Monoaminergic modulation of emotional impact in the inferomedial prefrontal cortex.

People assess the impact of emotionally loaded images differently. We define impact as the average difference between individual ratings of standardized emotive images. To determine the neuroanatomical correlate of a hypothetical interaction between emotional impact and cerebral excitability, we first determined the individual effect on cerebral blood flow of a pharmacological challenge with the monoamine reuptake inhibitor clomipramine in nine healthy volunteers. We used regression analysis to identify sites in the ventromedial prefrontal cortex at which the two separately acquired measures, blood flow change and emotional impact of images, correlated significantly. The regression analysis identified a locus in Brodmann’s area 11 of the inferomedial prefrontal cortex at which the separate measures had significant inverse correlation. W e then tested the hypothesis that modulation of dopaminergic tone in patients with Parkinson’s disease would reveal the same site of reactivity in the ventromedial prefrontal cortex. We measured the changes of blood flow generated by deep brain stimulation of the subthalamic nucleus of the patients, and the changes correlated with the impact of the emotive images: In subjects with a low emotional impact, blood flow rose when the electrode was turned on, while in subjects of high impact, the flow to this site in the ventromedial prefrontal cortex declined when the electrode was turned on. Thus, under pharmacological or neurophysiological challenge, a key region of the inferomedial prefrontal cortex undergoes deactivation in proportion to the emotional impact of a stimulus.