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Theta wave

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An EEG theta wave

Theta waves generate the theta rhythm, a neural oscillation in the brain that underlies various aspects of cognition and behavior, including learning, memory, and spatial navigation in many animals.[1][2] It can be recorded using various electrophysiological methods, such as electroencephalogram (EEG), recorded either from inside the brain or from electrodes attached to the scalp.

At least two types of theta rhythm have been described. The hippocampal theta rhythm is a strong oscillation that can be observed in the hippocampus and other brain structures in numerous species of mammals including rodents, rabbits, dogs, cats, and marsupials. "Cortical theta rhythms" are low-frequency components of scalp EEG, usually recorded from humans. Theta rhythms can be quantified using quantitative electroencephalography (qEEG) using freely available toolboxes, such as, EEGLAB or the Neurophysiological Biomarker Toolbox (NBT).

In rats, theta wave rhythmicity is easily observed in the hippocampus, but can also be detected in numerous other cortical and subcortical brain structures. Hippocampal theta waves, with a frequency range of 6–10 Hz, appear when a rat is engaged in active motor behavior such as walking or exploratory sniffing, and also during REM sleep.[3] Theta waves with a lower frequency range, usually around 6–7 Hz, are sometimes observed when a rat is motionless but alert. When a rat is eating, grooming, or sleeping, the hippocampal EEG usually shows a non-rhythmic pattern known as large irregular activity or LIA. The hippocampal theta rhythm depends critically on projections from the medial septal area, which in turn receives input from the hypothalamus and several brainstem areas. Hippocampal theta rhythms in other species differ in some respects from those in rats. In cats and rabbits, the frequency range is lower (around 4–6 Hz), and theta is less strongly associated with movement than in rats. In bats, theta appears in short bursts associated with echolocation.

In humans, hippocampal theta rhythm has been observed and linked to memory formation[4][5] and navigation.[6] As with rats, humans exhibit hippocampal theta wave activity during REM sleep.[7] Humans also exhibit predominantly cortical theta wave activity during REM sleep.[8] Increased sleepiness is associated with decreased alpha wave power and increased theta wave power.[8] Meditation has been shown to increase theta power.[9]

The function of the hippocampal theta rhythm is not clearly understood. Green and Arduini, in the first major study of this phenomenon, noted that hippocampal theta usually occurs together with desynchronized EEG in the neocortex, and proposed that it is related to arousal. Vanderwolf and his colleagues, noting the strong relationship between theta and motor behavior, have argued that it is related to sensorimotor processing. Another school, led by John O'Keefe, have suggested that theta is part of the mechanism animals use to keep track of their location within the environment. Another theory links the theta rhythm to mechanisms of learning and memory (Hasselmo, 2005). This theory states that theta waves may act as a switch between encoding and recall mechanisms, and experimental data on rodents [10] and humans [11] support this idea. Another study on humans has showed that theta oscillations determine memory function (encoding or recall) when interacting with high frequency gamma activity in the hippocampus.[12] These findings support the idea that theta oscillations support memory formation and retrieval in interaction with other oscillatory rhythms. These different theories have since been combined, as it has been shown that the firing patterns can support both navigation and memory.[13]

In human EEG studies, the term theta refers to frequency components in the 4–7 Hz range, regardless of their source. Cortical theta is observed frequently in young children.[14] In older children and adults, it tends to appear during meditative, drowsy, hypnotic or sleeping states, but not during the deepest stages of sleep. Theta from the midfrontal cortex is specifically related to cognitive control and alterations in these theta signals are found in multiple psychiatric and neurodevelopmental disorders.[15]

