Gamma rhythms are not integral to EEG spindle phenomena.
OBJECTIVE
Gamma rhythms (30-100 Hz) have been shown to be associated with spindling activity induced by picrotoxin. To determine if gamma power is unique to picrotoxin spindles or is an integral part of physiological and pathological spindling activity we analysed and compared the strength and brain distribution of gamma EEG power during 4 spindling activities in the rat.


METHODS
The electroencephalogram (EEG) was recorded from rats with chronically implanted electrodes during natural sleep, barbiturate anaesthesia, during naturally occurring absence epilepsy spike and wave discharges and following the systemic application of picrotoxin. Spectral analysis was applied off-line to compare the strength and brain distribution of gamma EEG power during the 4 spindling activities.


RESULTS
Each spindle type contained significantly different levels of gamma power. Gamma power was significantly increased over background levels during picrotoxin spindles, slightly increased during absence spindles, slightly decreased during sleep spindles and significantly suppressed during barbiturate spindles


CONCLUSIONS
Changes in the power of gamma frequencies during spindle types suggest that gamma frequencies are neither the cause of nor an integral part of a spindle. They appear to be correlated with levels of consciousness and may contribute to the process of epileptogenesis.


CONCLUSIONS
The findings are consistent with high frequency EEG activity being related to seizure-tendency.
Mackenzie
L
L
Department of Medicine and Centre for Neuroscience, Flinders University, P.O. Box 2100, Adelaide SA 5001, Australia.
Pope
K J
KJ
Willoughby
J O
JO
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D004569:Electroencephalography / Q000187:drug effects / Q000379:methods*; D008297:Male; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D010852:Picrotoxin