Personality as mechanism: An integrative model of Five Factor Model personality traits as a mechanism between earlier life factors and cognitive aging

Abstract

Models of personality and health emphasize the role of Five-Factor Model personality traits (particularly neuroticism and conscientiousness) in cognitive health outcomes. A complementary literature on lifecourse models of cognitive aging indicate that earlier life factors (socioeconomic status, adverse childhood experiences, childhood health) are critical for later life cognitive function and dementia risk. There is growing evidence that these earlier life factors also contribute to adult personality. The present review integrates models of personality and health into lifecourse models of cognitive aging and posits personality traits as central mechanisms between earlier life factors and cognitive health. Development of a more detailed lifespan model will help identify chains of risk and resilience to promote better late-life cognition, health, and well-being.

Personality traits are associated consistently with cognitive health [1, 2]. As operationalized by the Five Factor Model (FFM), dispositional traits can be summarized across five dimensions: neuroticism (the tendency to feel negative emotions and vulnerability to stress), extraversion (the tendency to feel positive emotions and be sociable), openness (the tendency to be creative and unconventional), agreeableness (the tendency to be trusting and kind), and conscientiousness (the tendency to be organized and responsible) [3]. Of these five traits, neuroticism and conscientiousness are most consistently associated with better cognitive function in older adulthood: Individuals higher in neuroticism and lower in conscientiousness maintain their memory function longer over time [1] and have lower risk of developing Alzheimer’s disease and related dementias [4].

Models of personality and health emphasize the role that personality traits play in health outcomes across the lifespan [5]. In the context of cognitive aging, much of the work on these models has been devoted to identifying the mechanisms through which personality contributes to better cognitive outcomes [6]. Lifecourse approaches to cognitive health recognize the importance of early life factors and the cumulative effect of risk and protective factors that occur earlier in the lifespan on later life cognitive outcomes [7]. Recent evidence suggests that early life factors may contribute to personality in adulthood [8-10], raising the intriguing possibility that personality traits themselves may be a pathway through which early life factors contribute to cognitive health across the lifespan. This review presents a theoretical model that integrates models of personality and health into lifecourse models of cognitive aging. This novel model posits that personality traits are one mechanism through which early life factors contribute to cognitive outcomes across adulthood (Figure 1). We describe each component of this model below.

Figure 1.

Model of Five Factor Model personality traits as a mechanism between earlier life factors and later life cognitive health

Earlier Life Factors → Later Life Cognition (c path)

Lifecourse models of cognitive aging specify that cognitive health in older adulthood is in part the culmination of risk and protective factors across the lifespan [11, 12]. Socioeconomic status (SES) is a prominent factor within these models [13]. Educational attainment is perhaps the strongest and most consistent modifiable predictor of late-life cognitive outcomes: Individuals with more years of education have better cognitive function [14] and lower risk of dementia in older adulthood [15]. In addition to their own level of education, the education of the individual’s parents is also associated with better late-life cognitive health [16]. That is, parental education, as well as the broader socioeconomic environment in which one grows up, has long-lasting consequences for cognitive health in older adulthood [17]. Other factors that are markers of SES are also associated with dementia risk in older adulthood. Household crowding, a measure derived from the Census that is a marker of childhood SES, for example, is associated with greater risk of dementia, in part through the individual’s own educational attainment in adulthood [18]. Such outcomes may be due to the cumulative disadvantage that can be difficult to overcome [19], although higher SES in adulthood may help compensate for earlier life disadvantages [20].

In addition to the broad socioeconomic environment of childhood, more specific experiences, including adverse childhood experiences and childhood health, are also associated with late-life cognition. Individuals who experienced physical neglect or emotional abuse as children, for example, have a greater risk of dementia in older adulthood, as do those who have a greater number of adverse experiences [21]. Such experiences are likewise associated with worse cognitive function in general [22], and worse processing speed and verbal fluency in particular [23] prior to dementia in older adulthood. In addition, individuals who had poor health as children tend to have worse cognitive function and greater risk of dementia [17]. Such findings highlight that the circumstances and experiences that occur during development can have lasting consequences for cognitive aging.

