Qualitative and quantitative characteristics of the electroencephalogram in normal horses during spontaneous drowsiness and sleep.
Authors: Williams D C, Aleman M, Holliday T A, Fletcher D J, Tharp B, Kass P H, Steffey E P, LeCouteur R A
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: EEG characterisation during equine sleep and drowsiness Understanding the electroencephalographic (EEG) signatures of different sleep states in horses has remained poorly characterised despite their clinical relevance, prompting Williams and colleagues to establish normative EEG parameters across vigilance states using non-invasive electrode placement in five neurologically normal horses monitored overnight with concurrent video recording. The researchers identified distinct quantitative differences between slow wave sleep (SWS) and both drowsiness and rapid eye movement (REM) sleep, with SWS demonstrating significantly different frequency and power characteristics (P < 0.05); notably, SWS was accompanied by second-degree heart block and transient events analogous to those recognised in human EEGs, whilst drowsiness and REM sleep exhibited similar low-amplitude beta activity with prominent approximately 4 Hz background activity. One horse demonstrated multiple partial collapses during standing REM sleep, highlighting the postural challenges of paradoxical sleep in this species. Beyond providing essential control data for future sedative and anaesthetic investigations, these normative parameters offer clinicians a practical foundation for interpreting equine EEGs in hospital settings, recognising that the sleep patterns documented—being from horses in unfamiliar environments—may reasonably reflect behaviours encountered in clinical practice. Farriers, veterinarians, and equine rehabilitation professionals should recognise that apparent neurological irregularities during rest, particularly heart conduction changes during deep sleep, may represent normal physiological variants rather than pathology.
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Practical Takeaways
- •Normative EEG data established for horses can serve as baseline for interpreting EEGs in clinical and research settings
- •Cardiac arrhythmias (second-degree heart block) may be normal variants during deep sleep in horses and should not necessarily trigger concern
- •Sleep behavior in unfamiliar environments (like clinical settings) may differ from home environment; consider this when interpreting clinical findings
Key Findings
- •Slow wave sleep (SWS) was significantly different in frequency and power from drowsiness and REM sleep (P < 0.05)
- •Second-degree heart block was associated with SWS and transient EEG events commonly recognized in humans
- •Drowsiness and REM sleep showed similar EEG patterns with low-amplitude beta activity and prominent ~4 Hz activity
- •Standing REM sleep in one horse was associated with numerous partial collapses