Reduced interhemispheric resting-state functional connectivity in unmedicated bipolar II disorder

Area of Science:

• Neuroimaging
• Psychiatry
• Brain Connectivity

Background:

• Neuroimaging studies increasingly report altered structural and functional brain connectivity in bipolar disorder (BD).
• Changes in functional interactions between cerebral hemispheres in BD remain less understood.
• Interhemispheric functional connectivity is crucial for cognitive processes.

Purpose of the Study:

• To investigate interhemispheric functional connectivity in the whole brain of patients with bipolar II disorder (BD II) during a resting state.
• To identify specific brain regions with altered functional homotopy in BD II.

Main Methods:

• Resting-state functional magnetic resonance imaging (fMRI) was performed on 26 unmedicated BD II patients and 40 healthy controls.
• Voxel-mirrored homotopic connectivity (VMHC) was used to measure functional connectivity between symmetrical interhemispheric voxels.

Main Results:

• Patients with BD II exhibited significantly lower VMHC compared to controls in the medial prefrontal cortex and inferior temporal gyrus.
• No regions demonstrated increased VMHC in the BD II group.
• No significant correlations were found between VMHC values in affected regions and clinical symptom severity.

Conclusions:

• The findings indicate significant impairments in interhemispheric coordination in individuals with BD II.
• Reduced functional connectivity in specific cortical regions may underlie cognitive deficits in BD II.