Distinguishing between depression in bipolar disorder and unipolar depression using magnetic resonance imaging: a systematic review

Abstract

Objectives: Magnetic resonance imaging (MRI) studies comparing bipolar and unipolar depression characterize pathophysiological differences between these conditions. However, it is difficult to interpret the current literature due to differences in MRI modalities, analysis methods, and study designs. Methods:We conducted a systematic review of publications using MRI to compare individuals with bipolar and unipolar depression. We grouped studies according to MRI modality and task design. Within the discussion, we critically evaluated and summarized the functional MRI research and then further complemented these findings by reviewing the structural MRI literature. Results:We identified 88 MRI publications comparing participants with bipolar depression and unipolar depressive disorder. Compared to individuals with unipolar depression, participants with bipolar disorder exhibited heightened function, increased within network connectivity, and reduced grey matter volume in salience and central executive network brain regions. Group differences in default mode network function were less consistent but more closely associated with depressive symptoms in participants with unipolar depression but distractibility in bipolar depression. Conclusions:When comparing mood disorder groups, the neuroimaging evidence suggests that individuals with bipolar disorder are more influenced by emotional and sensory processing when responding to their environment. In contrast, depressive symptoms and neurofunctional response to emotional stimuli were more closely associated with reduced central executive function and less adaptive cognitive control of emotionally oriented brain regions in unipolar depression. Researchers now need to replicate and refine network-level trends in these heterogeneous mood disorders and further characterize MRI markers associated with early disease onset, progression, and recovery.

Neurochemical and microstructural alterations in bipolar and depressive disorders: A multimodal magnetic resonance imaging study

“…Because distinguishing BD from UD solely based on clinical clues is difficult, other promising neural markers are being explored using neuroimaging measures, and non-invasive functional magnetic resonance imaging (MRI) has produced promising results (2,3). Non-invasive in vivo measures of brain structure and function derived from MRI have shed light on the underlying brain alterations associated with BD.…”

Subjects with bipolar disorder showed different reward system activation than subjects with major depressive disorder in the monetary incentive delay task

“…This means that a high reward condition might be associated with both positive and negative arousal in our paradigm. Recent review article about distinguishing between dBD and dMDD showed that activity of salience network (one of the functional brain networks which includes AI, ACC and thalamus) in dBD subjects were more unstable and susceptible to emotional stimulation than dMDD subjects 38 . In the current study, dBD subjects may have been more affected by the negative aspect of high reward, and AI activity was more increased compared to rBD subjects or dMDD subjects.…”

Experiences that matter in bipolar disorder: a qualitative study using the capability, comfort and calm framework

“…Better understanding the patient's experience of misdiagnosis could strengthen providers' ability to build trust with patients. In the longer term, biomarkers and risk factors that might more clearly differentiate bipolar disorder from other conditions need continued development and direct clinical application to improve diagnosis and treatment (Rowland and Marwaha 2018;Siegel-Ramsay et al 2021).…”