Persons with borderline personality disorder (BPD) experience heightened emotional instability. Different components underlie instability, and the relation between instability and well-being could be confounded by average emotionality and within-person standard deviation across emotional states, reflecting variability. Therefore, the goal was to examine which pattern of emotion dynamics parsimoniously captures the emotional trajectories of persons with BPD. Forty persons with BPD, 38 clinical controls in a major depressive episode, and 40 healthy controls rated the intensity of their emotions 10 times a day for 1 week. After correction for differences in average emotionality, persons with BPD showed heightened emotional instability compared to both control groups. When additionally correcting for emotional variability, the authors found that instability indices did not differ between groups anymore. This shows that persons with BPD differ from control groups in the magnitude of emotional deviations from the emotional baseline, and not necessarily in the degree of abruptness of these deviations.

Background Major Depressive Disorder (MDD) is the leading cause of disability worldwide. The cardinal features of MDD are depressed mood and anhedonia. Anhedonia is defined as a “markedly diminished interest or pleasure in all, or almost all, activities of the day”, and has generally been investigated on group-level using retrospective data (e.g. via questionnaire/interview). However, inferences based on group-level findings not necessarily generalize to daily life experiences within individuals. Methods We repeatedly sampled pleasurable experiences within individuals’ daily lives by means of Experience Sampling Methods, and compared how positive affect unfolded in the daily life of healthy controls versus patients diagnosed with MDD and anhedonia. We sampled Positive Affect (PA) and reward experiences on 10 semi-random time points a day, for seven days in the daily lives of 47 MDD patients with anhedonia, and 40 controls. Results Multilevel models showed that anhedonia was associated with low PA, but not to differences in PA dynamics, nor reward frequency in daily life. In reaction to rewards, MDD patients with anhedonia showed no difference in their increase in PA (i.e., PA reactivity), and showed no signs of a faster return to baseline thereafter (i.e., PA recovery). Conclusions Our results suggest that the dynamical signature of anhedonia in MDD can be described best as a lower average level of PA, and “normal” in terms of PA dynamics, daily reward reactivity and reward recovery. Preregistration: https://osf.io/gmfsc/register/565fb3678c5e4a66b5582f67 . Preprint: https://osf.io/cfkts