Altered intrinsic functional connectivity in language-related brain regions in association with verbal memory performance in euthymic bipolar patients

Abstract

Potential abnormalities in the structure and function of the temporal lobes have been studied much less in bipolar disorder than in schizophrenia. This may not be justified because language-related symptoms, such as pressured speech and flight of ideas, and cognitive deficits in the domain of verbal memory are amongst the hallmark of bipolar disorder (BD), and contribution of temporal lobe dysfunction is therefore likely. In the current study, we examined resting-state functional connectivity (FC) between the auditory cortex (Heschl's gyrus [HG], planum temporale [PT]) and whole brain using seed correlation analysis in n = 21 BD euthymic patients and n = 20 matched healthy controls and associated it with verbal memory performance. In comparison to controls BD patients showed decreased functional connectivity between Heschl's gyrus and planum temporale and the left superior and middle temporal gyrus. Additionally, fronto-temporal functional connectivity with the right inferior frontal/precentral gyrus and the insula was increased in patients. Verbal episodic memory deficits in the investigated sample of BD patients and language-related symptoms might therefore be associated with a diminished FC within the auditory/temporal gyrus and a compensatory fronto-temporal pathway.

Figure 1

One-way ANCOVA of the functional connectivity scores (FC) with Group as between-subject factor and age, sex and education as covariates (ANCOVA F-map corrected for FDR and cluster size) and T-Tests of the group contrast controls (n = 20) vs. bipolar disorder (BD) patients (n = 21), cluster threshold: p < 0.05). The upper rows indicate the functional connectivity maps in the entire sample, the lower rows the group contrast. (A): Significant regions with bilateral Heschl’s Gyrus (HG) as seed-region. Colour code: red = positive FC. blue = negative FC. (B): Significant regions with bilateral planum temporale (PT) as seed-region. The left side in the figure indicates the right side of the brain (radiological convention). Colour code: red = CON > PAT. blue = PAT > CON.

Figure 2

Coefficients of functional connectivity (FC) of significant areas in the group comparisons of the seed-regions for BD patients (n = 21) and controls (n = 20). Upper rows (A): FC between bilateral Heschl’s Gyrus (HG) and left middle temporal gyrus. Lower rows (B, C): FC between bilateral planum temporale (PT) and right middle and superior and middle temporal gyrus and between bilateral PT and the right inferior frontal and precentral gyrus and right insula. red = patients < controls, blue = patients > controls. Vertical lines indicate the upper and lower quartiles, single points display outliners.