We approached this question by reconsidering the past 25 years of work in the electrophysiology of human memory. We categorized studies by whether they employed invasive or non-invasive methods, and whether they used a memory success contrast or a specific measure of associative memory. We discovered that findings of theta power decreases were mostly isolated to intracranial studies analyzing memory success. Otherwise, theta power increases were found in studies of scalp EEG, MEG, and intracranial EEG that utilized associational contrasts.
