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SLEEP LIKE A….
PEOPLE HAVE BEEN “sleeping like a log” since the 16th century, or at least they’ve been using this phase to describe it. We and other animals tend to combine sleep and immobility (with the exception of USWS types (unihemispherical slow-wave sleepers) and somnambulists (sleep-walkers).
“The Stillness of Sleep,” by William Wisden and Nicholas P. Franks, describes this sleep and immobility in Science magazine, January 24, 2020. The authors summarize a recent paper, “A Common Hub for Sleep and Motor Control in the Substania Nigra,” by Danqian Liu et al. published in this same issue of Science. Here are tidbits gleaned from these two articles, together with a bit of Internet sleuthing.
An International Study. Danqian Liu is at the University of California, Berkeley, in its Division of Neurobiology, Department of Molecular and Cell Biology, Helen Wils Neuroscience Institute, Howard Hughes Medical Institute. Twelve other colleagues are there; or at the National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences; or at the Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology.
Mouse Monitoring. The researchers monitored mice brain activity through electroencephalography (EEG), muscle activity through electromyography (EMG), and mobility through video recordings. Four states were identified with different levels of brain arousal and motor activity: locomotion, non-locomotive movement, quiet wakefulness, and sleep.
This and the following image are from Science, January 24, 2020.
Non-locomotive movement included eating, grooming, and adjustments of posture. Immobility was split between quiet wakefulness and sleep. And sleep had two components: an initial period of NREM (non-rapid-eye-movement) followed by an REM phase.
“Almost all transitions,” researchers noted, “occurred between adjacent states; for example, direct transitions from LM to SL or from MV to SL were never observed.”
The SNr and Brainstem. As noted by Wisden and Franks, the researchers found that “entering NREM sleep and stopping movement are wired together in mice. This is controlled by a brain region called the substantia nigra pars reticulata (SNr), which was thought to control motor actions only when mice are awake.”
What’s more, Wisden and Franks note, “The neural circuitry that suppresses movement during REM sleep seems entirely different from the circuit that suppresses movement in NREM sleep. During REM sleep, brainstem circuits actively suppress motor neurons in the spinal cord, which control skeletal muscle contractions.”
In mice, SNr neurons trigger both immobility and NREM sleep. A parallel circuit, located in the brainstem, imposes muscle atonia during REM sleep.
More To Sleep On. Wisden and Franks write, “… indeed, sleep researchers are still puzzled as to why two states of sleep exist.”
Now that the SNr’s contribution is more fully understood, other questions arise: What of dolphins, swifts, mallard ducks, and others that practice unihemispheric sleep? With half their brains still active, these animals apparently possess additional control circuits.
Also, might this SNr knowledge be put to use with enhanced anesthesia and selective targeting of sedatives?
Amina sleepwalking in Vincenzo Bellini’s La Sonnambula, 1831.
And what of somnambulists such as Amina or Lady MacBeth? ds
© Dennis Simanaitis, SimanaitisSays.com, 2020
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