Bipolar I and II patients show abnormal white matter differences
MedWire News: Patients with bipolar I and bipolar II disorder have distinct neuropathological substrates, study findings show.
This is consistent with the heterogenous clinical presentations and cognitive functions previously seen in these patients, note the study researchers.
"The fiber alterations observed in the bipolar I patients were majorly associated with cognitive dysfunction, whereas those in the bipolar II patients were related to both cognitive and emotional processing," they report in the Journal of Affective Disorders.
Li-Fen Chen, from National Yang-Ming University in Taipei, Taiwan, and colleagues recruited 14 bipolar I disorder patients, 13 bipolar II disorder patients, and 21 mentally healthy individuals. They compared fractional anisotropy (FA) values calculated from diffusion tensor images among the groups.
Both groups of patients had lower FA values, indicating fiber impairments, in the thalamus, anterior cingulate, and inferior frontal areas, compared with controls.
The two patient groups differed, however, in that abnormal regions in bipolar II patients were more bilaterally distributed, extending to the left temporal lobe, whereas the fiber alterations of bipolar I patients were more lateralized to the right hemisphere.
Specifically, fiber alterations manifested in the thalamus and inferior frontal and rostral anterior cingulate areas in bipolar I patients but not bipolar II patients, while in bipolar II but not bipolar I patients, fiber alterations were evident in the temporal lobe.
Correlating these neuropathological findings with clinical characteristics, the researchers found that fiber alterations in the subgenual anterior cingulated cortices in both patient groups affected working memory performance.
The brain regions with significant fiber alterations in bipolar I patients are mainly related to cognitive functions.
The anterior cingulate cortex is highly involved in the network regulating both cognitive and emotional processing, with the rostral area, in particular, associated with monitoring of conflict or interference, decision making, and response to errors, the researchers explain. The thalamus is associated with the modulation of attentional processing and self-regulation of affective states, they add.
The brain areas with fiber deficits in the bipolar II patients are mainly associated with emotional processing. The bilateral subgenual anterior cingulated cortex is important in emotion regulation, the middle and inferior temporal areas are related to emotional appraisal processing, the middle temporal area modulates audiospatial information, and the right inferior frontal area is involved in emotional communicative processing based on facial emotions.
"Our results suggest that bipolar I and II patients present different neuropathological substrates in terms of the loss of bundle coherence of the disruption of fiber tracts," the researchers conclude.
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By Lucy Piper