The neural machinery responsible for the formation of associations between high-dimensional representations resides primarily in the medial temporal lobe (MTL), containing the hippocampus, entorhinal, perirhinal, and parahippocampal cortices. Communication and processing within these regions, and between these regions and neocortical association areas, has been linked to episodic memory [1] (see Glossary) and spatial navigation [2,3] -- both processes that involve associations either between the sensory and cognitive components that comprise an event memory, or between the features that mark specific locations in space. And potentially key to these functions is a physiological signature called the theta rhythm -- a 4–8 Hz oscillation in the local field potential (LFP) that was first characterized in rodents in the 1930s (see Box 1).