  1. ^ Seager, Matthew A.; Johnson, Lynn D.; Chabot, Elizabeth S.; Asaka, Yukiko; Berry, Stephen D. (2002-02-05). "Oscillatory brain states and learning: Impact of hippocampal theta-contingent training". Proceedings of the National Academy of Sciences of the United States of America. 99 (3): 1616–20. Bibcode:2002PNAS...99.1616S. doi:10.1073/pnas.032662099. PMC 122239. PMID 11818559.
  2. ^ Winson, J. (1978-07-14). "Loss of hippocampal theta rhythm results in spatial memory deficit in the rat". Science. 201 (4351): 160–3. Bibcode:1978Sci...201..160W. doi:10.1126/science.663646. PMID 663646.
  3. ^ Squire, Larry R. (17 December 2012). Fundamental neuroscience (4th ed.). Amsterdam: Elsevier/Academic Press. p. 1038. ISBN 978-0-12-385871-9. OCLC 830351091.
  4. ^ Lega, Bradley C. (2011). "Human hippocampal theta oscillations and the formation of episodic memories". Hippocampus. 22 (4): 748–761. doi:10.1002/hipo.20937. PMID 21538660. S2CID 13316799.
  5. ^ Tesche, C. D.; Karhu, J. (2000-01-18). "Theta oscillations index human hippocampal activation during a working memory task". Proceedings of the National Academy of Sciences. 97 (2): 919–924. Bibcode:2000PNAS...97..919T. doi:10.1073/pnas.97.2.919. PMC 15431. PMID 10639180.
  6. ^ Ekstrom, Arne D. (2005). "Human hippocampal theta activity during virtual navigation". Hippocampus. 15 (7): 881–889. CiteSeerX 10.1.1.535.1693. doi:10.1002/hipo.20109. PMID 16114040. S2CID 2402960.
  7. ^ Lomas T, Ivtzan I, Fu CH (2015). "A systematic review of the neurophysiology of mindfulness on EEG oscillations" (PDF). Neuroscience & Biobehavioral Reviews. 57: 401–410. doi:10.1016/j.neubiorev.2015.09.018. PMID 26441373. S2CID 7276590.
  8. ^ a b Hinterberger T, Schmidt S, Kamei T, Walach H (2014). "Decreased electrophysiological activity represents the conscious state of emptiness in meditation". Frontiers in Psychology. 5: 99. doi:10.3389/fpsyg.2014.00099. PMC 3925830. PMID 24596562.
  9. ^ Lee DJ, Kulubya E, Goldin P, Goodarzi A, Girgis F (2018). "Review of the Neural Oscillations Underlying Meditation". Frontiers in Neuroscience. 12: 178. doi:10.3389/fnins.2018.00178. PMC 5890111. PMID 29662434.
  10. ^ Manns JR, Howard MW, Eichenbaum H (November 2007). "Gradual changes in hippocampal activity support remembering the order of events". Neuron. 56 (3): 530–40. doi:10.1016/j.neuron.2007.08.017. PMC 2104541. PMID 17988635.
  11. ^ Kerrén C, van Bree S, Griffiths BJ, Wimber M (November 2022). "Phase separation of competing memories along the human hippocampal theta rhythm". eLife. 11. doi:10.7554/eLife.80633. PMC 9671495. PMID 36394367.
  12. ^ Saint Amour di Chanaz L, Pérez-Bellido A, Wu X, Lozano-Soldevilla D, Pacheco-Estefan D, Lehongre K, Conde-Blanco E, Roldan P, Adam C, Lambrecq V, Frazzini V, Donaire A, Carreño M, Navarro V, Valero-Cabré A, Fuentemilla L (May 2023). "Gamma amplitude is coupled to opposed hippocampal theta-phase states during the encoding and retrieval of episodic memories in humans". Curr Biol. 33 (9): 1836–43.e6. doi:10.1016/j.cub.2023.03.073. PMID 37060906.
  13. ^ Buzsáki, György; Moser, Edvard I. (2013). "Memory, navigation and theta rhythm in the hippocampal-entorhinal system". Nature Neuroscience. 16 (2): 130–8. doi:10.1038/nn.3304. PMC 4079500. PMID 23354386.
  14. ^ OREKHOVA, E; STROGANOVA, T; POSIKERA, I; ELAM, M (May 2006). "EEG theta rhythm in infants and preschool children". Clinical Neurophysiology. 117 (5): 1047–62. doi:10.1016/j.clinph.2005.12.027. PMID 16515883. S2CID 19204190.
  15. ^ McLoughlin, Gráinne; Gyurkovics, Máté; Palmer, Jason; Makeig, Scott (2021). "Midfrontal Theta Activity in Psychiatric Illness: An Index of Cognitive Vulnerabilities Across Disorders". Biological Psychiatry. 91 (2): 173–182. doi:10.1016/j.biopsych.2021.08.020. PMID 34756560.

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