The way we are shapes the way we grow old: how personality influences cognitive decline in aging

Given the global increase in life expectancy, research has been focused on identifying factors that may prevent or delay dementia, one of the leading causes of disability in late life and a major public health and economic challenge. Aging trajectories are shaped by multiple individual factors, indicating that dementia represents only one of several possible outcomes of the aging process. Approximately 45% of dementia risk is attributable to modifiable factors, many of which are strongly influenced by personality. Among the determinants of cognitive aging, personality has emerged as a key source of individual differences in health and cognition, affecting emotional regulation, stress management, and engagement in cognitively stimulating activities. The Big Five framework remains the most widely used model to describe enduring patterns of behavior, emotion, and thought. Personality not only shapes the occurrence of risk factors, but also fosters protective mechanisms such as cognitive reserve (CR), which accumulates across the lifespan through mentally and socially enriching experiences. Building on these premises, the present thesis investigates the mechanisms through which personality influences cognitive aging, integrating evidence across distinct yet complementary levels of analysis. It begins with a systematic review of studies examining the role of personality on risk for mild and severe cognitive decline. Consistent with hypotheses, the review confirmed Neuroticism as a robust risk factor for cognitive decline, whereas Openness and Conscientiousness emerged as protective traits. The roles of Extraversion and Agreeableness appeared less consistent, suggesting context-dependent effects. Grounded in these findings, two empirical studies were conducted to clarify the pathways linking personality and cognitive health. The first study explored the relationship between personality and heart rate variability (HRV) – a psychophysiological marker of emotional and cognitive regulation – in adults over 50 years of age. Cognitive reserve was tested as a potential mediator, given its theoretical links to both personality and prefrontal mechanisms underlying HRV. Results showed that personality traits and CR significantly predicted HRV: Openness exerted a positive effect both directly and indirectly through CR, whereas Neuroticism influenced HRV only indirectly via CR. These findings suggest that personality-related differences in autonomic flexibility may reflect underlying variations in cognitive resilience. The second study extended the investigation to the cognitive-behavioral level by assessing cognitive performance across distinct domains through a neuropsychological battery. It examined both the Big Five traits and their higher-order dimensions – Stability and Plasticity – and employed aquadratic approach to test potential non-linear associations. The findings provided partial support for such non-linear effects. Moreover, the study explored the independent mediating roles of cognitive reserve, sleep quality, and modifiable lifestyle-related risk factors in the personality–cognition relationship. Notably, Neuroticism was associated with poorer global cognition through its negative impact on sleep quality, further underscoring the interplay between personality, behavior, and cognitive health. Taken together, the results of this thesis corroborated the multidimensional nature of aging, emphasizing the role of personality in shaping cognitive trajectories. By highlighting the mediating roles of modifiable factors such as cognitive reserve and sleep, this work offers valuable insights for clinical prevention and early intervention strategies. Understanding personality’s role in cognitive aging may thus inform personalized approaches to promote resilience and maintain cognitive health in later life.