Thursday, August 03, 2006

Personality Predicts Responsivity of the Brain Reward System

The Journal of Neuroscience has started a new feature: short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows. They are meant to mimic the journal clubs that exist in many academic department or institutions.

A recent entry by J. B. Engelmann discusses a paper by Beaver et al. that examines the relationship between a personality trait, reward sensitivity, and activity of the brain reward system measured by functional magnetic resonance imaging. A study like this is relevant to understanding the over-consumption of appetizing high-caloric foods that has contributed to the dramatic increase in obesity within the past 20 years, making obesity a top 10 global health threat. Here are some clips from the review and article:

Figure - A highly simplified schematic diagram outlines the connections between central nodes in the brain reward system (modified from Berridge and Robinson, 2003). Animal as well as human neuroimaging studies have implicated this network in the hedonic and motivational effects of natural rewards and drugs of abuse, such as food and amphetamine. AMYG, Amygdala; NAC, nucleus accumbens; OFC, orbitofrontal cortex; VP, ventral pallidum; VTA/SN, ventral tegmental area/substantia nigra.

Beaver et al. showed that reward sensitivity, as assessed by the Behavioral Inhibition Scale/Behavioral Activation Scale, predicted neural responses to pictures of appetizing foods in the network of the brain regions outlined in the Figure. Functional magnetic resonance imaging, in conjunction with a blocked experimental design, was used to record blood oxygenation-level dependent (BOLD) responses while participants passively viewed pictures of foods from four different categories...The authors found increased activation in orbitofrontal cortex (appetizing vs nonfood objects) and bilateral ventral striatum (appetizing vs bland foods). Interestingly, there was a dissociation between left and right orbitofrontal cortex such that appetizing food stimuli activated the left orbitofrontal cortex, whereas disgusting food stimuli activated the right orbitofrontal cortex.

Beaver et al. provide an important link between human behavioral research that has demonstrated an association between trait reward sensitivity and unhealthy eating habits and animal research implicating the reward network in hyperphagia and increased intake of high-caloric foods. Their findings thus offer a possible explanation for why some individuals overeat compulsively. It will be interesting to establish a more direct link between compulsive overeating and responsivity of the reward system, for instance by correlating activity in the reward system in response to images depicting appetizing foods and body mass index. Finally, an abundance of parallels between obesity and drug addiction points to similarities in the underlying brain mechanisms and neural adaptations that accompany these two conditions

1 comment:

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