A new study has found that functional MRI (fMRI) may be the key for identification of specific neurons in the brain — called amygdala — which is vital in distinguishing bipolar (BP) disorder from depression, researchers report in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
Mayuresh Korgaonkar, Westmead Institute for Medical Research and the University of Sydney, and colleagues used sophisticated MRI scanning to see how the amygdala — a set of neurons that play a key role in processing emotions — reacts as a patient processes facial expressions such as anger, fear, sadness, disgust, and happiness.
The research showed that this key structure within the brain responds differently depending on whether the person has bipolar disorder or unipolar major depressive disorder (MDD). In people with bipolar disorder, the left side of the amygdala is less active and less connected with other parts of the brain than in people with depression.
The findings from this study had 80% accuracy in making this distinction.
The study holds importance as approximately 60% of patients with bipolar disorder are initially misdiagnosed as a major depressive disorder. Alarming, it can take up to a decade for these patients to be accurately diagnosed with bipolar disorder.
Bipolar disorder often first presents in the depressive phase of the illness and bipolar depression is similar to major depression in terms of clinical symptoms. Emotion processing is a core problem underlying both these disorders.
73 participants (23 BP and 25 MDD patients matched for age-gender, number of depressive episodes and severity; 25 age-gender matched healthy individuals) completed supra- and subliminal processing of threat, sad, happy and neutral faces during fMRI. Groups for activation and connectivity for the amygdala were then compared.
- BP participants had lower left amygdala activation than MDD during supraliminal and subliminal threat, sad and neutral processing and for subliminal happy faces.
- BP participants also exhibited lower amygdala connectivity to the insula and hippocampus for threat and to medial orbito-frontal for happy supraliminal and subliminal processing.
- BP participants also demonstrated greater amygdala-insula connectivity for sad supraliminal and subliminal face processing.
- Both patient groups were distinct from controls across several measures for activation and connectivity.
“Mental illness, particularly bipolar disorder and depression, can be difficult to diagnose as many conditions have similar symptoms,” Dr. Korgaonkar said. “These two illness are virtually identical except that in bipolar individuals also experience mania.
“This means distinguishing them can be difficult and presents a major clinical challenge as treatment varies considerably depending on the primary diagnosis. The wrong diagnosis can be dangerous, leading to poor social and economic outcomes for the patient as they undergo treatment for a completely different disorder.”
“Identifying brain markers that could reliably tell them apart would have immense clinical benefit.
“Such a marker could help us better understand both these disorders, identify risk factors for developing these disorders, and potentially enable clear diagnosis from early onset,” Dr. Korgaonkar said.
“Independent of valence or level of emotional awareness amygdala activation and connectivity during facial emotion processing can distinguish BP and MDD patients. These findings provide evidence that this neural substrate could be a potential trait-marker to differentiate these two disorders largely independent of illness state,” concluded the authors.
For further information log on to https://doi.org/10.1016/j.bpsc.2018.08.012
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