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Reduced white matter integrity and verbal fluency impairment in young adults with bipolar disorder: a diffusion
Isabelle E Bauer1, Austin Ouyang2, Benson Mwangi1
1University of Texas Health Science Center at Houston, Department of Psychiatry and Behavioral Sciences, 77054 Houston, TX, United States.
Background:
Clinical evidence shows that bipolar disorder (BD) is characterized by white matter (WM) microstructural abnormalities. However, little is known about the biological mechanisms associated with these abnormalities and their relationship with cognitive functioning.
Methods:
49 adult BD patients ((M±SD): 29.27 ± 7.92 years; 17 males, 32 females; 34 BD-I, 10 BD-II, and 5 BD-NOS) and 28 age-matched normal subjects ((M±SD): 29.19 ± 7.35 years; 10 males and 18 females) underwent diffusion tensor imaging (DTI) imaging. DTI metrics were computed using whole-brain tract-based spatial statistics (TBSS) as part of the FMRIB Software Library. Measures of WM coherence (fractional anisotropy - FA) and axonal structure (mean, axial and radial diffusivity - MD, AD and RD) were employed to characterize the microstructural alterations in the limbic, commissural, association and projection fiber tracts. All participants performed the Brief Assessment of Cognition for Affective disorders (BAC-A).
Results:
BD patients performed poorly on verbal fluency tasks and exhibited large clusters of altered FA, RD and MD values within the retrolenticular part of the internal capsule, the superior and anterior corona radiata, and the corpus callosum. Increased FA values in the left IFOF and the forceps minor correlated positively with verbal fluency scores. Altered RD parameters in the corticospinal tract and the forceps minor were associated with reduced visuomotor abilities.
Conclusions:
The reported verbal fluency deficits and FA, RD and MD alterations in WM structures are potential cognitive and neural markers of BD. Abnormal RD values may be associated with progressive demyelination.
Insights
Bipolar disorder (BD) is linked to white matter (WM) abnormalities, affecting cognitive functions like verbal fluency. Diffusion tensor imaging revealed specific WM alterations associated with these cognitive deficits in BD patients.
Area of Science:
- Neuroimaging
- Psychiatry
- Cognitive Neuroscience
Background:
- Bipolar disorder (BD) is clinically associated with white matter (WM) microstructural abnormalities.
- The biological mechanisms underlying these WM changes and their impact on cognition remain unclear.
Purpose of the Study:
- To investigate WM microstructural alterations in bipolar disorder patients using diffusion tensor imaging (DTI).
- To explore the relationship between these WM abnormalities and cognitive functioning in BD.
Main Methods:
- 49 adult BD patients and 28 healthy controls underwent DTI.
- Tract-based spatial statistics (TBSS) analyzed WM coherence (fractional anisotropy - FA) and axonal integrity (mean, axial, radial diffusivity - MD, AD, RD).
- Cognitive performance was assessed using the Brief Assessment of Cognition for Affective disorders (BAC-A).
Main Results:
- BD patients showed poorer verbal fluency and altered FA, RD, and MD values in specific WM tracts, including the internal capsule and corpus callosum.
- Increased FA in the left inferior fronto-occipital fasciculus (IFOF) and forceps minor correlated with better verbal fluency.
- Altered RD in the corticospinal tract and forceps minor was linked to reduced visuomotor abilities.
Conclusions:
- WM microstructural alterations (FA, RD, MD) and verbal fluency deficits may serve as neural and cognitive markers for BD.
- Abnormal radial diffusivity (RD) suggests potential demyelination contributing to cognitive impairments in bipolar disorder.
