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Ungurean G, Rattenborg NC. A mammal and bird's-eye-view of the pupil during sleep and wakefulness. Eur J Neurosci 2024; 59:584-594. [PMID: 37038095 DOI: 10.1111/ejn.15983] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 03/03/2023] [Accepted: 03/30/2023] [Indexed: 04/12/2023]
Abstract
Besides regulating the amount of light that reaches the retina, fluctuations in pupil size also occur in isoluminant conditions during accommodation, during movement and in relation to cognitive workload, attention and emotion. Recent studies in mammals and birds revealed that the pupils are also highly dynamic in the dark during sleep. However, despite exhibiting similar sleep states (rapid eye movement [REM] and non-REM [NREM] sleep), wake and sleep state-dependent changes in pupil size are opposite between mammals and birds, due in part to differences in the type (striated vs. smooth) and control of the iris muscles. Given the link between pupil dynamics and cognitive processes occurring during wakefulness, sleep-related changes in pupil size might indicate when related processes are occurring during sleep. Moreover, the divergent pupillary behaviour observed between mammals and birds raises the possibility that changes in pupil size in birds are a readout of processes not reflected in the mammalian pupil.
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Affiliation(s)
- Gianina Ungurean
- Max Planck Institute for Biological Intelligence, Seewiesen, Germany
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Ungurean G, Behroozi M, Böger L, Helluy X, Libourel PA, Güntürkün O, Rattenborg NC. Wide-spread brain activation and reduced CSF flow during avian REM sleep. Nat Commun 2023; 14:3259. [PMID: 37277328 DOI: 10.1038/s41467-023-38669-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Accepted: 05/03/2023] [Indexed: 06/07/2023] Open
Abstract
Mammalian sleep has been implicated in maintaining a healthy extracellular environment in the brain. During wakefulness, neuronal activity leads to the accumulation of toxic proteins, which the glymphatic system is thought to clear by flushing cerebral spinal fluid (CSF) through the brain. In mice, this process occurs during non-rapid eye movement (NREM) sleep. In humans, ventricular CSF flow has also been shown to increase during NREM sleep, as visualized using functional magnetic resonance imaging (fMRI). The link between sleep and CSF flow has not been studied in birds before. Using fMRI of naturally sleeping pigeons, we show that REM sleep, a paradoxical state with wake-like brain activity, is accompanied by the activation of brain regions involved in processing visual information, including optic flow during flight. We further demonstrate that ventricular CSF flow increases during NREM sleep, relative to wakefulness, but drops sharply during REM sleep. Consequently, functions linked to brain activation during REM sleep might come at the expense of waste clearance during NREM sleep.
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Affiliation(s)
- Gianina Ungurean
- Avian Sleep Group, Max Planck Institute for Biological Intelligence, Seewiesen, Germany.
| | - Mehdi Behroozi
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr-University Bochum, Bochum, Germany.
| | - Leonard Böger
- Max-Planck Research Group Neural Information Flow, Max Planck Institute for the Neurobiology of Behavior - caesar, Bonn, Germany
- Max-Planck Research Group Genetics of Behaviour, Max Planck Institute for the Neurobiology of Behavior - caesar, Bonn, Germany
| | - Xavier Helluy
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr-University Bochum, Bochum, Germany
- Department of Neurophysiology, Medical Faculty, Ruhr-University Bochum, Bochum, Germany
| | - Paul-Antoine Libourel
- CRNL, SLEEP Team, UMR 5292 CNRS/U1028 INSERM, Université Claude Bernard Lyon 1, Lyon, Bron, France
| | - Onur Güntürkün
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr-University Bochum, Bochum, Germany
- Research Center One Health Ruhr, Research Alliance Ruhr, Ruhr-University Bochum, Bochum, Germany
| | - Niels C Rattenborg
- Avian Sleep Group, Max Planck Institute for Biological Intelligence, Seewiesen, Germany
