The oscillatory correlates of human memory have been intensively studied for over 25 years using both non-invasive (scalp electroencephalography, EEG and magnetoencephalography, MEG) and invasive (intracranial EEG, iEEG or electrocorticography, ECoG) recording techniques (see Box 3 for a discussion on the origin of theta effects observed with both kinds of methods). These studies have shown variable evidence for theta oscillations during human episodic memory; some studies report memory-related theta increases while others report decreases. In many cases memory-related theta increases and decreases were found in the same study, depending on when and where in the brain oscillatory power was examined.
