Discriminant analysis and equivalent source localization of the EEG related to cognitive functions

Discriminant analysis and EEG source localization methods were employed to compare groups of normal subjects during different cognitive conditions usi ng 43-channel EEG recordings in the alpha (8-13 Hz) frequency band. Recordi ngs were obtained from 69 dextral females during 2 passive conditions, Eyes -Open and Eyes-Closed, and 2 active conditions, Word-Finding and Dot-Locali zation. The cross-spectral matrix between all of the electrode sites was us ed to characterize the EEGs obtained during each condition. The subjects we re partitioned into training and test sets and quadratic discriminant funct ions were constructed from the training sets to classify the EEGs. The disc riminant functions successfully classified both the training and test sets at rates approaching 80%. The classification was repeated using only the di agonal (power spectral) elements of the cross-spectral matrices in the disc riminant functions and this approach was successful in discriminating betwe en the EEGs from the passive cognitive conditions but failed to discriminat e between the EEGs from the active conditions. Source localization using a modified MUSIC algorithm indicated that the centers of brain electrical act ivity that distinguished the Eyes-Closed condition from the Eyes-Open condi tion were located in the medial occipital and right frontal regions. Center s of electrical activity that distinguished the Word-Finding condition from the Dot-Localization condition were located in the right medial posterior and left temporal regions. Validation of the locations of the centers of ac tivity was accomplished by repeating the classification procedures using th e spatial patterns generated on the scalp by dipole current sour ces placed at these locations.