Qualitative and quantitative characteristics of the electroencephalogram in normal horses during spontaneous drowsiness and sleep.
BACKGROUND
The influence of sleep on the equine electroencephalogram (EEG) has not been well documented.


OBJECTIVE
The objectives were to develop a noninvasive method of electrode placement for recording the EEG in horses and to establish normal EEG parameters for the various states of vigilance. Findings are compared with previously published reports on equine sleep based on electrocorticography (ECoG).


METHODS
Five neurologically normal horses.


METHODS
Overnight EEGs were recorded digitally in association with simultaneous videotaping of the horses' behavior. Data were analyzed by visual inspection, states of vigilance were identified, and representative segments were quantitatively processed. Transient EEG events were examined.


RESULTS
Slow wave sleep (SWS) was significantly different (P < .05) in frequency and power from drowsiness and rapid eye movement (REM) sleep. Second-degree heart block was associated with SWS as were transient events commonly recognized in EEGs of humans. Drowsiness and REM sleep were similar. In both, background activity was low-amplitude beta activity admixed with prominent activity of approximately 4 Hz. Standing REM sleep was associated with numerous partial collapses in 1 horse.


CONCLUSIONS
Normative data for several states were described and probable benign variants identified. This information will serve as control data for sedative and anesthetic studies in this species. The sleep patterns observed during this study are those of horses removed from their usual surroundings, and thus may represent those encountered in a clinical environment.
Williams
D C
DC
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. dcwilliams@ucdavis.edu
Aleman
M
M
Holliday
T A
TA
Fletcher
D J
DJ
Tharp
B
B
Kass
P H
PH
Steffey
E P
EP
LeCouteur
R A
RA
D000818:Animals; D004569:Electroencephalography / Q000662:veterinary*; D005260:Female; D006736:Horses / Q000502:physiology*; D008297:Male; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology; D014851:Wakefulness / Q000502:physiology