Anticipations of Dopamine

Dopamine is famous for two things: 1. When it is depleted from the substantia nigra, it can cause Parkinson's disease 2. It is popularly thought of as the "pleasure neurotransmitter". It is also well known for being involved in schizophrenia.

Two new studies cast an interesting light on dopamine's variable effects -- depending upon the individual's genetic complement:

Highly creative person's have dompamine systems similar to schizophrenics.

"The study shows that highly creative people who did well on the divergent tests had a lower density of D2 receptors in the thalamus than less creative people," says Dr Ullén. "Schizophrenics are also known to have low D2 density in this part of the brain, suggesting a cause of the link between mental illness and creativity."

The thalamus serves as a kind of relay centre, filtering information before it reaches areas of the cortex, which is responsible, amongst other things, for cognition and reasoning.
"Fewer D2 receptors in the thalamus probably means a lower degree of signal filtering, and thus a higher flow of information from the thalamus," says Dr Ullén, and explains that this could a possible mechanism behind the ability of healthy highly creative people to see numerous uncommon connections in a problem-solving situation and the bizarre associations found in the mentally ill. _SD

This suggests that creative people are born and not made. But creativity is also a skill that can be improved in virtually anyone with practise. The higher realms of creativity may be reserved, however, for those with a combination of very high IQ and a genetic predisposition to creativity via brain structure.

Another fascinating finding relating to dopamine: Some people are genetically predisposed to have a strong dopamine response to drinking alcohol.

Using human positron emission tomography (PET), an imaging technique that allowed the researchers to analyze dopamine activity in the brain, they compared dopamine release in two groups of people that had been given a dose of alcohol. The groups consisted of those who carried a copy of the gene for the 118G mu-opioid receptor variant, and those who carried only genes for the more common 118A variant. They found that only people with the 118G variant had a dopamine response to alcohol -- no such response happened in subjects with the 118A receptor variant. _SD

The authors of the study suggest that persons with the 118G mu-opioid receptor variant may experience an enhanced pleasurable reaction to alcohol, predisposing to a greater risk of addiction.

Dopamine is not really a pleasure neurotransmitter -- it is more of an "anticipation of pleasure" neurotransmitter. It helps motivate the animal or person in pursuit of anticipated pleasure. Thus the connection of dopamine to addictions.

Another interesting line of research on the dopamine system involves the use of apomorphine to "kick-start" the dopamine system in vegetative patients.

One reason Fridman chose apomorphine was that it reaches dopamine receptors directly, even if the body's own ability to make the neurotransmitter is damaged. Apomorphine also binds to many types of dopamine receptors. Some other drugs, such as levodopa (L-dopa), are actually precursors—they are converted into dopamine by the body rather than acting directly on the receptors, so if that conversion mechanism were impaired they would be less helpful. Other drugs, such as amantadine, boost cellular production of dopamine, but if those cells are damaged or less active then they can only be boosted so far. Yet others only bind to certain dopamine receptors. _SciAm

Dopamine and Reward Seeking Behavior PDF

The dopamine reward circuit

The Dopamine System (short learning videos)

Dopamine by itself does not control behaviour. The neurotransmitter acts within the complex anatomy, physiology, biochemistry, and genetics of each individual brain. But humans tend to think in narratives, assigning each neurotransmitter its particular "role" to play, as if it were an independent actor.

Humans are constrained by such metaphorical thoughtways, and are often led down dead end streets of investigation. Perhaps the greatest challenge in learning about the universe around us, is rising above our own limitations in as many ways as we can.