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Pupil Dynamics-derived Sleep Stage Classification of a Head-fixed Mouse Using a Recurrent Neural Network. Keio J Med 2023. [PMID: 36740272 DOI: 10.2302/kjm.2022-0020-oa] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The standard method for sleep state classification is thresholding the amplitudes of electroencephalography (EEG) and electromyography (EMG) data, followed by manual correction by an expert. Although popular, this method has some shortcomings: (1) the time-consuming manual correction by human experts is sometimes a bottleneck hindering sleep studies, (2) EEG electrodes on the skull interfere with wide-field imaging of the cortical activity of a head-fixed mouse under a microscope, (3) invasive surgery to fix the electrodes on the thin mouse skull risks brain tissue injury, and (4) metal electrodes for EEG and EMG recording are difficult to apply to some experimental apparatus such as that for functional magnetic resonance imaging. To overcome these shortcomings, we propose a pupil dynamics-based vigilance state classification method for a head-fixed mouse using a long short-term memory (LSTM) model, a variant of a recurrent neural network, for multi-class labeling of NREM, REM, and WAKE states. For supervisory hypnography, EEG and EMG recording were performed on head-fixed mice. This setup was combined with left eye pupillometry using a USB camera and a markerless tracking toolbox, DeepLabCut. Our open-source LSTM model with feature inputs of pupil diameter, pupil location, pupil velocity, and eyelid opening for 10 s at a 10 Hz sampling rate achieved vigilance state estimation with a higher classification performance (macro F1 score, 0.77; accuracy, 86%) than a feed-forward neural network. Findings from a diverse range of pupillary dynamics implied possible subdivision of the vigilance states defined by EEG and EMG. Pupil dynamics-based hypnography can expand the scope of alternatives for sleep stage scoring of head-fixed mice.
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Rattenborg NC, Ungurean G. The evolution and diversification of sleep. Trends Ecol Evol 2023; 38:156-170. [PMID: 36411158 DOI: 10.1016/j.tree.2022.10.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 10/17/2022] [Accepted: 10/24/2022] [Indexed: 11/19/2022]
Abstract
The evolutionary origins of sleep and its sub-states, rapid eye movement (REM) and non-REM (NREM) sleep, found in mammals and birds, remain a mystery. Although the discovery of a single type of sleep in jellyfish suggests that sleep evolved much earlier than previously thought, it is unclear when and why sleep diversified into multiple types of sleep. Intriguingly, multiple types of sleep have recently been found in animals ranging from non-avian reptiles to arthropods to cephalopods. Although there are similarities between these states and those found in mammals and birds, notable differences also exist. The diversity in the way sleep is expressed confounds attempts to trace the evolution of sleep states, but also serves as a rich resource for exploring the functions of sleep.
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Affiliation(s)
- Niels C Rattenborg
- Max Planck Institute for Biological Intelligence (in foundation), Seewiesen, Germany.
| | - Gianina Ungurean
- Max Planck Institute for Biological Intelligence (in foundation), Seewiesen, Germany
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Abstract
Since the discovery of rapid eye movement (REM) sleep, the nature of the eye movements that characterize this sleep phase has remained elusive. Do they reveal gaze shifts in the virtual environment of dreams or simply reflect random brainstem activity? We harnessed the head direction (HD) system of the mouse thalamus, a neuronal population whose activity reports, in awake mice, their actual HD as they explore their environment and, in sleeping mice, their virtual HD. We discovered that the direction and amplitude of rapid eye movements during REM sleep reveal the direction and amplitude of the ongoing changes in virtual HD. Thus, rapid eye movements disclose gaze shifts in the virtual world of REM sleep, thereby providing a window into the cognitive processes of the sleeping brain.
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Affiliation(s)
- Yuta Senzai
- Department of Physiology, University of California, San Francisco, San Francisco, CA, USA
- Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA, USA
| | - Massimo Scanziani
- Department of Physiology, University of California, San Francisco, San Francisco, CA, USA
- Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA, USA
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Žunkovič B, Schmidt M. Sleep: The great adaptive diversity. Curr Biol 2021; 31:R1527-R1530. [PMID: 34875243 DOI: 10.1016/j.cub.2021.10.055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
A new study shows that bird pupillary responses during sleep are opposite to those seen in mammals, findings that expand our understanding of the great adaptive diversity of sleep and the expression of its components across species.
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Affiliation(s)
- Breda Žunkovič
- Clinical Institute for Clinical Neurophysiology, University Medical Center Ljubljana, Ljubljana, Slovenia
| | - Markus Schmidt
- Department of Neurology, Center for Experimental Neurology, Bern University Hospital (Inselspital) and University, Bern, Switzerland; Ohio Sleep Medicine Institute, 4975 Bradenton Avenue, Dublin, OH 43017, USA.
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