Interhemispheric theta coherence in the hippocampus for successful object-location memory in human intracranial encephalography.

Our knowledge concerning visual-spatial memory related phase synchronization within the ipsilateral hippocampus or between contralateral hippocampi during memory encoding in humans is currently limited. The present study examines the relationship between phase synchronization within the hippocampus and memory performance during virtual navigation in an object-location memory navigation task using intracranial depth electrodes in human subjects. Specifically, we focus on the phase synchronization ratio between periods when the target object was in and out of visual focus. Our findings indicate that there is a significant relationship between this phase synchronization ratio and object-location memory performance in the theta band (p = 0.015, R = -0.71), but not in the delta or alpha bands. Importantly, this theta coherence has a significant linear relationship with memory performance between contralateral hippocampus electrode pairs (p = 0.006, R = -0.77), but not ipsilateral electrode pairs (p = 0.79, R = -0.09). In addition, this theta coherence has a significant linear relationship with memory performance during stationary periods (p = 0.002, R = -0.82), but not movement periods (p = 0.10, R = -0.51). These findings suggest that, during navigation, interhemispheric hippocampal theta coherence when stationary and focusing on the target object may be a critical determinant of successful object-location memory.