Theta Oscillations in Human Memory

• Published in: Trends in cognitive sciences Vol. 24; no. 3; pp. 208 - 227
• Main Authors: Herweg, Nora A., Solomon, Ethan A., Kahana, Michael J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.03.2020
• Subjects: associative memory; Electroencephalography; Humans; intracranial EEG; Memory, Episodic; Mental Recall; SME; spectral tilt; theta; Theta Rhythm; SME; associative memory; theta; spectral tilt; intracranial EEG
• ISSN: 1364-6613; 1879-307X
• DOI: 10.1016/j.tics.2019.12.006

Theta frequency (4–8 Hz) fluctuations of the local field potential have long been implicated in learning and memory. Human studies of episodic memory, however, have provided mixed evidence for theta’s role in successful learning and remembering. Re-evaluating these conflicting findings leads us to conclude that: (i) successful memory is associated both with increased narrow-band theta oscillations and a broad-band tilt of the power spectrum; (ii) theta oscillations specifically support associative memory, whereas the spectral tilt reflects a general index of activation; and (iii) different cognitive contrasts (generalized versus specific to memory), recording techniques (invasive versus noninvasive), and referencing schemes (local versus global) alter the balance between the two phenomena to make one or the other more easily detectable. Influential theories state that human declarative memory relies on the same neural machinery as spatial navigation and specifically implicate the theta rhythm in memory formation for associations between sequentially visited places and experiences events.Electrophysiological studies in humans, however, paint a complicated picture of theta’s role in episodic memory.Whereas some studies observe increases in theta power associated with successful memory, other studies observe a spectral tilt of the power spectrum with increased high frequency and decreased low-frequency power during successful memory formation or retrieval.Here, we reconcile these findings by considering the distinction between narrow-band theta oscillations and co-occurring broad-band effects. We show how recording methods as well as analytical choices may alter the balance between the two phenomena.