title: EEG coherency II: experimental comparisons of multiple measures.
abstract: OBJECTIVE
  A concentric spheres model was used in an earlier paper to estimate the effects of volume conduction, reference electrode and spatial filtering on different EEG coherence measures. EEG data are used here to verify theoretical predictions.
  
  
  METHODS
  Three EEG data sets were: (1) 64 channel, recorded during 7 alternating periods of resting and mental calculation. (2) 128 channel, for comparison of eyes open versus eyes closed coherence. (3) 128 channel, recorded during deep sleep (stages 3 and 4) and REM.
  
  
  RESULTS
  The directions of large scale (lobeal) coherency changes between brain states are relatively independent of coherence measure. However, coherence between specific electrode pairs is sensitive to method and frequency. Average reference and digitally linked mastoids provide reasonable semi-quantitative estimates of large-scale neocortical source coherence. Close bipolar, Laplacian, and dura image methods remove most reference electrode and volume conduction distortion, but may underestimate coherence by spatial filtering.
  
  
  CONCLUSIONS
  Each EEG coherence method has its own potential sources of error and provides coherence estimates for different neural population sizes located in different locations. Thus, studies of coherence and brain state should include several different kinds of estimates to take full advantage of information in recorded signals.
authors.affiliation: Department of Biomedical Engineering, Tulane University, New Orleans, LA, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Nunez
authors.forename: R B
authors.initials: RB
authors.lastname: Silberstein
authors.forename: Z
authors.initials: Z
authors.lastname: Shi
authors.forename: M R
authors.initials: MR
authors.lastname: Carpenter
authors.forename: R
authors.initials: R
authors.lastname: Srinivasan
authors.forename: D M
authors.initials: DM
authors.lastname: Tucker
authors.forename: S M
authors.initials: SM
authors.lastname: Doran
authors.forename: P J
authors.initials: PJ
authors.lastname: Cadusch
authors.forename: R S
authors.initials: RS
authors.lastname: Wijesinghe
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D002648:Child; D004569:Electroencephalography; D006801:Humans; D012890:Sleep / Q000502:physiology