stable goal without a functional hippocampus

The hippocampus is a critical component of a mammalian spatial navigation system, with the firing sequences of hippocampal place cells during sleep or immobility constituting a “replay” of an animal's past trajectories. A novel spatial navigation task recently revealed that such “replay” sequences of place fields can also prospectively map onto imminent new paths to a goal that occupies a stable location during each session. It was hypothesized that such “prospective replay” sequences may play a causal role in goal‐directed navigation. In the present study, we query this putative causal role in finding only minimal effects of muscimol‐induced inactivation of the dorsal and intermediate hippocampus on the same spatial navigation task. The concentration of muscimol used demonstrably inhibited hippocampal cell firing in vivo and caused a severe deficit in a hippocampal‐dependent “episodic‐like” spatial memory task in a watermaze. These findings call into question whether “prospective replay” of an imminent and direct path is actually necessary for its execution in certain navigational tasks.