ABSTRACT
Key research related to consciousness is that which investigates the neural systems that are deactivated or attenuated during altered states of consciousness, as well as during unconsciousness. This paper addresses various states of altered consciousness such as anaesthesia; sleep; vegetative states, seizures, post-LSD hallucinations, the minimally conscious state, locked-in syndrome, comatose states and thalamocortical dysrhythmia. Anaesthetics have been shown to act at all levels of integration in the central nervous system, with a wide range of known targets. Various conflicting theories regarding the anaesthetic state exist and a few are examined in this paper. In general, studies into altered states of consciousness emphasize the central role of prefrontal activity, the diffuse brain connectivity and the participation of the thalamocortical system/reticular formation in the maintenance of consciousness