a b s t r a c tHuman hippocampal theta oscillations play a key role in accurate spatial coding. Associative encoding involves similar hippocampal networks but, paradoxically, is also characterized by theta power decreases. Here, we inves tigated how theta activity relates to associative encoding of place contexts resulting in accurate navigation. Using MEG, we found that slow theta (2 5 Hz) power negatively correlated with subsequent spatial accuracy for vir tual contextual locations in posterior hippocampus and other cortical structures involved in spatial cognition. A rare opportunity to simultaneously record MEG and intracranial EEG in an epilepsy patient provided crucial in sights: during power decreases, slow theta in right anterior hippocampus and left inferior frontal gyrus phase led the left temporal cortex and predicted spatial accuracy. Our findings indicate that decreased slow theta activ ity reflects local and long range neural mechanisms that encode accurate spatial contexts, and strengthens the view that local suppression of low frequency activity is essential for more efficient processing of detailed information.

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