It is widely reported that persons with major depressive disorder (MDD) show impaired performance on cognitive functioning, including frontotemporally mediated cognitive functions. The presence of cognitive dysfunction among patients with dissociative symptoms in trauma-related disorders may contribute to poorer treatment outcomes. Patients with major depressive disorder (MDD) frequently report dissociative symptoms. Here we investigate association of dissociative symptoms and neurocognitive dysfunction in patients with depression. We predicted that higher levels of dissociative symptoms among persons with MDD would be associated with lower scores on objective measures of frontotemporally mediated neurocognitive functions.

Patients who met DSM-V diagnostic criteria for a primary diagnosis of recurrent MDD were recruited. The Hamilton Rating Scale for Depression (HAM-D) was administered to assess the severity of depressive symptoms. To assess dissociative symptoms participants completed the Multiscale Dissociation Inventory (MDI). Two groups of patients were selected and matched. One group consisted of 13 patients having MDD and dissociative symptoms and second group consisted of 12 patients having MDD only. To measure frontotemporally mediated cognitive functioning following tests were administered: Color Trails Test; Wisconsin Card Sorting Test; Conners’ Continuous Performance Test (CPT). To examine group differences on clinical and neuropsychological scores, two-tailed independent samples t-tests was performed.

Group comparisons of performance on neuropsychological tests showed that participants with depression and dissociative symptoms performed worse on Color Trails Test Part 2 completion time, a measure of mental flexibility and processing speed. MDI depersonalization scores were correlated with measures of processing speed, mental flexibility and sustained attention. Specifically, Color Trails Test Part 2 scores were negatively correlated with depersonalization symptoms, where lower scores indicate slower completion time. Depersonalization symptoms on the MDI were also related to the CPT Hit Reaction Time Interstimulus Interval Change (a measure of vigilance), such that higher levels of depersonalization were related to better performance in a less active environment.

Our results suggest that dissociation is related to specific subtle impairments in neurocognitive functioning. Dissociative symptoms should ideally be assessed before treatment, as they may influence MDD treatment response. The findings point towards the need to further examine the impact of dissociation on functioning in patients with depression.

The authors have not supplied their declaration of competing interest.