Personality functioning as a dimensional context for mentalization and neurocognition in borderline personality disorder

Personality functioning (PF), neurocognition, and mentalization are all implicated in borderline personality disorder (BPD), yet their joint pattern and their dimensional associations with PF remain insufficiently characterized. This study compared individuals with BPD and healthy controls (HCs) across these domains and examined their associations with PF severity. Sixty-five psychiatric inpatients with BPD and 58 HCs completed the Level of Personality Functioning Scale-Self Report, the Mentalization Questionnaire, the Imposing Memory Task, and a neurocognitive battery assessing interference control, cognitive flexibility, verbal memory, and event sequencing. Categorical group differences were examined using covariate-adjusted generalized linear and mixed-effects models. Dimensional associations with PF were tested using hierarchical linear regression models. The BPD group showed marked impairment in PF, with particularly pronounced dysfunction in Self-Functioning. They also reported substantially greater self-mentalizing difficulties, whereas performance-based theory-of-mind reasoning showed no significant group difference. Across neurocognitive domains, the BPD group showed poorer interference control, cognitive flexibility, verbal memory, and event sequencing. Task-level analyses indicated poorer latency-based interference control, more frequent set loss, lower immediate verbal episodic memory, and poorer event sequencing. After adjustment for PF severity, cognitive flexibility was the only neurocognitive domain that remained significantly associated with diagnostic group, although this residual group difference was no longer significant after adjustment for psychotropic medication burden. At the dimensional level, greater PF impairment was strongly associated with higher self-reported mentalizing difficulties, poorer interference control and verbal memory after demographic adjustment. After adjustment for diagnostic group, the verbal-memory association remained significant, whereas the interference-control association was attenuated to non-significance. These findings suggest that BPD is characterized by marked impairment in PF, particularly in self-functioning, and that its dimensional severity is most closely related to self-reported difficulties in self-mentalizing and to reduced performance in selected neurocognitive domains, particularly verbal memory and interference control. By contrast, poorer cognitive flexibility may partly reflect psychotropic medication burden, whereas poorer event sequencing may reflect variance shared between diagnostic status and PF severity. Together, the findings support a differentiated account in which PF severity and categorical BPD status show overlapping yet non-identical mentalizing and neurocognitive correlates.