Across-trial averaging of event-related EEG responses and beyond

Magn Reson Imaging. 2008 Sep;26(7):1041-54. doi: 10.1016/j.mri.2008.01.011. Epub 2008 May 13.


Internally and externally triggered sensory, motor and cognitive events elicit a number of transient changes in the ongoing electroencephalogram (EEG): event-related brain potentials (ERPs), event-related synchronization and desynchronization (ERS/ERD), and event-related phase resetting (ERPR). To increase the signal-to-noise ratio of event-related brain responses, most studies rely on across-trial averaging in the time domain, a procedure that is, however, blind to a significant fraction of the elicited cortical activity. Here, we outline the key concepts underlying the limitations of time-domain averaging and consider three alternative methodological approaches that have received increasing interest: time-frequency decomposition of the EEG (using the continuous wavelet transform), blind source separation of the EEG (using Independent Component Analysis) and the analysis of event-related brain responses at the level of single trials. In addition, we provide practical guidelines on the implementation of these methods and on the interpretation of the results they produce.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Cortical Synchronization*
  • Electroencephalography*
  • Evoked Potentials / physiology*
  • Humans
  • Signal Processing, Computer-Assisted*