Scalp electrical recording during paralysis: quantitative evidence that EEG frequencies above 20 Hz are contaminated by EMG.
OBJECTIVE
To identify the possible contribution of electromyogram (EMG) to scalp electroencephalogram (EEG) rhythms at rest and induced or evoked by cognitive tasks.


METHODS
Scalp EEG recordings were made on two subjects in presence and absence of complete neuromuscular blockade, sparing the dominant arm. The subjects undertook cognitive tasks in both states to allow direct comparison of electrical recordings.


RESULTS
EEG rhythms in the paralysed state differed significantly compared with the unparalysed state, with 10- to 200-fold differences in the power of frequencies above 20 Hz during paralysis.


CONCLUSIONS
Most of the scalp EEG recording above 20 Hz is of EMG origin. Previous studies measuring gamma EEG need to be re-evaluated.


CONCLUSIONS
This has a significant impact on measurements of gamma rhythms from the scalp EEG in unparalysed humans. It is to be hoped that signal separation methods will be able to rectify this situation.
Whitham
Emma M
EM
Department of Neurology, Flinders University and Medical Centre, GPO Box 2100, Adelaide, SA 5042, Australia.
Pope
Kenneth J
KJ
Fitzgibbon
Sean P
SP
Lewis
Trent
T
Clark
C Richard
CR
Loveless
Stephen
S
Broberg
Marita
M
Wallace
Angus
A
DeLosAngeles
Dylan
D
Lillie
Peter
P
Hardy
Andrew
A
Fronsko
Rik
R
Pulbrook
Alyson
A
Willoughby
John O
JO
D000161:Acoustic Stimulation / Q000379:methods; D016477:Artifacts; D004569:Electroencephalography; D004576:Electromyography; D006801:Humans; D008297:Male; D008606:Mental Processes; D009466:Neuromuscular Blocking Agents; D010243:Paralysis / Q000175:diagnosis / Q000503:physiopathology* / Q000523:psychology; D010775:Photic Stimulation; D012535:Scalp / Q000503:physiopathology*
D009466:Neuromuscular Blocking Agents