Personality → Later Life Cognition and Dementia Risk (b path)

As described above, personality traits are associated consistently with cognitive health across the lifespan, including older adulthood. Of the Five-Factor Model traits, the association with cognitive function and dementia risk tends to be the most consistent for neuroticism and conscientiousness. Individuals higher in neuroticism, for example, report more cognitive symptoms [24], perform worse on cognitive tasks across a variety of domains, from processing speed to visuospatial ability [25], make more cognitive errors [26], are more likely to have subjective cognitive decline [27], are at greater risk of developing dementia [28], and are less likely to transition back to healthy from impaired status [29]. Individuals higher in conscientiousness, in contrast, have better outcomes across many of these aspects of cognitive health [24-29]. Finally, even after the onset of cognitive impairment, personality continues to be predictive of dementia-related outcomes. Individuals higher in neuroticism and lower in conscientiousness, for example, are more likely to experience behavioral and psychological symptoms of dementia, such as emotional dysregulation or decreased motivation, as reported by a caregiver [30].

Lifespan models of personality and health theorize that behavioral and clinical patterns associated with these traits are mechanisms that explain the association with health outcomes [31], including cognition [32]. Individuals higher in neuroticism and lower in conscientiousness, for example, are less physically active [33] and more likely to smoke and use other substances [34], which increases risk of dementia [35]. These traits are likewise associated with clinical risk factors, such as mid-life obesity [36], depression [37] and late-life hearing impairment [38], which are associated with greater dementia risk [35]. Neuroticism and conscientiousness further shape social factors, such as loneliness [39], that contribute to worse global cognitive function [40] and dementia risk [41].

Earlier Life Factors → Personality (a path)

As reviewed above, a large share of the research on personality and health has focused on personality as risk factors for health-related behaviors and outcomes. Less research has been devoted to the early life factors that contribute to adult personality. Traditional models of personality development have long emphasized the biological basis of personality traits, particularly genetics [42]. Behavioral genetics models use data from twins to model variance explained by genetic, shared environmental, and nonshared environmental factors [43]. These models tend to find that personality traits are moderately heritable (about 50% based on twin studies and 20% based on family and adoption studies) with the remaining variance generally due to nonshared environmental factors [43]. Large meta-analyses examining the molecular genetics of personality traits have found that personality variation is not due to one or two single nucleotide polymorphisms but rather the combined effect of a vast number of common genetic variants [44]. Molecular genetics studies further indicate that the heritability of personality tends to be lower (<10%) [44], although genome-wide studies estimate narrow heritability based mainly on additive effects while twin studies estimate broad heritability that also includes rare variants and non-additive effects.

This shift in understanding of the origins of personality traits has led to renewed interest in identifying environmental factors that contribute to personality traits across the lifespan. And, indeed, there is growing evidence that personality traits are shaped, in part, by early life environmental factors. One basic early life factor is the socioeconomic environment in which the person grows up, which, as described above, is critical for late-life cognitive health [14, 16]. One aspect of childhood SES is parental education, which is associated with offspring personality in adulthood. Parents with more education (either mothers or fathers) have offspring who score higher in openness and extraversion and lower in neuroticism [8]. These associations are apparent even among offspring who were adopted, which indicates the association between parent education and offspring personality is transmitted (at least in part) environmentally rather than solely genetically [8]. The association between childhood SES and personality starts early and is not limited to parent education. Children who live in neighborhoods with lower SES tend to score higher in aspects of neuroticism and lower in aspects of conscientiousness, associations that are independent of and in addition to the association between family SES and these characteristics [45].

