Abnormal speech production in veterans with bipolar disorder: Relationship to the arcuate fasciculus

Individuals with bipolar disorder (BD) often present with language abnormalities, but few studies have quantified these features or examined their relationship with white matter microstructure.

We analyzed language samples from 17 Veterans with BD and 15 healthy Veteran controls elicited with an open-ended prompt about a stressful interpersonal experience. We applied singular value decomposition (SVD) to 275 linguistic features to derive low-dimensional component scores capturing the dominant covariance structure. In parallel, we conducted feature-level between-group tests and entered features showing nominal group differences (p < .05, uncorrected) into an exploratory principal components analysis (PCA) with oblique rotation to derive interpretable components. Neurite orientation dispersion and density imaging (NODDI) was used to characterize intracellular and extracellular microstructural properties within a mask of the arcuate fasciculus.

SVD revealed a significant group difference on the first component (p = .03). Feature-level analyses identified 16 variables showing group differences. PCA of these features yielded four interpretable components: (1) model predictability and present focus, (2) agency and directedness, (3) central concept connectedness, and (4) lexical and grammatical complexity, together explaining 75% of the variance. Within the BD group, lower scores on the first component were associated with greater neurite orientation dispersion in the arcuate fasciculus.

Cross-sectional design, small sample size, and lack of correction for multiple comparisons.

Preliminary findings indicate quantifiable language abnormalities in Veterans with BD and suggest links to altered dispersion of axons and dendrites in language-associated tracts.