Effects of diminished positive mood and depressed mood upon verbal learning and memory among people with multiple sclerosis

Objective: Cognitive impairment affects as many as 65% of people with multiple sclerosis (PWMS), and memory impairment confers greater severity of disability and functional impairment. Depression is also common among PWMS, and lifetime prevalence rates are as high as 50%. Research has yet to clearly define the relationship between memory dysfunction and depression among PWMS, and may reflect incomplete assessment of depressive symptoms. The present study examined different aspects of depressive symptoms including anhedonia (i.e., diminished positive mood) and their relationships with verbal learning and memory among PWMS. Method: Participants were 48 healthy individuals and 96 PWMS. They were primarily Caucasian (90.3%) and female (75.0%). Participants completed the California Verbal Learning Test-2 (CVLT-2) to assess verbal learning and memory and the Chicago Multiscale Depression inventory to assess depressed mood (CMDI-Mood) and diminished positive mood (CMDI-DPM). Results: Linear regression revealed that the main effect of CMDI-DPM and the interaction of CMDI-DPM and CMDI-Mood significantly explained variance across learning, recall, and recognition CVLT-2 indices. Follow-up analyses indicated that CMDI-DPM was only significant in the absence of high CMDI-Mood scores. CMDI-Mood explained variance in only CVLT-2 Trial B. Conclusions: Depressed mood had little direct effect upon memory performance in PWMS. In the absence of severe depressed mood, higher levels of positive mood corresponded to better memory performance. However, the impact of diminished positive mood was rendered null among those endorsing high levels of depressed mood. These data may imply that anhedonia corresponds with poorer memory function among PWMS, and suggests that investigators and clinicians should assess multiple mood dimensions among PWMS.