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Yurgelun-Todd, Deborah

The two halves of the brain are believed to play different roles in emotional processing, but the specific contribution of each hemisphere continues to be debated. The right-hemisphere hypothesis suggests that the right cerebrum is dominant for processing all emotions regardless of affective valence, whereas the valence specific hypothesis posits that the left hemisphere is specialized for processing positive affect while the right hemisphere is specialized for negative affect. Here, healthy participants viewed two split visual-field facial affect perception tasks during functional magnetic resonance imaging, one presenting chimeric happy faces (i.e. half happy/half neutral) and the other presenting identical sad chimera (i.e. half sad/half neutral), each masked immediately by a neutral face. Results suggest that the posterior right hemisphere is generically activated during non-conscious emotional face perception regardless of affective valence, although greater activation is produced by negative facial cues. The posterior left hemisphere was generally less activated by emotional faces, but also appeared to recruit bilateral anterior brain regions in a valence-specific manner. Findings suggest simultaneous operation of aspects of both hypotheses, suggesting that these two rival theories may not actually be in opposition, but may instead reflect different facets of a complex distributed emotion processing system.

People vulnerable to depression are at increased risk of relapse if they live in highly critical family environments. To explore this link, we used neuroimaging methods to examine cortico-limbic responding to personal criticisms in healthy participants and participants with known vulnerability to major depression. Healthy controls and fully recovered participants with a past history of major depression were scanned while they heard praising, critical, and neutral comments from their own mothers. Prior to scanning, the formerly depressed and the control participants were indistinguishable with respect to self-reported positive, negative, or anxious mood. They also reported similar mood changes after being praised or criticized. However, formerly depressed participants responded to criticism with greater activation in the amygdala and less activation in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) than did controls. During praise and neutral commentary, amygdala activation was comparable in both groups, although lower levels of activation in the DLPFC and ACC still characterized formerly depressed participants. Vulnerability to depression may be associated with abnormalities in cortico-limbic activation that are independent of mood state and that remain even after full recovery. Criticism may be a risk factor for relapse because it activates the amygdala and perturbs the affective circuitry that underlies depression.