Depression and borderline personality disorder (BPD) are frequently comorbid psychiatric disorders that reliably share deficits in executive functioning (EF). In addition to EF, meta-analytic evidence indicates that processing speed and verbal memory are also affected in depression and BPD, but the impact of BPD further spans the domains of attention, nonverbal memory, and visuospatial abilities. Suicidality is a notable phenotypic commonality in depression and BPD. Neuropsychologically, there are consistent discrepancies between individuals who have and have not thought about suicide in global cognitive functioning, as well as between those who have attempted suicide and those who have just thought about suicide in EF. This study aims to replicate the effect size differences between these groups and explore whether neuropsychological functioning relates to dimensional measures of psychopathology.

Right-handed women between the ages of 18 and 55 were recruited into one of three diagnostic groups: a) current major depressive episode (MDD; n=22); b) current major depressive episode with comorbid BPD (MDD+BPD; n=19); and c) absence of current major depressive episode and BPD (controls; n=20). Groups were also classified based on historical suicide attempt and on the presence or absence of historical suicidal ideation. Exclusions included bipolar disorder, neurodevelopmental disorder, moderate/severe brain injury, neurological illness, serious physical illness, eating disorder, and moderate/severe alcohol/substance use disorder. Participants were administered the Zanarini Rating Scale for Borderline Personality Disorder (ZAN-BPD), Beck Depression Inventory (BDI-II), Interpersonal Needs Questionnaire (INQ), UPPS-P Impulsive Behavior Scale, Everyday Memory Questionnaire, Brief Visuospatial Memory Test (BVMT), California Verbal Learning Test (CVLT), Delis-Kaplan Executive Function System (D-KEFS) Color-Word Interference Test, D-KEFS Trail Making Test, D-KEFS Verbal Fluency, Wechsler Adult Intelligence Scale-IV Coding and Digit Span subtests, Wechsler Memory Scale-IV Logical Memory, and Wechsler Test of Adult Reading.

With one exception, analyses of raw scores indicated there were no significant neuropsychological differences between groups based on diagnosis, historical suicidal ideation, and suicide attempt (p>.05). However, individuals with MDD+BPD, historical suicidal ideation, or suicide attempt endorsed more memory complaints than the other groups with large effect size differences. Differences in self-reported impulsivity indicated large effects between controls and MDD+BPD, moderate to large effects when comparing controls to MDD and MDD to MDD+BPD, and moderate effects among the suicidal ideation and suicide attempt groups. Impulsivity was rated highest in those with MDD+BPD, historical suicidal ideation, or suicide attempt. These analyses applied false-discovery rate correction and adjusted for age. Using ridge regressions to separately predict depressive symptoms, BPD symptoms, and suicide risk factors, neuropsychological indices were most associated with suicide risk factors and explained 22.8% of INQ variance. Conversely, these indices explained 9.6% of ZAN-BPD variance and 0.6% of BDI-II variance.

The neuropsychological literature on BPD describes moderate crosscutting neuropsychological dysfunction, and clarifying the distinct cognitive alterations associated with comorbid psychiatric disorders and suicide phenomena offers novel avenues of research for investigating their mechanisms. While neuropsychological functioning may not strongly relate to psychiatric symptomatology, it may contribute to meaningful algorithms of suicide risk in individuals with depression and BPD.