Richards, J.E. (2002). Cortical source analysis of ERP of individual participants in psychophysiological experiments. Society for Psychophysiological Research, Washington, D.C.
The identification of cortical sources of event-related potentials (ERP) can be used to study psychologically-related brain activity with non-intrusive measures in traditional psychophysiological tasks. These analyses usually are done on measures averaged over a group of many participants. This presentation will show some of the techniques necessary for analyzing this in individual participants. Its use will be illustrated in a study of antisaccade-related presaccadic-ERP in children and adults, and identification of cortical sources in infant participants. There are four steps necessary for analyzing cortical sources for individual participants. First, knowledge of individual's head structure is necessary to correlate scalp-recorded ERP with brain structure. This may be accomplished via structural MRIs of individuals, or by "warping" external head measurements on individuals to representative brain topographies (representative or "average" MRI, stereotaxic atlas). Second, numerical techniques quantify the ERP for the individual. This may be participant-based grand averages. The methods include spatial component analysis (independent component analysis, principal component analysis), which can result in measures of component activation for a single participant or single trials. Third, a variety of source techniques exist that may be used to locate the cortical source of the scalp-recorded ERP. These include numerical methods and commercial computer packages. Finally, the locations found in the source analysis must be related to the cortical structures for that individual.