The utilization of the spinal toxin clearance route is regulated by thoracic pressure which changes during different sleep stages. The transfer of cranial soluble toxins to the spinal CSF occurs via the cranio-spinal CSF oscillation where a volume of CSF is displaced between the cranium and the spinal canal during each respiration cycle. The amplitude of the csCSF oscillation is inversely proportional to the amplitude of the thoracic expansion.