But when the researchers induced pain in the volunteers' jaw muscle, and asked them to rate different aspects of how they were feeling, differences emerged in specific sub-areas of the basal ganglia. For example, the more a person rated the pain as causing emotional distress and fear, the more dopamine was released in the area known as the nucleus accumbens ?the same region implicated in drug addiction.
That effect persisted even after the researchers controlled for the negative emotional effects caused by the actual research setup, which included a needle inserted into a large jaw muscle, and the expectation of pain and repeated questioning.
Similarly, dopamine release in two other areas of the basal ganglia ?the putamen and caudate nucleus ?was strongly correlated with the rating of how intense and unpleasant the pain itself was on a scale of 0 to 100. The authors concluded that in some areas of the basal ganglia, dopamine was involved in the assessment of pain itself, while in the ventral area, or nucleus accumbens, it was related to the emotional experience of pain.
The study used positron emission tomography, or PET, scanning that allowed the researchers to calculate the level of dopamine activity by measuring the percentage of dopamine receptors on the surface of brain cells that were active. To do this, they used the drug raclopride, to which had been attached a short-lived radioactive form of carbon. The drug binds to the same receptors that dopamine does, so the more of it that could be seen in a specific brain area, the less dopamine was present and vice versa.
The researchers also scanned each volunteer's brain using magnetic resonance imaging (MRI) in order to create
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Source:University of Michigan Health System