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Spatio-temporal correlations in human gamma band electrocorticograms
V Menon1, W J Freeman, B A Cutillo
1EEG Systems Laboratory, San Francisco, CA 94105, USA.
Electroencephalography and Clinical Neurophysiology
|February 1, 1996
Summary
Researchers found no global gamma band patterns for perceptual categorization in human ECoG. Instead, they observed intermittent, localized synchronization between electrodes, suggesting current technology may not detect these subtle brain signals.
Area of Science:
- Neuroscience
- Electrophysiology
- Cognitive Science
Background:
- Animal electrocorticogram (ECoG) studies link spatial gamma band patterns (>20 Hz) to perceptual categorization.
- Similar phenomena in human ECoG remain largely uncharacterized, particularly regarding spatio-temporal correlations.
Purpose of the Study:
- To investigate spatio-temporal correlations in the 20-50 Hz gamma band of human ECoG for perceptual categorization.
- To determine if globally correlated activity underlies behavior in human ECoG.
Main Methods:
- ECoGs recorded from 64-electrode subdural grids (1 cm spacing) in 2 epilepsy patients during a somatosensory discrimination task.
- Bootstrap techniques employed to analyze spatial and temporal correlation characteristics.
- Principal Component Analysis (PCA) used to extract spatial patterns.
Main Results:
- No evidence of globally correlated gamma band activity (20-50 Hz) linked to behavior was found.
- Spatial patterns extracted via PCA were not classifiable by stimulus type.
- Spatially and temporally intermittent synchronization observed between electrodes within 1 cm regions, with significant correlations at 1 cm and 1.4 cm distances, but not ≥2 cm.
Conclusions:
- Spatially correlated activity domains for perceptual categorization in human gamma band ECoG appear limited to <2 cm surface diameters.
- Intermittent synchronization suggests activity is not solely due to volume conduction.
- Current scalp-based technologies are insufficient; subdural arrays with <5 mm spacing are needed to measure potential gamma band spatial patterns.