Brain
There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. Serotonin, for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei. Norepinephrine, which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus. Other neurotransmitters such as acetylcholine and dopamine have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.
Eight-circuit model of consciousness
The Eight-Circuit Model of Consciousness is a hypothesis by Timothy Leary, and later expanded on by Robert Anton Wilson and Antero Alli, that "suggested eight periods [circuits] and twenty-four stages of neurological evolution". The eight circuits, or eight "brains" as referred by other authors, operate within the human nervous system, each corresponding to its own imprint and direct experience of reality. Leary and Alli include three stages for each circuit that details developmental points for each level of consciousness.
The first four circuits deal with life on earth, and survival of the species. The last four circuits are post-terrestrial, and deal with the evolution of the species, altered states of consciousness, enlightenment, mystical experiences, psychedelic states of mind, and psychic abilities. The proposal suggests that these altered states of consciousness are recently realized, but not widely utilized. Leary describes the first four as "larval circuits", necessary for surviving and functioning in a terrestrial human society, and proposed that the post terrestrial circuits will be useful for future humans who, through a predetermined script, continue to act on their urge to migrate to outer space and live extra-terrestrially. Leary, Wilson, and Alli have written about the idea in depth, and have explored and attempted to define how each circuit operates, both in the lives of individual people and in societies and civilization.