Subjects gave written informed consent to participate, as approved by the NIMH IRB. Participants met DSM-IV criteria for BD, most recent episode depressed, MDD in a current major depressive episode, MDD in full remission (RD) based on the structured clinical interview for the DSM-IV (SCID-IV)(19
) and an unstructured clinical interview with a psychiatrist. The following exclusion criteria applied: significant medical or neurological disorders, past head injury with loss of consciousness, significant risk of suicide, meeting DSM-IV criteria for substance abuse within the previous 6 months or substance dependence within the previous 5 years, pregnancy, general MRI exclusion criteria or electrolyte disturbance, anemia, or positive illicit drug or HIV screen on laboratory testing. Healthy control (HC) subjects (n=74) met the same exclusion criteria, had no lifetime history of a psychiatric disorder, and no first degree relative with a mood or anxiety disorder, as established using the Family Interview for Genetic Studies (FIGS)(20
The unmedicated BD group consisted of 22 subjects who had not been exposed to psychotropic medications at least 2 months prior to scanning. Of these patients, 8 were naïve to psychotropic drugs and the remaining 14 were unmedicated for an average of 86±103 (range 10 to 345) weeks. Unmedicated patients with BD had the following comorbid conditions: post-traumatic stress disorder (PTSD) and social phobia (n=2); generalized anxiety disorder (GAD) (n=2); social phobia and panic disorder (n=2); social phobia and bulimia nervosa (n=1), and social phobia and obsessive compulsive disorder (OCD) (n=1). Five unmedicated BD patients met criteria for alcohol abuse in the remote past. One unmedicated individual with BD had a remote history of cannabis dependence, and 1 individual had a remote history of alcohol dependence.
The medicated group (n=15) consisted of 8 cases taking lithium, 6 cases taking divalproex, and 1 case taking chlorpromazine (lithium and divalproex therapeutic blood levels documented within several days of scanning). The following comorbid conditions were recorded: panic disorder (n=1); OCD (n=1); PTSD and GAD (n=1), social phobia and PTSD (n=1); panic disorder, social phobia, and PTSD (n=2); bulimia nervosa (n=2); and social phobia and PTSD (n=1). Six medicated subjects with BD had a past history of alcohol abuse, and 1 patient had abused both cannabis and phencyclidine (PCP). Two medicated BD patients had a remote history of alcohol dependence.
All MDD (n=28) and RD (n=32) patients were either medication-naïve or were unmedicated for at least 4 weeks (6 for fluoxetine). One MDD patient had co-occurring OCD, and 3 had a history of alcohol abuse. Three patients with RD had a past history of alcohol abuse.
High-resolution anatomical images were acquired using a GE 3T MRI scanner; a standard head radiofrequency coil; and a magnetization-prepared, rapid gradient echo (MP-RAGE) pulse sequence: (echo time [TE]=2.1 msec, repetition time [TR]=7.8msec, prep time = 725 msec, delay time=1400 msec, flip angle=6°). One hundred twenty-four axial slices (slice thickness=0.6 mm) were acquired with a 14 cm field-of-view and in-plane resolution of 224×224 voxels, resampled to 256×256x124 voxels for reconstruction, resulting in a displayed resolution of 0.55×0.55×0.6 mm. Three to four 13 minute scans were consecutively acquired, coregistered, and summed to increase signal-to-noise ratio. To enhance the accuract of manual segmentation, prior to analysis the signal-to-noise ratio was increased by summing each two consecutive coronal planes to enhance the accuracy of manual segmentation.
A second MP-RAGE image of the entire brain also was acquired to measure whole brain volume (WBV) (TE=4.94msec; TR=11.6 msec, prep time=725 msec; delay time=1400msec, voxel size=0.85 × 0.85 × 1.2 mm).
The habenula was segmented by one rater (WB) blind to diagnosis, in each coronal plane in which this structure was seen bulging into the third ventricle along the ventromedial aspect of the thalamus or lying ventral and medial to the stria medullaris of the thalamus (; Mai et al. (21
)). The medial boundary was formed by the cerebrospinal fluid of the third ventricle, and the ventral boundary by the white matter of the posterior commissure. The dorsal and lateral borders were defined by the white matter of the stria medullaris of the thalamus in anterior planes or the mediodorsal thalamic nucleus, limitans nucleus or pretectal area in posterior planes (,(21
)). The inter-rater reliability scores for the segmentation of 10 images was assessed using an interrater correlation coefficient.
Figure 1 Coronal MRI sections showing the habenula and the local anatomical landmarks which enabled its segmentation. Because the habenular nuclei contain relatively dense white matter plexuses they can be collectively delimited from the gray matter of the adjacent (more ...)
Whole brain volume (WBV) was measured using an automated technique, as described previously(18
). Briefly, the FSL tool, FAST, was used to segment the whole brain image into gray matter, white matter and CSF images, after correcting for intensity nonuniformity using the minc tool, N3. The gray and white matter components then were summed to generate the WBV.
The a priori hypothesis that the habenula volume would be decreased bilaterally in depressed MDD subjects and unmedicated, depressed BD subjects versus healthy controls was tested by comparing absolute and normalized (absolute habenula volume ÷ WBV) volumes across groups. First, repeated measures ANOVAs with left versus right hemisphere as the within subjects factor was used to test for absolute and normalized habenula volume differences between the 3 groups (MDD, unmedicated BD and HC). Thereafter, independent sample t-tests were used to test the individual group contrasts except where demographic or clinical variables differed between diagnostic groups, in which case a general linear model with the appropriate covariates was used instead. In post hoc analyses aimed at addressing the specificity of the findings from these comparisons, the habenula volume of the medicated BD group was compared to the HC group using a general linear model, controlling for handedness and age. The RD group did not differ from the HC group in any demographic variable, and therefore the difference in habenula volumes between these 2 groups was compared using an independent sample t-test.
Finally, exploratory analyses were performed post hoc
to assess sex effects on the habenular volumes within the mood disorder samples, and to evaluate potential associations between habenular volumes and clinical parameters of age-at illness-onset, illness duration, time spent medication free, symptom severity, bipolar subtype (I versus II). BD I is characterized by episodes of major depression and mania while patients with BD II suffer from episodes of major depression and sub-threshold symptoms of mania, that is, hypomania(22