...an experiment created a freakish strain of laboratory mouse that lacks all motivation to eat... is physically capable of eating, likes the taste of food in its mouth, it will chew and swallow, all the while wriggling its nose in apparent rodent satisfaction if fed. Yet left on its own, the mouse will not rouse itself ... with overwhelming apathy... Days pass, the mouse doesn’t eat, it hardly moves, and within a couple of weeks, it has starved itself to death.
Behind the rodent’s fatal case of ennui is a severe deficit of dopamine, one of the essential signaling molecules in the brain. Dopamine has lately become quite fashionable, today’s “it” neurotransmitter, just as serotonin was “it” in the Prozac-laced ’90s.
“dopamine rush” — anything that imparts a small, pleasurable thrill. Familiar agents of vice like cocaine, methamphetamine, alcohol and nicotine are known to stimulate the brain’s dopamine circuits, as do increasingly popular stimulants like Adderall and Ritalin.
In the communal imagination, dopamine is about rewards, and feeling good, and wanting to feel good again, and if you don’t watch out, you’ll be hooked, a slave to the pleasure coursing through your brain.
Yet as new research on dopamine-deficient mice and other studies reveal, the image of dopamine as about pleasure transmission in the brain is misleading.
In the emerging view, dopamine is less about pleasure and reward than about drive and motivation, about figuring out what you have to do to survive and then doing it... the gasping for oxygen and the wolfing down of food when starved, shows the dopamine pathways of the brain are at full throttle. The whole brain is of one mindset the intense drive to get you out of a state of deprivation and keep you alive.
Dopamine is also part of the brain’s salience filter, its get-a-load-of-this device. “You can’t pay attention to everything, but you want to be adept as an organism at recognizing things that are novel,” Dr. Volkow said. “You might not notice a fly in the room, but if that fly was fluorescent, your dopamine cells would fire.”
In addition, our dopamine-driven salience detector will focus on familiar objects that we have imbued with high value, both positive and negative: objects we want and objects we fear. Dopamine makes a relevant object almost impossible to ignore.
There is also dopamine activity in the prefrontal cortex, the great executive brain. An impoverishment of prefrontal dopamine is thought to contribute to schizophrenia.
Scientists say that ADHD may be the result of reduced dopamine levels in the brain. Dopamine does many things in the brain, and plays important roles in behavior and thinking, attention, learning, motor activity, regulation of milk production, motivation and reward, sleep, and mood. This brain chemical is very important in the ADHD symptoms of hyperactivity, attention, motor activity, and the tendency to substance abuse.
What has been found is that the ADHD subjects have much lower levels of dopamine than their healthy counterparts. This was also true in parts of the limbic system, which controls emotional responses and memory.
People differ from one another at every juncture of the dopamine matrix, in the tonal background pace at which their dopamine neurons rhythmically fire, the avidity with which the cells spike in response to need or news, and the ease with which hyperstimulated cells revert to baseline.
Some researchers have looked at genetic variations in receptor types for clues to personality differences. According to Dan T. A. Eisenberg of Northwestern University, scientists have detected a modest connection between a relatively elongated version of dopamine receptor No. 4 and a tendency toward impulsivity and risk-taking behavior, particularly financial risk-taking... preliminary correlations in behavioral genetics ...
Source: NYT online
By NATALIE ANGIER
Yin And Yang
Balance
