Far-field electrophysiology reflects top-down control

For forty years, much human electrophysiologic thinking has been based on the concept that EEG data recorded from the scalp following sensory stimulation are dominated by successive far-field correlates of bottom-up brain sensory processing, as represented in evoked potential (EP) averages. I will present evidence for an alternate view that human EEG data are dominated by oscillatory processes relating to time-varying, top-down control of cortical dynamics and attention. This view suggests a reorientation of scientific and engineering focus towards modeling brain dynamics of humans as active operators rather than as passive perceivers and programmed responders. Such research presents new engineering challenges. There is a need, first, to understand and model the process of partial phase resetting of ongoing and intermittent nonlinear oscillatory processes, and more generally, of inter-process synchronization. Methods we have developed or integrated for EEG research, including independent component analysis (ICA) and time/frequency analysis, now allow detection and modeling of such brain dynamic events from high-dimensional electrical data collected noninvasively from the human scalp. It is probable that real time signal processing capable of separating EEG processes from non-brain signals and of monitoring brain synchronization events may allow high-level cognitive monitoring that could be used in man-machine interfaces and for neuropsychological training.