Anhedonia, defined as a diminished interest in or ability to experience pleasure, is associated with alterations of the neural circuitry of reward. In bipolar disorder (BD), results from whole-brain structural imaging studies suggest widespread white matter abnormalities (WM). The microstructure of WM tracts can be investigated using diffusion-weighted imaging (DWI), a technique that quantifies the restricted diffusion of water in WM through scalars, such as fractional anisotropy (FA), which indicates the directionality and coherence of WM bundles. In previous meta-analyses, reduced FA in the anterior corpus callosum and cingulum bundle have emerged as the most robust findings in individuals with BD (Favre et al., 2019). More recently, anhedonia in BD has been linked to changes in the uncinate fasciculus (UF) and superior longitudinal fasciculus (SLF, Diaz et al., 2022).The UF, a WM tract connecting the ventral prefrontal cortex and the amygdala is thought to play a crucial role in emotion regulation including symptoms of anhedonia (Versace et al., 2018). The SLF bilaterally is important for a multitude of cognitive functions and behaviours, including executive functioning and emotional regulation (Versace et al., 2018). Despite advancements in the field, the biological underpinnings of anhedonia is limited and only one study to date has investigated the association between anhedonia and white matter microstructure in patients with BD. Further, WM tract changes in BD have been inconsistent likely reflecting differences in patient characteristics and mood rating scales. The present study aims to extend previous work by investigating the relationship between white matter alterations and anhedonia using a validated measure the Snaith–Hamilton Pleasure Scale (SHAPS) in an already collected sample of BD (n= 50) and healthy (n= 50) participants. It is hypothesised that anhedonia will be associated with lower FA in the UF and SLF tracts.
