In the Dopamine Primer 2, I covered the four major dopamine tracts in the brain. Today I'll break down the two most important ones to psychiatrists and anyone interested in the fabulous story of human evolution and greatness, the mesolimbic and the mesocortical pathways.
For simplicity sake (as mesolimbic and mesocortical don't have a whole lot of meaning unless you are versed in neuroanatomy, also because the mesolimbic system ends in the cortex so it is also mesocortical, and that's hella confusing), I'm going to call them the "medial" and "lateral" dopamine tracts respectively. The medial tracts go from the center, primitive, animal parts of the brain up to the emotional centers of the brain, and then to the front part of your brain (literally the center of your forehead, more or less). The lateral tracts go from the center, primitive, animal parts of the brain up around the outside and end up more by your eyeballs (more or less).
Both tracts carry dopamine, but the tracts are responsible for somewhat different human behaviors.
The lateral tracts are responsible for:
Future-orientation in predicting events
Rational, abstract thought
Focus and control
Someone who has an optimal amount of dopamine in the lateral system is going to be self-contained, practical, self-confident, and able to forgo immediate gratification in order to ensure greater reward later on. He or she might be the perfect person to bring with you on an expedition somewhere. However, an extreme "lateral dopamine" type person wouldn't be the one you might confide in with emotional problems. Also, on that expedition, if you break your leg and no longer become practical, it might be just a little too easy for he or she to leave your burdensome self there in the wilderness. So the dark side of dominant lateral tracts would be grandiosity, ruthlessness and sociopathy.
The medial tracts (more emotional in nature rather than rational thought) are responsible for:
Future-orientation in exploration (motivation and drive)
Creativity (along with paranormal experiences and psychosis)
Hyperactivity and impulsive behaviors
Euphoria and pleasure-seeking
A more medial dopamine personality might be a bit wacky, impulsive, and free-thinking. A hippie or an artist. Not particularly good at planning, but often compelling, creative and interesting. Maybe not the first person you would want to take into the wilderness, but perhaps capable of intuitive leaps of logic that could get you out of a real jam. And as it is the serotonin/norepinephrine right brain tracts that are more responsible for emotional sensitivity and understanding social cues, the medial dopamine dominant personality may not be particularly empathetic, and might wander off and leave you alone in the the wilderness as he or she might think of something better to do. The dark side of the medial dopamine dominance would be psychosis, paranoia and irresponsibility. (Keep in mind that these are all generalizations - all the tracts interact in complex ways so there is rarely any such thing as a pure "medial dopamine personality.")
Too much excess in the medial dopamine tracts leads to madness. Irrational thought, paranoia, loose thought associations, psychosis. In just enough excess it is creative genius. Families with schizophrenics are also more likely to have more creative individuals. And many people considered geniuses also suffered madness, such as Nobel Prize winner John Nash, a schizophrenic who had this to say when asked how a mathematician devoted to logic and proof could believe that extraterrestrials were sending him messages: "Because... the ideas I had about supernatural beings came to me the same way that my mathematical ideas did." Unfortunately, since schizophrenia is ultimately an inflammatory neurodegenerative disease, it is unlikely that a genius suffering from schizophrenia could maintain brilliance for more than a few adult decades.
It is an interesting observation of Previc's The Dopaminergic Mind in Human Evolution and History in that these two tracts seem to line up with Freud's separation of the human mind into the ego and the id (the id here being primitive drives of sex and pleasure-seeking, loose thought processes, and impulses of the medial dopamine tracts, whereas the ego weighs risks and benefits before jumping into any particular course of action - a lateral dopamine action. Freud's superego, or the conscience, is more likely more associated with those socially directed serotonin/norepinephrine right-brained tracts).
Estrogen has a tendency to inhibit dopamine (allowing for a greater dominance of social empathy, balance and those norepinephrine/serotonin pathways), whereas testosterone will tend to enhance dopamine. In the agricultural past, dopamine dominance has allowed for greatness and male dominance - Previc lists the following famous men in history and their "dopaminergic traits":
Alexander the Great - high intelligence, visionary, motivated, risk-taking, self-confident, but also grandiose, ruthless, restless, and paranoid.
Columbus - intelligent, visionary, motivated, self-confident, risk-taking, but also grandiose, ruthless, and restless.
Newton - extremely high intelligence, visionary, self-confident, motivated, but obsessive, lacking empathy and social skills, ruthless, paranoia, and neglected personal hygiene from time to time.
Napoleon - intelligent, visionary, motivated, risk-taking, self-confident, but with delusions of grandeur, ruthlessness, and restlessness.
Einstein - extremely high intelligence, visionary ideas, high motivation, self confidence, but had obsessiveness, lack of empathy and social skills, grandiosity, and personal hygiene neglect.
Which brings me to the present day, where is some respects things have flip-flopped between men and women, at least in America. According to a recent article in Time Magazine about the "Sheconomy," young single urban women outearn young single urban men, and while 35% of women aged 25-29 have a college degree, only 27% of men do. There is something going on (socially, in culture, environmentally? I could barely hazard a guess) that is making it easier for women to remain focused on long-term productive educational goals (a dopamine trait) in their youth. Women now own 1/3 of the businesses in America. As women still pay a major career penalty for having kids, and previous generations still control the Fortune 500, women have not cracked the higher echelons quite yet. But the Generation Y numbers could indicate that it is only a matter of time. And women still have the estrogen/serotonin/norepinephrine advantage of better being able to read social cues, which is an a helpful trait in sales, business, and even politics if coupled with enough grandiosity.
In an agricultural world, vision, ruthlessness and sociopathy allowed for one man to grab all power at the expense of his neighbors, creating kings. In a post-industrial world, the hyperdopamine advantage may not be quite so simple.