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The Somatic Connection  |   May 2014
Mechanical Changes of the Brain During Sleep Clear Metabolites and Provide Key Mechanism for Sutherland's Cranial Respiratory Impulse
Author Affiliations
  • Hollis H. King, DO, PhD
    University of Wisconsin School of Medicine and Public Health, Madison
  • Nicholas C. Madaffer, DO
    Physical Medicine and Rehabilitation Resident, University of Wisconsin School of Medicine and Public Health, Madison
Article Information
The Somatic Connection   |   May 2014
Mechanical Changes of the Brain During Sleep Clear Metabolites and Provide Key Mechanism for Sutherland's Cranial Respiratory Impulse
The Journal of the American Osteopathic Association, May 2014, Vol. 114, 407-408. doi:10.7556/jaoa.2014.084
The Journal of the American Osteopathic Association, May 2014, Vol. 114, 407-408. doi:10.7556/jaoa.2014.084
Web of Science® Times Cited: 4
Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373-377. doi:10.1126/science.1241224.  
Sleep has long been a quandary for scientists, as it is required to sustain regular neurologic functioning yet its homeostatic mechanisms of action on the central nervous system have remained largely a mystery.1,2 Lacking a lymphatic system, the human brain was historically thought to secrete waste products via the choroid plexus, with waste products being absorbed by the arachnoid villi. This theory was proven incorrect, however, by the characterization of the glymphatic system.3 Using advanced imaging techniques (discussed previously in “The Somatic Connection”4), researchers have elucidated a key mechanism that is responsible for metabolite clearance from the brain in adult mice. Mechanical changes of the glymphatic system, and more specifically changes to the interstitial space volume (ISV), have been observed during sleep. 
Researchers from the Center for Translational Neuromedicine at the University of Rochester Medical Center in New York have furthered the understanding of metabolite clearance from the brain using quantitative in vivo 2-photon imaging and tetramethylammonium (TMA) diffusion changes via iontophoresis. Mice were studied using fluorescent and radiolabeled tracers, TMA, and β-amyloid (Aβ) infusion into the subarachnoid cerebral spinal fluid in the cortex during 3 states of wakefulness. Mice were awake, anesthetized, or sleeping; states of wakefulness were quantified by means of electrocorticography and electromyography recordings to monitor brain activity. 
The methodologic details and results are too numerous and complex to describe in the present review, but the salient clinical points were (1) a 60% increase in the ISV was measured during sleep states (either induced by anesthesia or naturally occurring), (2) the sleep-wake cycle itself is responsible for ISV changes, and (3) adrenergic signaling largely contributes to the alterations of neuronal activity in the sleep-wake cycle and the interstitial fluid.4 
Cranial osteopathic manipulative medicine has previously demonstrated alteration of the Baroarterial pulse waves (Traube-Hering-Mayer waves), which are responsible for the influx of cerebrospinal fluid inward along periarterial spaces.4-6 The study by Xie et al demonstrates that different states of wakefulness alter ISV and therefore fluid mechanics within the cranial vault. The phenomena encompassing cranial osteopathic manipulative medicine, as described by William Garner Sutherland, DO, are (1) the inherent motility of the central nervous system, (2) the articular mobility of the cranial bones, (3) the involuntary movement of the sacrum between the ilia, (4) the function of the reciprocal tension membrane, and (5) the fluctuation of the cerebral spinal fluid. These phenomena may be rooted in the neurologic, anatomic, and physiologic principles of ISV fluctuation, as sleep-wake (adrenergic) cycle fluctuations are typically noted during cranial osteopathic manipulative medicine.4,7,8 
References
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