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The Journal of Neuroscience, July 30, 2008, 28(31):7781-7787; doi:10.1523/JNEUROSCI.1631-08.2008

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Behavioral/Systems/Cognitive
Asymmetric Amplitude Modulations of Brain Oscillations Generate Slow Evoked Responses

Ali Mazaheri and Ole Jensen

F. C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, NL-6500 HB Nijmegen, The Netherlands

Correspondence should be addressed to Ole Jensen, F.C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands. Email: ole.jensen{at}fcdonders.ru.nl

Electrophysiological data measured by electroencephalography and magnetoencephalography (MEG) are widely used to investigate human brain activity in various cognitive tasks. This is typically done by characterizing event-related potentials/fields or modulations of oscillatory activity (e.g., event-related synchronization) in response to cognitively relevant stimuli. Here, we provide a link between the two phenomena. An essential component of our theory is that peaks and troughs of oscillatory activity fluctuate asymmetrically; e.g., peaks are more strongly modulated than troughs in response to stimuli. As a consequence, oscillatory brain activity will not "average out" when multiple trials are averaged. Using MEG, we demonstrate that such asymmetric amplitude fluctuations of the oscillatory alpha rhythm explain the generation of slow event-related fields. Furthermore, we provide a physiological explanation for the observed asymmetric amplitude fluctuations. In particular, slow event-related components are modulated by a wide range of cognitive tasks. Hence, our findings provide new insight into the physiological basis of cognitive modulation in event-related brain activity.

Key words: electroencephalography; EEG; magnetoencephalography; MEG; event-related potential; ERP; event-related field; ERF; alpha; beta; synchronization

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Received April 15, 2008; revised May 24, 2008; accepted June 17, 2008.

Correspondence should be addressed to Ole Jensen, F.C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands. Email: ole.jensen{at}fcdonders.ru.nl

Related articles in J. Neurosci.:

Amplitude Asymmetry: A Direct Link between Ongoing Oscillatory Activity and Event-Related Potentials?

Iris Grothe and Michael Plöchl
J. Neurosci. 2008 28: 13025-13027. [Full Text]  

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