The following is a summary of “Association Between the Fronto-Limbic Network and Cognitive and Emotional Functioning in Individuals With Bipolar Disorder,” published in the March 2023 issue of Psychiatry by Mesbah et al.
The cognitive and emotional functions of individuals with bipolar disorder (BD) are affected, and various brain circuits are implicated in BD, but they have not been studied in a meta-analysis of functional magnetic resonance imaging (fMRI) studies. For a study, researchers sought to compare the brain function of individuals with BD and healthy control individuals in emotion processing, reward processing, and working memory.
All fMRI experiments on BD published before March 2020 were included as data sources identified in PubMed, Embase, Web of Science, Cochrane Library, PsycInfo, Emcare, Academic Search Premier, and ScienceDirect literature search. The literature search was conducted on February 21, 2017, and March 2, 2020, and data were analyzed from January 2021 to January 2022. fMRI experiments comparing adult individuals with BD and healthy control individuals were selected if they reported whole-brain results and included a task assessing at least one of the domains. Out of 2,320 studies screened, 253 full-text articles were evaluated, and 49 studies were included after the selection procedure.
Coordinates that reported significant activation differences between individuals with BD and healthy control individuals were extracted, and differences in brain region activity were tested using the activation likelihood estimation method. The main outcome was a whole-brain meta-analysis that evaluated whether reported differences in brain activation in response to stimuli in the three cognitive domains between individuals with BD and healthy control individuals were different.
The meta-analysis included 999 individuals with BD (551 [55.2%] female) and 1027 healthy control individuals (532 [51.8%] female). Individuals with BD exhibited amygdala and hippocampal hyperactivity during emotion processing and hypoactivation in the inferior frontal gyrus (20 studies; 324 individuals with BD and 369 healthy control individuals). During reward processing, individuals with BD showed hyperactivation in the orbitofrontal cortex (9 studies; 195 individuals with BD and 213 healthy control individuals). Additionally, hyperactivation was found in the ventromedial prefrontal cortex and subgenual anterior cingulate cortex during working memory (20 studies; 530 individuals with BD and 417 healthy control individuals). The limbic hyperactivation was only present during euthymia in the emotion and reward processing domains. Moreover, abnormalities in frontal cortex activity were also found in individuals with BD experiencing mania and depression.
In conclusion, the meta-analysis revealed evidence of activity disturbances in the front-limbic network, specifically in key brain regions involved in cognitive and emotional processing in individuals with BD. The study suggested that aberrations in the fronto-limbic network may underlie cognitive and emotional dysfunctions in BD, present in both euthymic and symptomatic individuals.