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Automated detection of sleep states from olfactory brain waves

An algorithm based on olfactory bulb brain activity can distinguish awake, REM, and non-REM sleep states in mice

PLOS

Scientists have developed a completely automated technique for real-time detection of sleep/wake states in freely moving mice. Conducted by Karim Benchenane, Sophie Bagur and colleagues at the National Centre for Scientific Research in Paris, the study, publishing on November 8 in the open-access journal, PLOS Biology, describes how local brain activity in the olfactory bulb is enough to accurately classify mouse vigilance states into wake, REM sleep, and non-REM sleep. The olfactory bulb is a brain structure that transmits information related to the sense of smell to the rest of the brain, and in mice projects forward from under the cerebral cortex, towards the nasal cavity.

Understanding the transition between wake and sleep is important for medical and clinical applications ranging from surgical anesthesia to sleep disorders such as insomnia. Although much has been learned from mouse models, tracking sleep/wake states in rodents and the transitions between the two is currently labor-intensive and suffers from variability both between scoring methods and between individual scorers. Using real-time local field potential recordings from the mouse olfactory bulb, the new method relies entirely on brain activity and a preset algorithm, thus making it more efficient, more objective and more reliable than current methods.

After discovering that changes in gamma waves from the olfactory bulb are a reliable marker for sleep/wake states, the team developed an automated sleep-scoring algorithm that performed better than standard classification methods. Unlike standard methods that rely on recordings of muscle activity, the new method did not misclassify rodent "freezing" behavior as sleep. They also found that while brain activity from the hippocampus was the best signal for distinguishing REM and non-REM sleep, beta waves from the olfactory bulb could do the job almost as well, meaning that the automated system only requires one implanted wire per mouse.

Once the system was established, the scientists were able to use it for several applications, including detecting the depth of anesthesia and characterizing the differences between wake-sleep and sleep-wake transitions. The automated real-time classification system thus has the potential to have wide-ranging applications in sleep research.

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In your coverage please use this URL to provide access to the freely available article in PLOS Biology: http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2005458

Citation: Bagur S, Lacroix MM, de Lavilléon G, Lefort JM, Geoffroy H, Benchenane K (2018) Harnessing olfactory bulb oscillations to perform fully brain-based sleep-scoring and real-time monitoring of anaesthesia depth. PLoS Biol 16(11): e2005458. https://doi.org/10.1371/journal.pbio.2005458

Funding: Ecole Normale Superieure (grant number). for SB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Ministère de l'Enseignement Supérieur et de la Recherche Scientifique (grant number). for GL and MML. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Agence Nationale de la Recherche (grant number ANR-12-BSV4-0013-02 [AstroSleep], ANR-16-CE37-0001 [Cocode], ANR-10-LABX-54 MEMO LIFE, and ANR-11-IDEX-0001-02 PSL* Research University). for KB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Fondation pour la Recherche sur le Cerveau (grant number AP FRC 2016). for KB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. City of Paris (grant number Grant Emergence 2014). for KB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Centre National de la Recherche Scientifique (grant number ATIP-Avenir (2014)). for KB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Fondation pour la Recherche Médicale (grant number). for SB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Université de Recherche Paris Sciences et Lettres (grant number). for SB. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

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