Background. Mood instability and risk-taking are hallmarks of borderline personality
disorder (BPD). Schema modes are combinations of self-reflective evaluations, negative
emotional states, and destructive coping strategies common in BPD. When activated,
they can push patients with BPD into emotional turmoil and a dissociative state of
mind. Our knowledge of the underlying neurocognitive mechanisms driving these changes
is incomplete. We hypothesized that in patients with BPD, affective instability is
more influenced by reward expectation, outcomes, and reward prediction errors (RPEs)
during risky decision-making than in healthy controls. Additionally, we expected that
these alterations would be related to schema modes. Methods. Thirty-two patients with
BPD and thirty-one healthy controls were recruited. We used an established behavioral
paradigm to measure mood fluctuations during risky decision-making. The impact of
expectations and RPEs on momentary mood was quantified by a computational model, and
its parameters were estimated with hierarchical Bayesian analysis. Model parameters
were compared using High-Density Intervals. Results. We found that model parameters
capturing the influence of RPE and Certain Rewards on mood were significantly higher
in patients with BPD than in controls. These model parameters correlated significantly
with schema modes, but not with depression severity. Conclusions. BPD is coupled with
altered associations between mood fluctuation and reward processing under uncertainty.
Our findings seem to be BPD-specific, as they stand in contrast with the correlates
of depressive symptoms. Future studies should establish the clinical utility of these
alterations, such as predicting or assessing therapeutic response in BPD.