Also similar to cognitive health, aspects of childhood beyond SES have been associated with adult personality traits. Adverse childhood experiences that have been implicated consistently in poor health outcomes in adulthood [46] also shape adult personality [47]. Individuals who experience any type of adverse experience (e.g., abuse, neglect) in childhood are higher in neuroticism and lower in conscientiousness as adults [9]. Childhood health has likewise been associated with adult personality. Individuals who report being in poor health as children tend to score higher in neuroticism and lower in conscientiousness in adulthood [10]. And individuals who were breastfed as infants (as reported by their mothers) are lower in neuroticism and higher in openness in adulthood [48]. Thus, many of the earlier life environmental factors that predict cognitive outcomes in later life are also predictive of adult personality.

There are several reasons why limited economic resources and adverse experiences in childhood may shape the development of personality traits that individuals carry into adulthood. The chronic stress associated with both lower SES and adversity may have behavioral (e.g., heighted vigilance, avoidance) and physiological (e.g., inflammation) consequences that contribute to trait development, particularly neuroticism and conscientiousness. Individuals may also develop strategies that maximize safety. Such strategies are likely to be adaptive in the short term but may undermine trait development and potentially health outcomes in the long term. Fewer economic resources and experiences with adversity may reduce the ability to effectively regulate emotions and behavior that consolidate into higher neuroticism and lower conscientiousness in adulthood.

Personality as a Mechanism of Lifespan Cognitive Health (ab/c’ paths)

The evidence from the broader literature on earlier life factors, personality, and cognition in older adulthood supports the theoretical model that implicates personality traits as a mechanism of the association between early life background and experiences and later life cognitive health. As reviewed above, empirical evidence supports each of the paths of this model and there is emerging evidence from studies that consider all paths simultaneously. Sesker and colleagues [49], for example, found that the association between the early life socioeconomic environment and later life risk of cognitive impairment was mediated by adult personality traits. Specifically, individuals who grew up with few economic resources tended to score higher in neuroticism and lower in conscientiousness in adulthood than individuals who grew up with more resources, and these two traits mediated the association between early life SES and risk of dementia in older adulthood; this pathway was not apparent for the other three traits (extraversion, openness, agreeableness). Conde-Sala and Garre-Olmo [50] found that experiencing the death of a parent in childhood was associated with both higher neuroticism and higher risk of dementia in older adulthood, and that higher neuroticism may contribute, in part, to the greater dementia risk associated with this early loss. The mediation also extends to cognitive function, in addition to impairment risk: Individuals who experienced adversity in childhood score higher in neuroticism in adulthood, which mediates the association between childhood adversity and executive function in adulthood [51]. Neuroticism was the only one of the five traits tested in these latter two studies. This growing literature thus provides support for a more comprehensive model of personality and cognitive health that outlines how early life experiences shape adult personality functioning as one mechanism to later life cognitive health.

Conclusion

The integration of models of personality and health into lifecourse models of cognitive aging provides a more comprehensive model to better identify chains of risk and resilience for cognitive health across the lifespan. Such a model connects life circumstances and personality factors and their mutual influence over time. For instance, poverty (risk) could lead to higher neuroticism (risk), increasing susceptibility to chronic diseases (risk), but higher SES or conscientiousness in adulthood (resilience) could buffer these effects. Such research is difficult, especially because ideally the paths would be tested simultaneously, which requires longitudinal lifespan data that ranges from early life to older adulthood. Many of these pathways are also likely to be reciprocal, which should also be tested. Still, by mapping these chains, we can pinpoint crucial stages where interventions may be most effective. Addressing an early risk factor can hopefully disrupt the chain, preventing poor health outcomes later in life. In contrast, bolstering resilience factors (e.g., increasing conscientiousness, reducing neuroticism) at any point could mitigate the impact of accumulated risks. This integrative conceptual model can be used to foster and guide future research to better understand the mechanisms through which earlier life factors lead to Alzheimer’s disease and related dementias. By accounting for the life history and complex realities that individuals and communities face, such research may identify points of prevention and intervention that are more likely to promote and achieve healthier cognitive aging.