: An explanation of consciousness is one of the major unsolved problems of modern science. The modern view of consciousness arose in the nineteenth century; the view presumed that mental activity correlates with distinct physical states. Is the problem of consciousness real? Crick and Koch made a tentative assumption that all different aspects of consciousness (pain, seeing, thinking, emotion, self-consciousness) are connected by a basic common mechanism. The next step towards understanding involved the neuronal theories of consciousness (correlates of consciousness), often referred as the NNC (neural correlates of consciousness). Many neuroscientists presume that consciousness must have a neuronal correlate. The neuroscience of anaesthesia can be defined as studying the effect of anaesthetic agents on consciousness and the preconsciousness brain mechanisms of cognitive function. Some of these mechanisms, such as recognition of the novel stimuli, are still present in deep anaesthesia, during continuous suppression. Anaesthesia is not "an all or nothing" phenomenon and consciousness awareness with explicit memory represents only one part of the spectrum of cognitive functions. The introduction of safe general anaesthesia represents one of the most important, although under-appreciated, advances in modern surgery. There is some difficulty in defining the term "consciousness" in relation to the anaesthetic state. The difference in brain activity between those under anaesthesia and those not under any such influence.