Thursday, May 19, 2011

Dr. Emily Dean - Dopamine, the Left Brain, Women, and Men

Via Dr. Emily Dean's Evolutionary Psychiatry blog at Psychology Today. In this post she outlines some brain-based differences in men and women that correlate with various forms of mental illness. For example, dopamine controls the left hemisphere, which tends to be dominant in men, and likewise, men tend to suffer more from autism, ADHD, schizophrenia, and addiction, all of which are dopamine mediated diseases.

She also speculates that neurotransmitter dominance may play a role in personality disorders (Axis II diagnoses). Men tend to be more likely to be diagnosed with antisocial personality disorder (sociopath/psychopath), which involves impulse control issues, aggression, substance abuse, and a lack of empathy - all of which are related to dopaminergic systems.

Conversely, many more women than men are diagnosed with borderline personality disorder, which involves extremes of emotions, boundary issues, and impulse control issues (among other things) - all of which are connected to serotonin and norepinephrine systems, as well as impulse control issues being related to poorly regulated dopaminergic systems. Men turn it outward toward others - women turn it inward toward themselves in the form of suicide and depression.

BUT . . . all of this is based on correlations in adults - there is no proven cause and effect. This could all be wrong, but it's the only explanation going right now that offers a medical treatment. Of course, we also know that therapy works, but it takes longer and costs more.

AND . . . who knows how much socialization wires the brain toward certain neurotransmitter patterns. Nurture must always be considered alongside nature in these issues.

Dopamine, the Left Brain, Women, and Men

How dopamine may influence gender differences in psychiatric disorders
Published on May 17, 2011 by Emily Deans, M.D. in Evolutionary Psychiatry.

In my last post on dopamine, I introduced this essential neurotransmitter and put forward some evidence that it is the key to the thinking style of humanity. Today we'll go over the different neurotransmitters on the different sides of the brain, and why it matters where we think.

Dopamine is the neurotransmitter that is not only responsible for modulating a lot of our physical movement, but also sex, aggression, motivational drive, and, counter-intuitively, long-term planning and restraint or impulse control. In nearly all right-handed and most left-handed humans who are left-brain dominant, dopamine rules the left side of the brain. Lateral dopamine pathways modulate working memory, cognitive shifting, and other executive functions (such as planning).

On the right side of the brain - the artsy part - serotonin and norepinephrine are more dominant. Serotonin and norepinephrine have more to do with emotional activation and arousal systems. The serotonin systems manage our movements and focus on a close personal level. They work in close concert with the opiate reward system and some other hormonal and neuronal systems associated with close in work - feeding babies, eating - stuff we would do with our gaze directed downward, and usually doesn't require as much planning. Norepinephrine and serotonin networks also manage our vestibular systems, helping us balance, postural control, and knowing which way is up or down. Again, one associates balance with looking down or being centered in space. Norepinephrine tracts in the brain are also heavily involved in the "close-in" sense of touch.

The dopamine systems on the left side of the brain become more active with thinking and planning that is more long term. Scanning the horizon, searching and recognition. These systems rarely operate close in our personal space, as it is rare to bring something within arm's reach that we do not already recognize. The medial dopamine systems are used in exploration, navigation, and orientation to landmarks. Far vision, upward gaze, hearing, and smell are more associated with the dopamine tracts. Dopamine's linkage to distant space seems to have associated itself in humans with distant time as well. There is no species quite so future oriented as Homo sapien. No other species has such high concentrations of dopamine in the brain.

An obvious and perhaps controversial correlate to these different neurotransmitter systems responsible for close/feeling/balance versus far/navigation/planning is the inherent female/male parallel. Aggressive "male" behaviors are mediated by dopamine, whereas receptive "female" and maternal behaviors (grooming, feeding) are mediated by close-in cues, norepinephrine, and opiate and oxytocin systems.

Psychiatrically speaking, it is probably not a coincidence that dopamine related disorders, such as schizophrenia, addiction, ADHD and autism are more common in men, whereas the serotonin/norepinephrine linked anxiety and depressive disorders are more common in women. Of course dopamine is also associated with depression and opiates with addiction, and men get depressed and anxious while women have ADHD and autism. These are obviously not absolutes, just trends.

I will speculate here that the differences in personality disorder diagnoses between men and women may relate to the neurotransmitter dominance differences as well. Many more men have the diagnosis of antisocial personality disorder than women - basically, a sociopath. A person with antisocial personality disorder generally lacks empathy for others, and often struggles with impulsivity and aggressive drives and substance abuse. That combination will get you sociopathic behavior - stealing, murder, etc.

On the other hand, many more women than men are diagnosed with borderline personality disorder. Someone who has borderline personality disorder generally has trouble with relationships and containing feelings appropriately. He or she can struggle with rage and impulsive behavior also, but often the violence is directed at him or herself in suicide attempts or self-injurious behavior. A person with borderline personality disorder has empathy but has trouble applying it - he or she likely has boundary issues and has a hard time sitting with another person's pain without feeling it too much as his or her own. Thus he or she will feel very deeply for someone, then when it gets to be too much, push him or her away. People with borderline traits also tend to have impulsive behavior and have higher risk for substance abuse. Both borderline and sociopathic individuals are likely to have experienced abuse or neglect as a child, but some have not and still have the disorder.

So if we run with the rather gross simplification that men are dopamine "left brain" dominant and women perhaps more balanced between the right and left hemispheres, you can see how troubles with regulating dopamine combined with an underactive social/empathy serotonin/norepinephrine system would get you sociopathy in a man. In a woman, the trouble in borderline personality seems to be more in the poor regulation of both - but perhaps more a deficiency of dopamine and a dysregulation of the social/empathy serotonin/norepinephrine side of things.

And, of course, there are borderline men and antisocial women (think Sharon Stone in "Basic Instinct"). It is an appropriate supposition that some of our social male/female constructs keep us from wanting to diagnose women with antisocial personalities, and perhaps the same social constructs, pressures, and expectations mean that an abused boy child has the risk of growing up into a sociopath, and an abused girl child has the risk of developing borderline personality disorder. I'm inclined to believe some of that is going on, but that the biology is also at play. Of course, many abused children grow up without having personality disorders at all.

I'll finish up with a discussion of how our brains end up the way they do in the first place. The same gravimetric serotonin-driven vestibular systems that help us stay balanced are responsible for the migration and localization of the dopamine tracts as they are formed in early development. The theory goes that our bipedalism keeps us oriented differently than other primates or other animals in utero, leading to different gravity signals and a more lateralized brain development (meaning our right and left brains are simply more different than the right and left brains of any other animals.). There are no known genes that act as master directors for this lateralization - it all seems to be related to epigenetic factors and serotonin availability in the right place at the right time.

Natural human movement, then, is what may make our brains human.

(Once again I'm drawing from Previc's The Dopaminergic Mind in Human Evolution and History). Also Previc's paper "The neuropsychology of 3-D space")

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More articles like this one at Evolutionary Psychiatry

Copyright Emily Deans, M.D.

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