Mental illness, particularly bipolar disorder and depression, can be difficult to diagnose as many conditions have similar symptoms.  These two illnesses are virtually identical except individuals with bipolar disorder also experience mania.  The wrong diagnosis can be dangerous, leading to poor outcomes for the patient as they undergo treatment for the incorrect disorder, therefore identifying brain markers to reliably tell them apart would have immense clinical benefit.  Now, a study from researchers led by the Westmead Institute for Medical Research shows neurons deep inside the brain could hold the key to accurately diagnosing and differentiating bipolar disorder and depression.  The team states such a marker could help to better understand both these disorders, identify risk factors for developing them, and potentially enable clear diagnosis from early onset.  The study is published in the journal Biological Psychiatry: Cognitive Neuroscience and NeuroImaging.

Previous studies show approximately sixty percent of patients with bipolar disorder are initially misdiagnosed as a major depressive disorder.  Alarmingly, in some cases, 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, with emotion processing a core problem underlying both these disorders.  The current study shows amygdala activation, and connectivity during facial emotion processing can help to distinguish bipolar and depressive disorder patients, independent of the level of emotional awareness.

The current study utilizes fMRI to investigate how the amygdala, a region in the brain that plays a key role in processing emotions, reacts as seventy-three participants process facial expressions such as anger, fear, sadness, disgust, and happiness.  Results show the amygdala responds differently depending on whether the person has bipolar disorder or depression.  Data findings show 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, with 80% accuracy in making this distinction.

Results show bipolar disorder participants had lower left amygdala activation than patients with depression during tests involving a perceived and subconscious threat, sad and neutral processing, and for subconscious processing of happy faces. Data findings show bipolar disorder participants also exhibit lower amygdala connectivity to the insula and hippocampus for threat and less connectivity to the medial orbitofrontal for happy perceived and subconscious processing. The lab observed bipolar disorder participants also demonstrated greater amygdala-insula connectivity for perceived and subconscious sad facial processing in tests.

The team surmises their findings provide evidence the amygdala could be a potential trait-marker to differentiate bipolar disorder and depression largely independent of illness or emotional state.  For the future, the researchers state they are now running phase 2 of this study, which aims to further characterize these identified markers in a larger cohort of patients.

Source: Westmead Institute for Medical Research

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