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.
Gerald Edelman
Edelman's theory seeks to explain consciousness in terms of the morphology of the brain. A newborn baby's brain comprises a massive population of neurons (approx. 100 billion cells) and those that survive the initial phases of growth and development will make approximately 100 trillion connections with each other. A sample of brain tissue the size of a match head contains about a billion connections, and if we consider how these neuronal connections might be variously combined, the number of possible permutations becomes hyper-astronomical - in the order of ten followed by millions of zeros. The young brain contains many more neurons than will ultimately survive to maturity, and Edelman argued that this redundant capacity is needed because neurons are the only cells in the body that cannot be renewed and because only those cells and networks best adapted to their ultimate purpose will be selected as they organize into neuronal groups.