Dysregulated Emotion Processing in Euthymic Bipolar I: An ERP and Facial EMG Investigation

Background Emotion regulation (ER) disturbances and heightened emotional reactivity are considered trait-like features of bipolar I disorder (BD-I). Neurobiological models link these alterations to disrupted prefrontal-limbic connectivity and impaired top-down control. This study investigated two ER strategies—distraction and reappraisal—in euthymic BD-I and matched healthy controls (HC), examining subjective experience, electrocortical activity (P300, LPP), and facial muscle responses (corrugator, zygomaticus). Methods Participants (nBD-I = 22; nHC = 22) viewed positive, negative, and neutral IAPS images while instructed to passively view, reappraise, or distract via mental calculations. Emotion ratings were collected after each trial. Event-related potentials (ERPs) and facial electromyography (EMG) were recorded. Trait ER was assessed using the Cognitive Emotion Regulation Questionnaire (CERQ). Results During passive viewing, BD-I reported elevated affect to neutral and positive images and showed heightened early corrugator activity, while ERP responses did not differ between groups. During ER, HC showed robust LPP and EMG attenuation across ER strategies and valences. BD-I showed reduced or delayed modulation—particularly during reappraisal of positive affect—despite some self-reported downregulation, which was less pronounced compared to HC. Zygomaticus activity remained elevated in BD-I during positive affect regulation. BD-I also reported greater habitual use of maladaptive strategies (rumination, catastrophizing) and lower use of positive reappraisal. Limitations Small sample size, and no arousal ratings constrain generalizability. Conclusions Findings suggest valence- and modality-specific ER impairments in euthymic BD-I, particularly for positive affect, consistent with partial dissociation across emotion response systems.