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Cerebral Cortex Advance Access originally published online on December 3, 2007
Cerebral Cortex 2008 18(8):1843-1855; doi:10.1093/cercor/bhm213
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© 2007 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Effects of Working Memory Load on Oscillatory Power in Human Intracranial EEG

Jed A. Meltzer1, Hitten P. Zaveri2, Irina I. Goncharova2, Marcello M. Distasio3, Xenophon Papademetris4,3, Susan S. Spencer2, Dennis D. Spencer5 and R. Todd Constable1,3,4,5

1 Interdepartmental Neuroscience Program, 2 Departments of Neurology, 3 Biomedical Engineering, 4 Diagnostic Radiology, 5 Neurosurgery, Yale University, New Haven, CT 06510, USA

Address correspondence to Jed A. Meltzer, PhD, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Building 10, room 5C410, 10 Center Drive, Bethesda, MD 20852, USA. Email: jed.meltzer{at}aya.yale.edu.

Studies of working memory load effects on human EEG power have indicated divergent effects in different frequency bands. Although gamma power typically increases with load, the load dependency of the lower frequency theta and alpha bands is uncertain. We obtained intracranial electroencephalography measurements from 1453 electrode sites in 14 epilepsy patients performing a Sternberg task, in order to characterize the anatomical distribution of load-related changes across the frequency spectrum. Gamma power increases occurred throughout the brain, but were most common in the occipital lobe. In the theta and alpha bands, both increases and decreases were observed, but with different anatomical distributions. Increases in theta and alpha power were most prevalent in frontal midline cortex. Decreases were most commonly observed in occipital cortex, colocalized with increases in the gamma range, but were also detected in lateral frontal and parietal regions. Spatial overlap with group functional magnetic resonance imaging results was minimal except in the precentral gyrus. These findings suggest that power in any given frequency band is not a unitary phenomenon; rather, reactivity in the same frequency band varies in different brain regions, and may relate to the engagement or inhibition of a given area in a cognitive task.

Key Words: alpha • BOLD • ECoG • fMRI • gamma • Sternberg • theta


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