Cognitive Neuroscience Society
New York City, NY
April 4-7, 2003
Julie Onton and Scott Makeig ,
Swartz Center for Computational Neuroscience
Institute for Neural Computation
University of California San Diego
La Jolla CA 92093-0961
{julie,scott}@sccn.ucsd.edu
Distributed EEG Dynamics of Short-Term Memory
In this study, we investigated EEG dynamics occurring during a variation of the Sternberg task. Each trial consisted of a sequence of 8 letters (SOA 1400 ms), 3-7 of which were to be memorized. The remainder of the letters were a different color, indicating they should be ignored. Following presentation of the eighth letter, subjects viewed a fixation point for 2-4 s, then responded to a presented probe letter by pressing either of two response buttons to indicate whether or not the probe letter had been memorized. Applied to the 71-channel EEG data, Independent Component Analysis (ICA) extracted 15-25 components whose spatial projections strongly resembled projections of single equivalent dipoles. In some components with occipital and parietal projections, power at alpha and beta frequencies increased during presentations of 'ignore' letters, while decreasing after 'memorize' letters. Several patterns of event-related phase coherence between independent components were found following all event types (e.g. memorize, ignore, or probe letters). Some component pairs showed stronger cross-coherences in the theta range (4-8 Hz) following 'memorize' letters than 'ignore' letters. Cross-coherence after presentation of the probe letter was significantly stronger than after a 'memorize' letter. This was most striking between occipital and parietal components in the theta frequency range. Cross-coherence at higher frequencies (25-35 Hz) between certain components was exclusive to pre- and post-probe periods. These results confirm that distributed patterns of EEG dynamics contribute to retention and retrieval of memorized letters.