The fundamental role of sleep is the reduction of thermodynamic entropy of the central nervous system

Sleep remains the last major biological process for which a fundamental role is still unknown. Engagement and responsiveness to the environment are the main functions that are present during wakefulness and decreased during sleep and they generate a very important and unavoidable thing: entropy. It is our hypothesis that sleep is the process by which animals deal with the continuous increase in entropy generated by wakefulness and stated by the second law of thermodynamics. At a substratum level, this continuous increase in entropy, is associated with a higher number of microstates of the central nervous system (CNS) and threatens the high order that it needs to operate. The generation of entropy during wakefulness can be approached from two different, but related perspectives. First, from the point of view of metabolism and heat production in the CNS and second, from the perspective of the information that is received and processed from the environment. In humans, the brain uses approximately 20% of the energy available. Most neuronal processes are very energy-efficient but heat is still generated and entropy will increase. From a statistical mechanics and information theory perspectives, information received from the environment will inevitably increase the entropy of the system receiving it. The core concept of this hypothesis can be experimentally tested using current knowledge of CNS metabolism, thermodynamic principles, as well as concepts from the field of non-equilibrium thermodynamics.