A functional viewpoint on paradoxical sleep-related brain regions.

Slow wave sleep is a condition for paradoxical sleep (PS) expression. The lower brain stem is able to produce the known PS phenomena but, in order to do so in all its functional magnitude, it depends on the rest of the brain. There are physiological conditions that appear as necessary to develop the PS. A group of basic functions, i.e., respiration, cardiovascular, brain oxygen availability, temperature, etc., have to go on in a non-homeostatic fashion during this state. Other conditions to be met are: the cut-off of the motor output and a different central control of the sensory input. During PS, phasic pO2 changes were observed in some nuclear structures characterized by a dramatic increase in the amplitude of oscillations. These changes were found in a number of subcortical, cerebellar and brain stem regions and were never observed neither in the neocortex, the specific thalamic nuclei nor in the white matter. It is postulated that these variations are due to a local increase in neuronal activity in PS during a decrease of the local homeostatic oxygen control. All the physiological changes above mentioned have a common anatomical denominator: the pons and medulla. Upon this region, proposed as the PS FINAL COMMON REGION, conveges rostral and caudal information making it the executor of all PS phenomena. The pons, on the other hand, has a bioelectrical activity of its own during PS, i.e., the ponto-geniculo-occipital spikes (PGO). This activity spreads through the brain and cerebellum. The cerebellum also participates in sleep physiology: the pO2 oscillations pattern and PGO are present in all of its parts, cortex and nuclei, being, the spike activity, dependent of a cholinergic pontine region. The pons shows a particular duality during PS. It is part of the FINAL COMMON REGION for PS phenomena and, at the same time, it is the origin of the PGO activity.