Elsevier

Biological Psychiatry

Volume 61, Issue 2, 15 January 2007, Pages 198-209
Biological Psychiatry

Original article
Increased Amygdala and Decreased Dorsolateral Prefrontal BOLD Responses in Unipolar Depression: Related and Independent Features

https://doi.org/10.1016/j.biopsych.2006.05.048Get rights and content

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.

Section snippets

Participants

Thirty patients with major depressive disorder and 28 healthy control subjects (no current or historical Axis I disorder via SCID [First et al 1996] diagnoses; demographics in Table 1) participated. Participants described no health problems, eye problems, or psychoactive drug abuse in the past 6 months. Participants with a history of psychosis, manic, or hypomanic episodes, or antidepressant use within 2 weeks of testing (6 weeks for fluoxetine) were excluded. Participants reported no excessive

Behavioral Data

Participants rated words consistent with their assigned categories, F(2,52) = 371.2, p < .005, η2 = .94, although depressed individuals rated positive words as less positive than control subjects, valence × group F(2,52) = 3.08, p = .05, η2 = .11 (Table 1). There were no main effects or interactions with group or valence on PRRT reaction times (p > .15).

There were no group or condition-related effects on reaction time for digit sorting; these were not expected because responses were to targets

Discussion

Unmedicated depressed and healthy individuals completed cognitive (digit sorting), and emotional (personal relevance rating of words) tasks. As in our previous study (Siegle et al 2002), depressed individuals displayed increased and sustained amygdala activity for up to 15 sec in response to briefly presented (250 msec) negative words compared with control subjects, who displayed little amygdala activity on the task. Depressed participants also displayed decreased DLPFC activity on both tasks.

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