Decomposition and evaluation of activity in multiple event-related trials

It is generally accepted that evoked and induced activations represent different aspects of cerebral functions during an Event Related Potentials (ERP) experiment. Independent Component Analysis (ICA) has been successfully applied to event related electroencephalography (EEG) to decompose it into a sum of spatially fixed and temporally independent components that can be attributed to underlying cortical activity. A major problem in the application of ICA is the stability of estimated independent components. In this paper we exploited the split-half approach to assess component stability. We used different measures quantifying both phase and energy aspects of the ERP, in order to distinguish evoked from induced oscillations. We applied these measures to the stable independent components derived from a dataset of progressive Mild Cognitive Impairment (PMCI) and elderly controls. We found reduced energy in the induced theta activity in PMCI subjects, in accordance with previous studies. In addition, PMCI subjects presented lower phase-locking values and diminished late alpha band energy in contrast to controls.