Misperceiving momentum: computational mechanisms of biased striatal reward prediction errors in bipolar disorder

Abstract

BackgroundDysregulated reward processing and mood instability are core features of bipolar disorder that have largely been considered separately, and with contradictory findings. We sought to test a mechanistic account that proposes that, in bipolar disorder, there is an excessive tendency to enter recursive cycles in which reward perception is biased by signals that the environment might be changing for the better or worse. MethodsParticipants completed a probabilistic reward task with functional Magnetic Resonance Imaging. Using an influential computational model, we ascertained whether participants with bipolar disorder (n = 21) show greater striatal tracking of momentum-biased reward prediction errors (RPEs) than healthy controls (n = 21). We conducted psychophysiological interaction analyses to quantify the degree to which each group modulated functional connectivity between the ventral striatum and left anterior insula in response to fluctuations in momentum. ResultsIn the bipolar disorder group, but not controls, the momentum-biased RPE model accounted for significant additional variance in ventral striatal activity beyond a standard mode of veridical RPEs. Compared to controls, the bipolar disorder group exhibited lower ventral striatal-left insular functional connectivity modulated by momentum-biased RPE. Moreover, this reduction in connectivity was more pronounced as a function of current manic symptoms. ConclusionsConsistent with an existing theory, we found evidence that bipolar disorder is associated with a tendency for momentum to excessively bias striatal tracking of RPE signals. We identify impaired striatal-insular connectivity as a possible locus for this propensity. We argue that computational psychiatric approaches that examine momentary shifts in reward and mood dynamics have strong potential for new mechanistic insights and targets for intervention.