Psy-World

Treatment with a selective serotonin reuptake inhibitor diminishes the neural processing of both rewarding and aversive stimuli.

Animal and human studies indicate that serotonin pathways exert an inhibitory influence over neural systems mediating both positive and negative affective processes. The ability of the selective serotonin reuptake inhibitors (SSRIs) to relieve symptoms of low energy, decreased motivation, and loss of pleasure (anhedonia) remains to be clarified. Using functional magnetic resonance imaging (fMRI) a study evaluated brain responses to reward-related and aversive stimuli in 45 healthy volunteers. The participants were randomized to receive short-term treatment (7 days) with the SSRI citalopram, the noradrenaline reuptake inhibitor reboxetine, or placebo in a double-blind between-groups design. On the final day of drug treatment fMRI explored neural responses to rewarding (sight and/or flavor of chocolate) and aversive stimuli (sight of mouldy strawberries and/or an unpleasant strawberry taste). Analysis of fMRI scans revealed that citalopram decreased activation to the chocolate stimuli in the ventral striatum and the ventral medial/orbitofrontal cortex, whereas reboxetine did not modify ventral striatal activity but increased neural responses within medial orbitofrontal cortex to reward. In addition citalopram reduced brain responses to the aversive stimuli in the lateral orbitofrontal cortex (LOFC) and insula, known to be “punishment” areas. Reboxetine produced a similar, although weaker effect, in LOFC. These results might explain the modest antidepressant efficacy of SSRIs in patients whose depression is characterized by loss of motivation and pleasure. Further studies are necessary to explore whether, in depressed patients, SSRI treatment may produce a different effect on the neural processing of reward than that seen in healthy volunteers. Ideally antidepressant would enhance neural responses to reward while diminishing responses to aversive stimuli. McCabe C, Mishor Z, Cowen PJ, Harmer CJ (2009). Diminished Neural Processing of Aversive and Rewarding Stimuli During Selective Serotonin Reuptake Inhibitor Treatment. Biol Psychiatry (in press). Updated January 2010