HIPPOCAMPAL THETA-GAMMA PHASE-AMPLITUDE COUPLING CODES FOR THE DISTANCE TO HIDDEN GOAL LOCATIONS IN HUMAN INTRACRANIAL EEG

Successful navigation often relies on planning and executing sequences of movements through known locations to reach a hidden goal. However, the neural mechanisms that support the dynamic construction and maintenance of these sequential action plans are not yet clear. Using an abstract navigation task and non-invasive MEG recordings, we have previously shown that model-based planning of this kind might be mediated by hippocampal theta-gamma phase-amplitude coupling (PAC). Here, we replicate those findings using a more ethological navigation task and intracranial EEG recordings from the hippocampus in pre-surgical epilepsy patients. Specifically, we asked patients to encode and retrieve the location of several distinct objects in a desktop virtual reality environment. We find that theta-gamma PAC on hippocampal electrode contacts increases as participants navigate towards remembered goal locations during retrieval, but not as visible goal locations are approached during encoding. Importantly, this relationship is only present during accurate navigation and not observed on adjacent electrode contacts in the amygdala or lateral temporal lobe. In addition, we find that gamma power decreases and shows evidence of theta phase precession in the posterior hippocampus during the same period. Each of these results is consistent with the planned sequence of upcoming locations being encoded within gamma bursts at consecutive phases of the hippocampal theta rhythm during memory-guided navigation. As such, these findings suggest that hippocampal theta-gamma PAC may support sequential planning during goal-directed behaviour, paralleling related findings of goal-directed “theta-sweeps” in rodents.