Conclusion and future directions
Recent studies from human brain imaging and animal experiments have provided new insights into consciousness. Among several possible mechanisms, the thalamus projection to the brain is thought to be the core mechanism. Excitatory transmission and plasticity may play important roles in consciousness. Inhibitory transmission contributes to excitatory/inhibitory balance, thus, also controls consciousness. Studies using different experimental approaches reveal possible selective circuits (by optogenetic) and proteins (by gene manipulation and chemicals). From a basic research point of view, the future needs to reveal molecular and cellular mechanisms for the neuronal mechanism of consciousness. Animal experiments during anesthesia at least provide a good animal model for such studies. For clinical application, deep brain stimulation will only help to understand consciousness in humans, but also help patients with DOC. More importantly, how learning may affect the level of consciousness of human beings will be a vital question for neurons as well as society. Maybe that is an evolutionary force for human beings as well. High levels of consciousness due to constant brain learning may lead to prolonged life of the brain. Many brains decide to give up hope for life, at least in part, due to poor levels of consciousness during aging.