Brain Activity in Adolescent Major Depressive Disorder Before and After Fluoxetine Treatment

Twenty-three depressed adolescents (ages 11–17 years) were recruited for the study. While the majority (N=17) were recruited from the outpatient service, several (N=6) were recruited from ongoing treatment studies at the University of Texas Southwestern Medical Center/Children's Medical Center of Dallas. Depressed participants had a history of at least 4 weeks of nonpsychotic major depressive disorder based on DSM-IV criteria, with a score ≥4 on the Clinical Global Impressions severity subscale (CGI-S) (18) and a total score ≥40 on the Children's Depression Rating Scale–Revised (19). Patients with concurrent psychiatric disorders were allowed to participate as long as major depression was the primary disorder. Patients were excluded if they had a lifetime history of psychotic depression or bipolar disorders; substance abuse or dependence within the past 6 months; or treatment with psychotropic medications. Three patients withdrew consent before the first scan was conducted, and the imaging data for one participant were discarded because of excessive movement. Thus, analyzable baseline MRI data were available for 19 depressed adolescents. Of these, usable week 8 scans were available for 15 (three were not scanned at week 8, either because of worsening of depression or hospitalization [N=2] or because antidepressant treatment had been discontinued [N=1], and one scan was discarded because of excessive movement).

A total of 22 healthy adolescents (ages 11 to 18 years) were recruited from the community as comparison subjects; none had any current psychiatric illness, lifetime history of psychiatric illness, history of psychotropic medication use, or first-degree family history of psychiatric illness. The imaging data from one comparison subject were discarded because of excessive movement. Thus, usable baseline imaging data were available for 21 healthy comparison subjects. Of these, usable week 8 scans were available for 17 (two participants could not be scanned because they got braces, and one was no longer available after leaving for college; one scan was discarded because of excessive movement).

Adolescents recruited from the depression treatment studies were evaluated by the Schedule for Affective Disorders and Schizophrenia for School-Age Children–Present and Lifetime Version (20), and diagnoses were confirmed by a child psychiatrist. Clinical patients were diagnosed through clinical interviews and a checklist of DSM-IV's nine symptoms of major depressive disorder. Severity of depression was assessed by a child psychiatrist using the Children's Depression Rating Scale–Revised at baseline and at exit. Response to treatment was defined as a reduction of at least 50% on the total score on the Children's Depression Rating Scale–Revised at week 8 relative to baseline. The baseline scans were done within a week after evaluation. After the baseline scan, depressed adolescents started fluoxetine treatment as part of the treatment study protocol or as prescribed by their treating child psychiatrist (R.T. or G.J.E.). Treatment options were discussed with all participants before treatment was initiated. Fluoxetine was started at 10 mg/day, increased to 20 mg/day at week 2, and increased to 30–40 mg by week 8 as clinically indicated. Nonspecific psychotherapies (not cognitive-behavioral therapy or interpersonal therapy) were allowed to continue during fluoxetine treatment (two participants were in supportive therapy), although initiation of new therapy was not permitted during the study. All depressed participants were followed by a child psychiatrist in office visits (six visits for depression study patients and three visits for clinic patients) and telephone contact during the entire study. Depressed adolescents underwent scanning again 8 weeks after the initiation of fluoxetine treatment. Healthy comparison subjects were interviewed and scanned twice, 8 weeks apart.

The SPM5 software package (London, Wellcome Department of Imaging Neuroscience) was used to analyze the functional imaging data. Data were slice-time corrected for an interleaved bottom-up acquisition, adjusted for motion, and spatially normalized into a standard Montreal Neurological Institute (MNI) template. The image volume was then spatially smoothed with a 6-mm full width at half maximum Gaussian filter. Signal changes were modeled using the stimulation paradigm convolved with a canonical hemodynamic response function. Initial single-subject level analyses using a within-subject fixed-effects model were conducted to generate parametric maps for the three block conditions: neutral, fearful, and fixation. Results from the within-subject analyses were then used for subsequent second-level random-effects models.

Whole brain level t tests (two-sample and paired-sample) for the fearful > neutral contrast were conducted initially to guide subsequent region-of-interest analyses. Then a priori region-of-interest analyses were performed in regions of the amygdala, orbitofrontal cortex, and subgenual anterior cingulate cortex. Anatomic masks for the regions of interest were created using the automated anatomical labeling atlas (22) in the Wake Forest University PickAtlas utility (23). Activations within the regions of interest had to survive a small-volume correction at a threshold of p<0.05. Single-subject percent signal changes were then calculated using the MarsBaR toolbox in SPM5 (24). Functional masks for the amygdala were created using the voxels (five or more contiguous voxels) that showed a significant group-by-time interaction from the repeated-measures analysis of variance (ANOVA). Masks for the orbitofrontal cortex and the subgenual anterior cingulate cortex were created using voxels from the baseline two-sample t tests. The percent signal change calculation allowed us not only to verify the results from the SPM5 analyses but also to account for other covariates in the analyses (baseline activation, gender, age, depression severity, and so on) using SAS, version 9.2 (SAS Institute, Inc., Cary, N.C.). Thus, separate 2×2 (group-by-time) repeated-measures ANOVAs in SPM5 and a mixed linear model analysis of repeated measures with the Kenward-Roger correction applied to the unstructured covariance model in SAS were conducted to examine the differences in amygdala, orbitofrontal cortex, and subgenual anterior cingulate cortex activations between depressed adolescents and healthy comparison subjects for the fearful > neutral contrast over 8 weeks. Post hoc t tests in SPM5 and one-way ANOVAs or one-way analyses of covariance in SAS were conducted to evaluate the significant group-by-time interaction simple effects at baseline and at week 8, respectively. Additionally, mean changes in activation and the effect size of the change (Cohen's d) from baseline to week 8 for each region were examined using mean contrasts. Similar mixed-model analyses and post hoc tests of simple effects were also carried out with age, gender, and handedness included as covariates. To compare our results with those of previous studies, we also ran all analyses again, this time excluding patients with comorbid anxiety disorders from the depressed group (N=13 at baseline and N=9 at week 8).

Finally, baseline demographic and clinical differences between depressed and healthy adolescents were compared using two-independent-sample t tests, with the Satterthwaite method for unequal variances (for continuous variables) and Fisher's exact test (for categorical variables). The significance threshold for all tests was set at a p value of 0.05 (two-tailed); to address multiple testing on the post hoc tests of simple effects, p values were adjusted using the false discovery rate (25).

At baseline, the depression group showed significantly greater activations relative to the healthy comparison group for the fearful > neutral contrast in the regions of the left and right frontal lobe, temporal lobe, putamen, insula, and cingulate gyrus and in the right amygdala, right hippocampus, and right occipital cortex (p values, <0.001), although none of the differences reached a p value of 0.05 after false discovery rate correction for multiple testing. At week 8, the depression group had greater activation than the comparison group (in a single five-voxel cluster) only at the left superior and middle frontal gyrus (MNI coordinates: x=–25, y=44, z=4; z=3.66, t=4.16, uncorrected p<0.001; false discovery rate corrected p=0.76). See Table 2 for cluster size and MNI coordinates and Figure 2 for activation maps.