Factors that positively or negatively mediate the effects of age on working memory across the adult life span.

Working memory abilities significantly decrease with advancing age; hence, the search for factors that may increase or mitigate this decline is critical. Several factors have been identified that influence working memory; however, their effects have been mainly assessed separately and rarely together with other factors in the same sample. We examined 120 variables to search for factors that jointly act as mediators of working memory decay across the adult life span. A sample of 1652 healthy adults was assessed in spatial and verbal working memory domains. Structural equation modeling analyses were conducted to search for potential mediators that intervened between age and working memory. Only 14 and 10 variables reliably mediated spatial and verbal working memory, respectively. Factors from several domains remained in the models, such as individual characteristics, physiological traits, consumption habits, and regular activities. These factors are sufficiently powerful to influence working memory decline when they jointly interact, as in everyday living.

Mediators of episodic memory decay across the adult life span.

The ability to remember the details of our own experiences declines gradually as we get old. The reason for this decay has been attributed to several factors besides age, such as education, nutrient intake and health status. However, the influence of these factors has mainly been examined individually and rarely together. Here we identify those factors that jointly act as mediators of episodic memory decay across the adult life span. We examined source memory in a lifespan sample of 1557 healthy adults. A total of 70 physical, biological and lifestyle variables were measured and introduced into a structural equation model as potential mediators that intervene between age and source memory. Only 14 mediator variables reliably mediated source memory decay; notably, eight of these variables have an effect on the cardiovascular system. The model unequivocally highlights that the mediators that may impair cardiovascular functioning also impact brain resources involved in episodic memory. We identified the factors that are relevant to episodic memory decline when they interact together as occurs in real life.

The decline of verbal and visuospatial working memory across the adult life span.

It has been well established that working memory abilities decrease with advancing age; however, the specific time point in the adult life span at which this deficit begins and the rate at which it advances are still controversial. There is no agreement on whether working memory declines equally for visuospatial and verbal information, and the literature disagrees on how task difficulty may influence this decay. We addressed these questions in a lifespan sample of 1,500 participants between 21 and 80 years old. The n-back task was used, with letters and circles presented at different positions around an imaginary circle, to evaluate working memory in the verbal and visuospatial domains, respectively. The participants' task was to judge whether the current stimulus matched a stimulus that was shown n trials prior. Both domains were evaluated in two levels of difficulty: 1-back and 2-back. The comparison across decades showed that discrimination in the visuospatial and 1-back tasks started to decline earlier in women than in men; however, discrimination was equal between the sexes in the verbal and 2-back tasks. Performance on tasks in the visuospatial domain exhibited more pronounced decline than in those in the verbal domain. The rate of decline in working memory accuracy was superior in 2-back tasks than in 1-back tasks, independent of the domain. These results revealed that the effects of aging on working memory are less dependent on the type of information and more reliant on the resources demanded by the task.

The rate of source memory decline across the adult life span.

Previous studies have suggested that the ability to remember contextual information related to specific episodic experiences declines with advancing age; however, the exact moment in the adult life span when this deficit begins is still controversial. Source memory for spatial information was tested in a life span sample of 1,500 adults between the ages of 21 and 80. Initially, images of common objects were randomly presented on one quadrant of a screen while the participants judged whether they were natural or artificial. During the retrieval phase, these same images were mixed with new ones, and all images were displayed in the center of the screen. The participants were asked to judge whether each image was new or old, and whether it was old, to indicate in which quadrant of the screen it had originally been presented. Source accuracy decreased linearly with advancing age at a rate of 0.6% per year across all decades even after controlling for educational level; this decline was unaffected by sex. These results reveal that either spatial information becomes less efficiently bound to episodic representations over time or that the ability to retrieve this information decreases gradually throughout the adult life span.

Neural correlates of source memory retrieval in young, middle-aged and elderly adults.

Event-related potentials (ERPs) were recorded in young (21-27 years old), middle-aged (50-57 years old) and older adults (70-77 years old) to determine whether the decline in source memory that occurs with advancing age coincides with contemporaneous neurophysiological changes. Source memory for the spatial location (quadrant on the screen) of images presented during encoding was examined. The images were shown in the center of the screen during the retrieval task. Retrieval success for source information was characterized by different scalp topographies at frontal electrode sites in young adults relative to middle-aged and older adults. The right frontal effect during unsuccessful retrieval attempts showed amplitude and latency differences across age groups and was related to the ability to discriminate between old and new images only in young adults. These results suggest that the neural correlates of the retrieval success and attempt were affected by age and these effects were present by middle-age.

Age-related changes in neural activity during source memory encoding in young, middle-aged and elderly adults.

Source memory, the ability to remember contextual information present at the moment an event occurs, declines gradually during normal aging. The present study addressed whether source memory decline is related to changes in neural activity during encoding across age. Event-related potentials (ERPs) were recorded in three groups of 14 subjects each: young (21-26 years), middle-aged (50-55 years) and older adults (70-77 years). ERPs were recorded while the subjects performed a natural/artificial judgment on images of common objects that were presented randomly in one of the quadrants of the screen (encoding phase). At retrieval, old images mixed with new ones were presented at the center of the screen and the subjects judged whether each image was new or old and, if old, were asked to indicate at which position of the screen the image was presented in the encoding session. The neurophysiological activity recorded during encoding was segregated for the study items according to whether their context was correctly retrieved or not, so as to search for subsequent memory effects (SME). These effects, which consisted of larger amplitude for items subsequently attracting a correct source judgment than an incorrect one, were observed in the three groups, but their onset was delayed across the age groups. The amplitude of the SME was similar across age groups at the frontal and central electrode sites, but was manifested more at the posterior sites in middle-aged and older adults, suggesting that source memory decline may be related to less efficient encoding mechanisms.