Tract-specific white matter structural disruption in patients with bipolar disorder

Area of Science:

• Neuroscience
• Psychiatry
• Medical Imaging

Background:

• Mood disorders like major depressive disorder (MDD) and bipolar disorder (BD) are linked to emotional and cognitive network dysfunction.
• Brain network abnormalities, beyond localized lesions, are increasingly implicated in mood disorders.

Purpose of the Study:

• To quantify structural injury in white matter (WM) connections of the emotional network using diffusion tensor (DT) tractography.
• To investigate structural differences in the limbic network between patients with MDD, BD, and healthy controls.

Main Methods:

• Acquired conventional and DT magnetic resonance imaging (MRI) brain scans from 15 MDD patients, 15 BD patients, and 21 healthy controls.
• Utilized FSL software to measure diffusivity changes in WM fiber bundles of the emotional network.
• Focused on connections between the amygdala and regions including the cingulate cortex, parahippocampal cortex, orbitofrontal cortex, dorsolateral prefrontal cortex, and insula.

Main Results:

• Bipolar disorder patients exhibited significantly decreased fractional anisotropy and increased mean, axial, and radial diffusivity in anterior limbic network WM fiber bundles compared to controls and MDD patients.
• These diffusivity changes were observed in most WM fiber bundles connecting limbic structures.
• Lithium medication was associated with normalized diffusivity in tracts connecting the amygdala and subgenual cingulate cortex.

Conclusions:

• Detected specific WM abnormalities indicating disrupted fiber bundle integrity in bipolar disorder (BD) patients.
• These findings may elucidate mood dysregulation and cognitive deficits in BD.
• WM abnormalities could serve as objective markers for monitoring treatment efficacy in BD.