Age Related Decline in Memory: Examining the Mediation Effect of Processing, Executive Functioning and Intelligence in Normal Adults

Multiple mediation analyses that collectively examine the prominent theories of cognitive aging (i.e., Common Cause, Processing, and Executive Decline Hypotheses) along with other cognitive domains that are sensitive to aging are rare. Moreover, having identified that cognition begins to decline as early as 30 years old, few studies have examined the mechanisms that underlie memory change among younger aging individuals. As a result, it is unclear whether relevant mediating variables have been excluded from early research on age-related memory decline, or to what extent rehabilitative strategies are applicable as early interventions for maintaining cognitive functioning into late life. The present study was designed to examine a multiple mediation model in which processing speed, verbal working memory, executive functioning, visual working memory, and verbal IQ served as potential explanatory variables in the relationship between age and episodic memory among individuals aged 16 to 70 years. Visual and auditory memory outcome variables were examined separately. Both visual and auditory memory proved to be sensitive to aging, but not equally so. In this investigation, auditory and visual memory did not mature symmetrically, as individuals age. The present results showed that memory decline among aging adults was a sensory-specific, functional by-product of the interactive effects of the mediators in the model. Another notable finding was that verbal IQ was found to be the only variable to have a significant indirect effect on the relationship between age and auditory memory, after controlling for the other mediators in the model. For the relationship between age and visual memory, both verbal IQ and visual working memory were found to have significant indirect effects. Verbal IQ emerged as a salient compensatory mechanism underlying age-related memory decline by acting in opposition to commonly discussed mediators, such as processing speed, working memory, and executive functioning. As a result, neither the Processing nor the Executive Decline hypotheses proved significant. In terms of the mediators that stood out, only the mediated effect of verbal IQ was significantly larger than verbal working memory for the auditory memory outcome. The indirect effect of visual working memory was larger than verbal working memory, as well as all other variables in the model except for processing speed. The present study is clinically relevant as it provided evidence for what cognitive factors, when considered together, are most salient targets for cognitive remediation and neuroprotective interventions. Particularly among the middle-aged and older adult population, age may not be associated with such significant declines in memory if visual working memory and verbal IQ can be maintained