Phase-coupling of theta-gamma EEG rhythms during short-term memory processing.

Full Abstract

Because of the importance of oscillations as a general phenomenon of neuronal activity the use of EEG spectral analysis is among the most important approaches for studying human information processing. Usually, oscillations at different frequencies occur simultaneously during information processing. Thus, the question for synchronisation of different frequencies by phase coupling and its possible functional significance is of primary importance. An answer may be given by bispectral analysis. Estimation of the (cross-) bispectrum allows to identify synchronised frequencies and possibly, the existence of non-linear phase coupling of different oscillators. Previous studies have demonstrated the simultaneous occurrence of slow (4-7 Hz) and fast (20-30 Hz) oscillations at frontal and prefrontal electrode positions during memory processing. However, interrelations between these rhythms have not been investigated up to now. In order to test short-term memory, the Sternberg task with random figures and number words was carried out on 10 female subjects. During the task EEG was recorded. Power and bispectral analyses from frontal, prefrontal and frontopolar regions were performed off-line. Increased power was found in both the theta and the gamma bands. Strong phase-coupling between theta at Fz and gamma at F3 and at Fp1, respectively, was shown for memorising number words by means of cross-bicoherence. A possible reason for this is an amplitude modulation of gamma frequencies by slow oscillations. The correspondent coherence analysis between the envelope of gamma frequencies at Fp1 and the raw EEG at Fz supports this presumption. This finding is interpreted as an EEG aspect of the functional linking between the prefrontal areas and the G.cinguli (as part of the limbic system), which are both extremely important for memory functions.

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Author information

Author/s: Schack, B (B); Vath, N (N); Petsche, H (H); Geissler, H-G (HG); Möller, E (E);

Affiliation: Institute of Medical Statistics, Computer Science and Documentation, University of Jena, Jahnstr. 3, D-07740, Jena, Germany. schack(-atsign-)imsid.uni-jena.de

Journal and publication information

Publication Type: Comparative Study; Journal Article; Research Support, Non-U.S. Gov't

Journal: International journal of psychophysiology : official journal of the International Organization of Psychophysiology (Int J Psychophysiol), published in Netherlands. (Language: eng)

Reference: 2002-May; vol 44 (issue 2) : pp 143-63

Dates: Created 2002/03/22; Completed 2003/03/24; Revised 2006/11/15;

PMID: 11909647, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adult
Analysis of Variance
Cortical Synchronization
Electroencephalography - classification
Evoked Potentials - physiology
Female
Frontal Lobe - physiology
Humans

Humans
Memory, Short-Term - physiology
Oscillometry
Reaction Time - physiology
Signal Processing, Computer-Assisted
Stochastic Processes
Theta Rhythm
Verbal Learning

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