Motor control during sleep and wakefulness: clarifying controversies and resolving paradoxes

Data accumulated during the last 40 years, since the discovery that there is a loss of muscle tone during REM sleep, have delineated many of the neurotransmitter systems, synaptic mechanisms and neuronal circuitries involved in the control of somatic motoneurons during sleep and waking states. Nevertheless, there are still a number of extant controversies as well as paradoxical and conflicting data. For example, the paradoxical modulation of motor activity that occurs in individuals with cataplexy during wakefulness compared to REM sleep is unresolved as are the mechanisms that are responsible for the control of hypoglossal motoneurons during normal states and those that are operative during sleep disorders such as obstructive sleep apnea. In addition, the circuitry whereby the hypocretinergic system promotes motor activation during wakefulness, and motor inhibition during REM sleep, has yet to be clarified. The use of new techniques, such those involving optogenetics and nanoparticles, will help to clarify the preceding issues and provide as a foundation for addressing a number of current critical unanswered questions such as those dealing with the differential control of motor activity in newborns and the aged. The resulting data will strengthen the foundation for the development of efficacious therapeutics to treat disorders of motor control that occur during sleep as well as wakefulness.