Neural basis for adolescent manic symptoms
medwireNews: Teenagers with subthreshold bipolar symptoms have altered structural connectivity in white matter (WM) tracts known to be involved in mood disorders, an imaging study shows.
"Our findings suggest widespread alterations in WM involving a number of tracts that continue to mature during adolescence," report Marie-Laure Paillère Martinot (Cochin Hospital, Paris, France) and team.
The study involved 42 adolescents (average age 14.6 years) with subthreshold bipolar symptoms, defined as having three manic symptoms on the Development and Well-Being Assessment (DAWBA) but not meeting the criteria for a psychiatric diagnosis.
Just 19% of these teenagers were at familial risk for a mood disorder, having a first- or second-degree relative with a history of depression or bipolar disorder (BD). Yet magnetic resonance imaging revealed significantly reduced fractional anisotrophy (ie, reduced WM bundle coherence) in one large cluster that encompassed many WM tracts reportedly affected in adolescents and adults with BD.
These tracts included the corpus callosum, the cingulum bundle, the superior and inferior longitudinal fasciculi, the uncinate fasciculus, the thalamic radiations, and the corticospinal tract. The changes were relative to findings in 126 age- and gender-matched adolescents without manic symptoms on the DAWBA, 21% of whom were also at familial risk for BD.
"Several WM bundles with significant WM alterations in this study are involved in the circuitry implicated in emotional regulation," the researchers note in Molecular Psychiatry. In particular, impairments in the cingulum bundle and the corpus callosum could "confer vulnerability to emotional dysregulation," they say.
A number of these tracts also had increased radial diffusivity in the adolescents with subthreshold bipolar symptoms relative to the controls.
The team believes the findings indicate that adolescents with bipolar symptoms "might be lagging 'behind' the controls in a number of WM bundles, notably in regions that develop faster than others in early adolescence."
In addition to the WM changes, adolescents with subthreshold bipolar symptoms also had significantly reduced gray matter (GM) volume in the left anterior cingulate, relative to the controls, and there was a trend toward reduced volume in the left medial frontal gyrus.
The cingulum bundle originates from these regions, observe the researchers. They say: "Smaller GM volume in those prefrontal regions, associated with delayed WM maturation in projecting bundles, might contribute to inadequate modulation of subcortical structures, and lead to mood dysregulation, which could underlie vulnerability to BD."
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By Eleanor McDermid, Senior medwireNews Reporter