Cognitive neuroscientists have long grappled with a fundamental question: Does human declarative memory rely on the same neural machinery as spatial navigation? If so, does the theta oscillation observed in the hippocampus and in connected cortical brain regions during navigation also emerge during memory encoding and retrieval? Evidence from scalp EEG and MEG has generally suggested “yes”; theta oscillations support episodic memory. But many intracranial EEG studies suggest “no”; theta power actually decreases during successful memory encoding and retrieval. At stake is our understanding of a core brain structure -- does the MTL have a domain-general function that uses the same neural elements to process associations between arbitrary inputs, or is it functionally segmented to process spatial navigation in one way, and memory in an entirely different way?
