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World Congress of
Psychophysiology
Montreal, CA
July
29 – Aug. 3, 2002
Scott Makeig, Institute for Neural Computation, University of California San Diego, La Jolla CA
Symposium on EEG
Coherence
Brainstorms:
Independent EEG processes transiently synchronize in response to cognitive
challenges
Noninvasively recorded high-density EEG signals contain a
wealth of information about cortical synchronization in multiple frequency
bands and cortical domains. However, the goal of event-related coherence methods
for modeling functional macroscopic brain dynamics is compromised by the
use of scalp EEG signals that each sum activities occurring in multiple EEG
domains. The approach I present here uses independent component analysis to
separate the activity of different domains of cortical synchrony and to remove
non-neural artifacts, followed by wavelet-based time/frequency analysis and
single-trial based visualization methods to detect brain dynamic events
occurring in response to cognitive challenges. An
important class of such events are coherent theta band phenomena
that briefly organize synchronous brain activity within
otherwise-independent cortical domains in response to cognitive challenges.
I give examples from EEG responses to task-relevant stimuli in stimulus
detection, memory encoding and Erickson flanker tasks. I show, in
particular, that theta dynamic events underlie the error-related negativity
(ERN) following errors committed in forced choice responses under time
pressure. Source location estimates of the EEG domains linked by these dynamic
events suggest they form transient fronto-parietal
networks that may serve to regulate top-down attentional
re-tuning of motor and perceptual brain areas in light of the perceived
consequences of previous attentional orientation.
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