Dopamine may well be the secret to what makes us human - meaning awfully bright, able to plan ahead, and resist impulses when it is necessary.
What is dopamine? It's a neurotransmitter, which means it controls communication in the brain. Dopamine can tell a neuron to fire off a signal or not, and modulates the signals. Dopamine is ancient - found in lizard brains and every other animal along the evolutionary tree up to Homo sapiens. But humans have a great deal of dopamine, and over many generations it seems we have evolved to have more and more.
Our prenatal neurochemical environment had a lot to do with how our dopamine machinery migrates and works in our brains. Which brings up an important point - one special thing about humans is our bipedalism. Being upright while mom is pregnant exposes our fetal brains to different environments than other primates, so the theory is this elevated the dopamine levels in the left hemisphere of most people's brains compared to other primates.
Humans also eat a lot of meat and fish compared to other primates - meat and fish give us more dopamine precursors. More dopamine is also associated with greater competitiveness, aggression, and impulse control - one could see how that particular combination of traits would be selected for over human evolution.
Serotonin, another neurotransmitter, is our oldest neurotransmitter and the original antioxidant - dopamine is what made humans so successful.
How do we get dopamine? We eat it. The precursor amino acid from the protein we eat is called tyrosine. Tyrosine becomes dopa via the enzyme tyrosine hydroxylase, and dopa becomes dopamine via the actions of dopa decarboxylase. (One more chemical reaction can turn dopamine into its best buddy neurotransmitter, norepinephrine, but more on that later). As is the case with serotonin and its precursor tryptophan, tyrosine can cross the blood brain barrier, but dopamine itself cannot. That means that the dopamine our brain needs must be manufactured from dopamine machinery and precursors in the brain.
What happens without dopamine, or with screwy dopamine machinery or inefficient dopamine? Well, in development this lack can cause mental retardation, which is the case in a rare genetic disease called PKU and cretinism (a type of mental retardation caused by iodine deficiency). Dopamine problems are implicated in ADHD, Alzheimer's, Parkinson's, depression, bipolar disorders, binge eating, addiction, gambling, and schizophrenia.
Having too much dopamine in the wrong place can make you psychotic. Illicit drugs that dump loads of dopamine include cocaine and methamphetamines. Therefore high amounts of dopamine can cause euphoria, aggression and intense sexual feelings.
When our dopamine machinery isn't working properly, problems ensue. Dopamine is linked to everything interesting about metabolism, evolution, and the brain. It is distributed quite differently on the different sides of the human brain, and it is speculated that this lateralization is responsible for how very human we are. The left brain (in almost all right-handed and most left-handed people) is responsible for language, linear reasoning, mathematics, that sort of thing, whereas the right side is usually responsible for intuition, holistic reasoning, some elements of music and speech intonation, etc.
If someone is young enough, half the brain can be scooped out and removed (if necessary, usually to control intractable seizures), leaving the child with pretty normal intellectual functioning (though motor functioning on one side is usually irrevocably lost).
The human brain has 100 billion neurons. Only 20,000 or so carry dopamine, and they do so in four major tracts. Dopamine is made in two little areas in the deep animal recesses of the brain - the substantia nigra and the ventral tegmental area. From these starting entrances, the dopamine areas reach out to various segments.
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