Description
Alzheimer's Disease (AD) is a progressive and fatal brain disorder that is characterized by memory loss, behavioral change, and cognitive impairments resulting from neuronal degeneration. Declines in olfactory function occur early in the course of the disease and are evident before other cognitive impairments. Advancing age and possession of the _4 isoform of the apolipoprotein E Gene (apoE) are risk factors for both AD and olfactory function impairment, yet it is likely that both environmental and genetic factors contribute to AD pathology. Stress is an environmental factor that impacts the aging process through physiological and psychological processes. Glucocorticoids (GCs) are hormones that are released during stress, and have been implicated as potentially important in the development of AD. Recent studies demonstrated an interactive impact of stress and apoE _4 on cognitive impairment, but to date, no one has reported on the potential impact of stress and apoE _4 on olfactory function. Elucidating the mechanisms of action that lead to impaired olfaction for those at risk for AD may help inform techniques for prevention and early detection of the disease. The current study examined the effect of stress and the apoE _4 allele on olfactory learning and memory in 32 young and 32 older adults. Stress was operationally defined using the Penn State Worry Questionnaire (PSWQ; subjective stress) and Cortisol Awakening Response (CAR; physiological stress). It was hypothesized that there would be (1) a main effect of stress on odor memory and learning, (2) an apoE by stress interaction such that individuals with at least one apoE _4 allele would have a greater decline in olfactory scores as stress scores increased than individuals with no apoE _4 allele, and (3) an age effect such that the stress and apoE interaction would be evident in older but not younger adults. Subjective stress improved performance on immediate recall across trials, short and long delay free recall, and odor identification. When participants were given cues after a delay, _4- older and younger adults improved odor recall as PSWQ scores increased, while _4+ younger adults did not improve, and older _4+ adults recalled less as PSWQ scores increased. Use of serial clustering was affected by CAR in those individuals who were CAR responders such that increasing CAR appeared to be associated with increasing use of serial clustering for _4- individuals, and with decreasing use for _4+ adults. Recognition scores were not significantly affected by either stress measure. Taken together, these findings suggest that stress may affect olfactory memory differentially depending on apoE _4 status. Some support was found to suggest that CAR may be associated with use of certain learning techniques for CAR responders, and further studies are needed to confirm these findings in larger samples.
