REINFORCEMENT LEARNING IMPAIRMENT IN PATIENTS WITH EARLY-STAGE PSYCHOTIC BIPOLAR DISORDER

Abstract

Background: Abnormal reward sensitivity is a biosignature to mood disorders spectrum. Recent data suggested either elevated or preserved positive but impaired negative reinforcement learning in patients with bipolar disorder. Functional MRI studies provided extra evidence on heightened reward sensitivity in manic patients. Of note, these investigations mostly rest on chronically ill samples, conditions of whom may have been confounded by prolonged exposure to medications. This study aims to examine reinforcement learning performance and its relationship with symptomology in patients with early-stage psychotic bipolar disorder (BDP). Methods This study is based on 38 patients with early-stage BDP (defined by having received psychiatric treatment for first-episode BDP within 3 years since service entry) who have been euthymic for at least eight weeks and 40 demographically-matched controls. Reinforcement learning performance was evaluated using Gain-vs-Loss-Avoidance Task (GLAT), which measured the correct responses in both gain and loss-avoidance pairs with reinforcement probability at either 90% or 80% across four blocks in the training phase and one block in the test/transfer phase. Comparison analyses on reinforcement learning performance were conducted on two groups. Associations of reinforcement learning measures with symptom scores, cognitive functions and functioning measures were also tested. Results: There was no group difference in gender, age or education level. Repeated-measures analysis of variance (ANOVA) showed significant main effects of group (F=6.52, p=0.013), block (F=43.71, p<0.001), probability (F= 5.58, p<0.001), and block x group (F=2.87, p=0.040) interaction. Post-hoc tests revealed that controls performed better than patients across blocks (p<0.05). Patients also showed a lower lose-shift rate (t= 2.21, p=0.03) and punishment-driven learning accuracy rates (t=2.42, p=0.018) than controls. Marginally significant main effect of stimulus pair (F=3.98, p=0.05) was revealed in the test phase, with controls showing a significantly higher preference in Frequent Winner vs Frequent Loser (FWFL) pair than patients (t=-2.25, p=0.028). No significant correlations between learning measures and any of the symptom dimensions in patient sample. Discussion: Our preliminary findings provided a brief evidence on the negative reinforcement learning impairment in early-stage BDP patients. Further investigation is required to verify and confirm our results of impaired negative reinforcement learning in the initial course of bipolar disorder.