Personality Stability and Change in Alzheimer’s Disease and Major Depressive Disorder

Abstract

Background: Is personality a source of resilience and/or diathesis for behavioral disorders? Alternately, are some personality profiles part of the pathology of these disorders? Answers to these questions inform our understanding of personality and the brain and the etiology of behavioral disorders. Our understanding of these issues is constrained in three ways: (1). much of the research is cross-sectional and thus does not allow for inference about precedence or causality. (2). Many behavioral disorders are not curable, and hence we cannot contrast the post-recovery and premorbid personality with that measured while the disorder was present. (3). Different disorders exhibit different relationships with personality. Aims: This chapter explores personality change and stability by focusing on two disorders: Alzheimer’s disease (AD) which has a chronic and progressive course and major depressive disorder (MDD) which is episodic in nature. Both are contrasted with age-appropriate normal development (ND) in controlled studies. These disorders were chosen because they are serious and debilitating but have contrasting courses. Results: Personality profiles do indeed provide protection or increase risk for both disorders. Resilience to both AD and MDD is conferred by high self-directedness and low harm avoidance or, in other terms, low neuroticism and high conscientiousness; and the inverse profile increases risk for both. There is an association between the change in personality and brain pathology and biomarkers of disease progression, suggesting distinct mechanisms of pathophysiology for AD and MDD. The degree of change seen in the course of AD is greater than that seen in MDD and much greater than that seen in ND over development. For MDD personality change is linked to depressive episodes, and although personality changes more in MDD patients than in the ND controls, the change is reversible for patients who respond to therapy. Conclusions: There does seem to be a causal relationship between personality profiles and AD and MDD and between the progression of the disorders and personality change. The extent and pathophysiology need further research and elaboration.