Originally Posted by Emily Mattes
This cycle is a physiological explanation for why food can be such a psychological comfort . . . It would be interesting to compare the brain scans of a very obese person eating a candy bar with a heroin addict receiving an injection of methadone (as I highly doubt any research facility would be allowed to use tarballs!).
Good idea Emily! Thought you might be interested in a paper published yesterday on this very topic
(Stice et al., 2008; abstract below). It's been known for some time that obsese individuals have fewer dopamine receptors in a specific brain area (e.g., Wang et al. 2001
), which may be due to genentic predisposition or dopamine receptor downregulation. The paper by Stice et al. adds to this by showing that activity in this brain area in response to food (a chocolate milkshake) is blunted in overweight subjects, and is in fact negatively correlated with BMI across the subject pool (higher the BMI the more blunted the response).
Stice et al. (Science, Oct 17, 2008) abstract:
"The dorsal striatum plays a role in consummatory food reward, and striatal dopamine receptors are reduced in obese individuals, relative to lean individuals, which suggests that the striatum and dopaminergic signaling in the striatum may contribute to the development of obesity. Thus, we tested whether striatal activation in response to food intake is related to current and future increases in body mass and whether these relations are moderated by the presence of the A1 allele of the TaqIA restriction fragment length polymorphism, which is associated with dopamine D2 receptor (DRD2) gene binding in the striatum and compromised striatal dopamine signaling. Cross-sectional and prospective data from two functional magnetic resonance imaging studies support these hypotheses, which implies that individuals may overeat to compensate for a hypofunctioning dorsal striatum, particularly those with genetic polymorphisms thought to attenuate dopamine signaling in this region.