Hedonic tone is associated with left supero-lateral medial forebrain bundle microstructure

Abstract

Background: The medial forebrain bundle (MFB) is an important pathway of the reward system. Two branches have been described using diffusion magnetic resonance imaging (MRI)-based tractography: the infero-medial MFB (imMFB) and the supero-lateral MFB (slMFB). Previous studies point to white-matter microstructural alterations of the slMFB in major depressive disorder (MDD) during acute episodes. To extend this finding, this study investigates whether white-matter microstructure is also altered in MDD patients that are in remission. Further, we explore associations between diffusion MRI-based metrics of white-matter microstructure of imMFB, slMFB and hedonic tone, the ability to derive pleasure.

Method: Eighteen remitted depressed (RD) and 22 never depressed (ND) participants underwent high angular resolution diffusion-weighted imaging (HARDI) scans. To reconstruct the two pathways of the MFB (imMFB and slMFB) we used the damped Richardson-Lucy (dRL) algorithm. Mean fractional anisotropy (FA) was sampled along the tracts.

Results: Mean FA of imMFB, slMFB and a comparison tract (the middle cerebellar peduncle) did not differ between ND and RD participants. Hedonic capacity correlated negatively with mean FA of the left slMFB, explaining 21% of the variance.

Conclusions: Diffusion MRI-based metrics of white-matter microstructure of the MFB in RD do not differ from ND. Hedonic capacity is associated with altered white-matter microstructure of the slMFB.

Keywords: white matter.

Fig. 1.

An individual example of the two reconstructed branches is shown for the left imMFB (yellow) and the left slMFB (red). Regions of interest are displayed in green.

Fig. 2.

The negative correlation across the whole sample between mean fractional anisotropy of the left slMFB and hedonic tone is displayed. ◇, Never depressed; ●, remitted depressed.