Dissociation between phase-locked and nonphase-locked alpha oscillations in a working memory task
Article first published online: 21 APR 2009
Copyright © 2009 Wiley-Liss, Inc.
Human Brain Mapping
Volume 30, Issue 10, pages 3417–3425, October 2009
How to Cite
Freunberger, R., Fellinger, R., Sauseng, P., Gruber, W. and Klimesch, W. (2009), Dissociation between phase-locked and nonphase-locked alpha oscillations in a working memory task. Hum. Brain Mapp., 30: 3417–3425. doi: 10.1002/hbm.20766
- Issue published online: 11 SEP 2009
- Article first published online: 21 APR 2009
- Manuscript Accepted: 30 JAN 2009
- Manuscript Revised: 17 DEC 2008
- Manuscript Received: 3 SEP 2008
- Deutsche Forschungsgemeinschaft (DFG). Grant Number: DFG-KL1856/1-1
The functions of human alpha oscillations (∼10 Hz) were related to cognitive processes such as memory and top-down control. Recent models suggest that alpha phase serves as a mechanism especially relevant for the timing of neural activity, whereas alpha amplitude is important for the inhibition of task-irrelevant brain areas. This study investigates directly the influence of top-down modulation on phase-locked and nonphase-locked alpha rhythms. We conducted an EEG experiment where subjects performed a working memory task. In the encoding phase of the task subjects had to learn presented pictures of nonliving objects that could later be asked to be retrieved. We varied the top-down modulation by including cues indicating either to remember or to forget (not to remember) the next following item. Spectral analyses showed that nonremember cues elicited pronounced alpha amplitude increase compared to remember cues. Furthermore, phase-locking in low frequencies, especially in the alpha range (7–12 Hz), was stronger for remember as opposed to not-to-remember items. In conclusion, we propose that alpha amplitude reflects top-down modulated inhibition and that alpha phase is important for the exact timing of neural activity and can be related to binding processes. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc.