Investigators might have detected brain circuitry dysfunction in euthymic bipolar II patients, according to an imaging study published online in Progress in Neuro-Psychopharmacology & Biological Psychiatry.
The team compared functional MRIs of 19 adult patients euthymic for at least 2 weeks with 18 adult controls with no personal or family history of mental illness. The subjects ranged in age from 21 to 45. Participants with bipolar disorder scored significantly lower on the Wechsler Test of Adult Reading, which suggested that they had lower IQs and socioeconomic status. None of the study participants with bipolar disorder reported ever experiencing a manic or mixed episode, or catatonic symptoms.
On the day of the scan, the subjects’ mood and psychomotor symptoms were assessed using the Youth Mania Rating Scale for hypomanic symptoms, the Montgomery-Åsberg Depression Rating Scale for depressive symptoms, and the CORE for psychomotorsymptoms, reported Dr. William R. Marchand, a psychiatrist at the Veterans Affairs Medical Center in Salt Lake City, and his colleagues (Prog. Neuropsychopharmacol. Biol. Psychiatry. 2014 Jan. 16 [doi:10.1016/j.pnpbp.2014.01.004]).
"We found [statistically significant] increased functional connectivity among bipolar subjects compared to healthy controls in two [cortical midline structure] circuits," reported Dr. Marchand, who also is affiliated with the departments of psychiatry and psychology at the University of Utah. "One circuit included the medial aspect of the left superior frontal gyrus and the dorsolateral region of the left superior frontal gyrus. The other included the medial aspect of the right superior frontal gyrus, the dorsolateral region of the left superior frontal gyrus, and the right medial frontal gyrus and surrounding region."
Specifically, in the left medial superior frontal region, significantly increased connectivity was found (cluster size 628 voxels; P = .0008), compared with controls. In the dorsolateral region of the left superior frontal gyrus, in one cluster, the investigators also found significantly increased connectivity (cluster size 673 voxels; P = .0004) among the subjects with bipolar disorder, compared with controls.
The investigators said cortical midline structure (CMS) circuitry is thought to play a key role in the neurobiology of affective illness because the "medial cortex is involved in emotional regulation, self-referential thinking, the default mode network and may mediate the relationship between aberrant self-referential thinking and negative affect in mood disorders."
Previously, the investigators identified similar problems in depressed patients with bipolar disorder. That the problems persist even when patients are doing well indicates that the findings "may represent trait pathology." Among the implications, they said, is that "nonmedication approaches that impact medical cortical function, such as mindfulness-based interventions, may warrant evaluation as adjunctive treatments for relapse prevention."
One limitation of the study cited by the investigators is the relatively small sample size. They suggested that future studies focus on whether CMS circuits affect cognitive processes.
No financial disclosures were reported. The study was funded by the Department of Veterans Affairs.