Increased amygdala and decreased dorsolateral prefrontal BOLD responses in unipolar depression: related and independent features.

BACKGROUND: Major depressive disorder is characterized by increased and sustained emotional reactivity, which has been linked to sustained amygdala activity. It is also characterized by disruptions in executive control, linked to abnormal dorsolateral prefrontal cortex (DLPFC) function. These mechanisms have been hypothesized to interact in depression. This study explored relationships between amygdala and DLPFC activity during emotional and cognitive information processing in unipolar depression.

METHOD: Twenty-seven unmedicated patients with DSM-IV unipolar major depressive disorder and 25 never-depressed healthy control subjects completed tasks requiring executive control (digit sorting) and emotional information processing (personal relevance rating of words) during event-related functional magnetic resonance imaging (fMRI) assessment.

RESULTS: Relative to control subjects, depressed subjects displayed sustained amygdala reactivity on the emotional tasks and decreased DLPFC activity on the digit-sorting task. Decreased relationships between the time-series of amygdala and DLPFC activity were observed within tasks in depression, but different depressed individuals showed each type of bias.

CONCLUSIONS: Depression is associated with increased limbic activity in response to emotional information processing and decreased DLPFC activity in response to cognitive tasks though these may reflect separate mechanisms. Depressed individuals also display decreased relationships between amygdala and DLPFC activity, potentially signifying decreased functional relationships among these structures.