Electroencephalographic patterns of equine sleep: comparative description and neurophysiological implications of recumbent and standing sleep

The present study aimed to describe and compare the electroencephalographic patterns of sleep in horses during recumbent and standing positions, identifying the cortical dynamics and spectral characteristics associated with each stage. Eight clinically healthy adult horses were monitored through polysomnographic EEG recordings, using a double-banana montage with subcutaneous needle electrodes. Sleep stages were classified according to spectral and morphological criteria analogous to human scoring standards, with one sleep cycle analyzed per horse.

REM sleep was posture-dependent, with complete paradoxical patterns observed only in recumbent horses. In standing animals, a REM-like state was identified, marked by rapid eye movements but cortical hypoactivation and absence of muscle atonia. Quantitative analysis revealed that N1 and N2 accounted for approximately 90% of total sleep duration, while N3 and REM represented smaller fractions.

Standing horses exhibited longer light sleep stages and a smaller proportion of N3 sleep. These findings demonstrate that equine sleep architecture is highly posture-dependent, and behavioral postures such as sternal or lateral recumbency cannot be reliably used as proxies for specific EEG sleep stages. The study provides a methodological framework to support future investigations and facilitate comparisons of equine sleep physiology across studies and species.

This study was financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Finance Code 001 and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) - Process 2021/11323–1. Department of Internal Medicine, School of Veterinary Medicine and Animal Science, University of São Paulo – FMVZ/USP, São Paulo, Brazil Tiago Marcelo Oliveira, Roberta Carvalho Basile, Beatriz Constante Souza, Yuri Ferreira Vicentini, Angela Perrone Barbosa & Raquel Yvonne Arantes Baccarin Correspondence to Tiago Marcelo Oliveira. The authors declare no competing interests.

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If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Oliveira, T.M., Basile, R.C., Souza, B.C. et al.