Sleep and Dreaming

Who’s up for a brief discussion on the science of the sleep process? Although I’ve studied dreams and dreaming for more than three decades and have blogged and published on the nature and evolution of the dreaming brain, I consider myself merely well informed rather than expert on the topic. However, based on the most recent and available peer-reviewed research, I will be making some definitive statements about the nature of sleep and dreaming that you may find compelling, if not informative. First, let’s explore why we sleep and dispel some misconceptions about why we dream and remain immobile while dreaming.

Definitively, sleep and dreaming primarily serves the metabolic demands of our active brain and any mental benefit we experience after a cycle of sleep and dreaming is merely a byproduct of the metabolic processes our brain engages amid the sleep process--which includes dreaming. Sleep is a neurological imperative caused by the extracellular accumulation of adenosine, a hypnogenic molecule, in the brain. Adenosine accumulates as the brain metabolizes its primary source of energy, the sugar adenosine triphosphate (ATP). Adenosine build-up triggers a cascade of neural effects that induce the initial stage of sleep, non-REM (NREM). As NREM progresses, adenosine, beta amyloids (a peptide), and other extracellular waste are flushed from the brain via a hydraulic or convection system of waste removal dubbed the glymphatic system. Thus NREM, the initial stage of sleep, clears our brain of potential toxins, which prepares our brain for wakeful activity.

The wakeful activity our brain normally engages after NREM is dreaming (REM). Dreaming is another way of describing those episodes of increased activity our sleeping brain experiences relative to its NREM sleep stages. Again, we dream to serve our brain’s metabolic demands and serving those demands enhances our mental acuity and overall brain function. Research shows that the sleep process increases the level of glycogen in the brain. Glycogen is the reserve form of the ATP and oxygen our brain stores to meet the emergent energy demands of conscious activity not immediately supplied or satisfied through normal cerebral blood flow. At the end of each cycle of NREM, our brain activates to resupply its glycogen reserves. That activation increases blood flow to those brain areas with depleted glycogen reserves. REM is the neural effect of our brain acting to regenerate its reserve energy supply. The imagery and content of our dreams are how our brain synthesizes the lingering neural affects that this energy storage process causes. With its toxins removed and energy reserves resupplied, our brain functions better and is prepared for full arousal to consciousness.

Finally, we remain immobile while dreaming as a consequence of NREM rather than REM. Our lack of mobility while dreaming (atonia) initiates to serve the metabolic needs of the body at rest. Atonia is the inelastic state of muscle tone that our body experiences during the dreaming stages of sleep. This aspect of our muscle posture is mediated by neural structures below those associated dream production. It was the nineteenth century Nobel Laureate, Sir Charles Sherrington, who first observed how his low-decerebrate research animals would collapse into an atonic muscle posture when they were continually left undisturbed or unfed. Sir Sherrington was investigating the reflexive system of his test animals through the successive removal of brain structure. In 1963, the French sleep researcher Dr. Michel Jouvet, described this tonic-to-atonic cycle of behavior in his test animals as evidence of the “rhomencephalic phase of sleep.” If our brain retains evidence of its evolution path, then where atonia’s mediation arises--relative to other sleep components in brain structure--suggests that in its earliest incarnation atonia evolved between cycles of active survival behaviors where energy expense was minimal or unnecessary. During contemporary sleep, atonia punctuates the final stage of each cycle of NREM, which is the most passive, inactive state of normal brain function relative to dreaming and conscious brain function. We remain immobile while dreaming because our immobility conserves energy. Our brain is the largest consumer of our body’s energy uptake and our immobility amid sleep supports our dreaming brain’s efforts to resupply its energy reserves.

Because I am a new user, I am unable to post links to my sources (adenosine, ATP, glymphatic system, and glycogen). If you are interests in those sources, PM me and I will send you the links. I welcome your critique of my comment and I hope you are not discouraged by the science. The science also suggests that dreams are meaningful and I encourage your thoughts as to whether any of this suggests the opposite. I hope you have been informed.