Effects of manic episodes on the brain in bipolar disorder
Bipolar disorder is associated with cortical and subcortical structural brain abnormalities. Nevertheless, whether these abnormalities change gradually in time, and its correlation with the number of the manic-depressive states observed in bipolar disorder are not clear.
The biggest longitudinal brain imaging (MRI) study in its field to this date, which was carried out by the researchers in the Karolinska Institute in Sweden and the University of Gothenburg, sheds light on this question.
The data of this study, the results of which were published in the journal named Biological Psychiatry, were obtained from the ENIGMA Bipolar Disorder Working Group having a number of centers all around the world. 307 patients diagnosed with bipolar disorder, and 925 healthy control elements, aged between 23-57, were included in the study.
Using the magnetic resonance imaging method, measurements were made on the cerebral cortex thickness, surface area, and the areas beneath cerebral cortex. This analysis was repeated a year later to calculate the rates of change in the relevant regions. The results were compared between the bipolar group and the healthy group. Moreover, an analysis was carried out regarding the correlation of the manic-depressive episodes experienced and the rates of change in between the two time slots.
Changes in the Prefrontal Region
The researchers found a correlation between the number of manic episodes in bipolar patients and the severity of the cortical brain changes during the period of time concerning the research. While more manic episodes were correlated with a faster cortical thinning, no changes or increments were observed in the cortical thickness of the patients who did not experience any episodes. These changes were mostly apparent in prefrontal cortex, which is the center for emotion regulation, planning, decision-making, impulse control, and other significant cognitive functions.
Prof. Mikael Landén of the Institute of Neuroscience and Physiology, one of the authors of the study, said “It highlights the importance of the treatment in the prevention of mood episodes following the manic period-related cortical thinning in bipolar patients.”
Changes in Subcortical Regions
When the bipolar disorder patients were compared to healthy individuals, the changes that occurred in time showed significant differences in three brain regions: Ventricles that produce the cerebrospinal fluid which is critical for the protection of the brain, along with hippocampus that is related to facial recognition and memory, and the fusiform region.
While bipolar patients showed a faster expansion in the brain ventricles compared to the healthy control group, they showed a slower thinning on average in the fusiform and parahippocampal regions.
Bipolar Disorder is a Neuro-progressive Disorder
Christoph Abé, head author of the study, interpreted the changes in the subcortical regions by saying “Abnormal ventricular expansions, and most importantly, the correlations between the cortical thinning and manic symptoms indicate that bipolar disorder is in fact a neuro-progressive disorder. This, in turn, may explain the worsening of the bipolar symptoms in some patients.
Points to Take into Account: Effects of the Treatment
As bipolar disorder patients generally show a lower cortical thickness compared to healthy individuals, researchers emphasize that this may be related to the slow cortical thinning finding in the study. On the other hand, another possible explanation states that this finding may be stemming from treatment effects like the neuroprotective effects that are attributed to the lithium medication, and that the brain-related changes observed in this study, if left untreated, may not be the changes that occur during the natural course of the bipolar disorder.
– Abé, C., Ching, C. R., Liberg, B., Lebedev, A. V., Agartz, I., Akudjedu, T. N., … & ENIGMA Bipolar Disorder Working Group. (2021). Longitudinal structural brain changes in bipolar disorder: A multicenter neuroimaging study of 1,232 individuals by the ENIGMA Bipolar Disorder Working Group. Biological Psychiatry.