Browsing by Author "Huuskonen, Melissa"

Objectives. Numerous prior studies have indicated a relationship between depression and cognitive performance, but the direction of this relationship has yielded partly conflicting results. Clarifying the nature and direction of this relationship is imperative because a clearer understanding may help to target preventive measures more effectively and improve diagnostic accuracy. This prospective, bidirectional sibling study examines how cognitive ability in adolescence is related to depressive symptoms in middle age and how depressive symptoms are related to cognitive performance in late middle age. This study seeks to provide further information about the nature of the relationship between these phenomena in a non-clinical context as well as at the level of individual depressive symptoms instead of diagnosed depression. The heterogeneous symptomatology of depression has been argued to complicate the evaluation of its associations with other phenomena. Methods. The data for this study was collected as part of the Wisconsin Longitudinal Study, in which comprehensive information about the participants was gathered for 56 years. To assess the relationship between adolescent cognitive ability and depressive symptoms in middle age, the results of 2367 sibling pairs (N = 4734) were examined. To evaluate the relationship between depressive symptoms in middle age and cognitive performance in late middle age, the results of 543 sibling pairs (N = 1086) were analysed. The uniqueness of the design and the comprehensiveness of the data allowed for controlling the effects of multiple variables that could potentially explain the relationship between these phenomena. Depressive symptoms in middle age were measured using the Center for Epidemiologic Studies Depression Scale. Similar questions were grouped into four symptom categories, which represented the following individual depressive symptoms: depressed mood, somatic disturbances, relationship problems, and low positive mood. Cognitive performance in adolescence was measured using the Henmon-Nelson Test of Mental Ability intelligence test and in late middle age administering a cognitive test consisting of six tasks. Relationships were first examined using linear mixed models, and the analyses were repeated in sibling analyses using fixed-effects regression. Results and conclusions. Lower cognitive ability in adolescence was found to be associated with higher scores for each individual depressive symptom in middle age. However, no relationship was found between depressive symptoms in middle age and cognitive performance in late middle age for any depressive symptom. Individual symptoms were thus similarly related to the cognitive phenomena studied, but differences were observed in the strengths of these relationships. These varying strengths emphasize the importance of research at the symptom level. Lower cognitive performance seems to predict depressiveness, and this finding could aid in enhancing diagnostic precision and treatments.