Two new studies assess how working memory — the memory we use on a day-to-day basis in decision-making processes — is affected by age, mood, and sleep quality and whether these factors impact memory together or on their own.

Working memory is the short-term memory that a person uses on a daily basis while navigating the world, assessing situations, using language, and making decisions.

As a person advances in age, this faculty tends to decline, but there are also other factors — particularly depressed mood and low sleep quality — that can affect it, both in the short and long terms.

A team of researchers from four institutions — the University of California, Riverside, the University of California, Berkeley, the University of Michigan, in Ann Arbor, and the National Institute of Neurological Disorders and Stroke, in Bethesda, MD — has recently conducted two studies looking at the factors that impact working memory.

Unlike previous research, however, the new study looks at how these factors affect both the qualitative and quantitative aspects of working memory. These terms refer, respectively, to the strength and accuracy of working memory, and how likely it is that memories associated with this faculty are stored in the brain.

The team — whose findings now appear in the Journal of the International Neuropsychological Society — also wanted to understand whether the factors affected working memory independently or whether they influenced each other, then acted on this mental faculty in unison.

"Other researchers have already linked each of these factors separately to overall working memory function, but our work looked at how these factors are associated with memory quality and quantity — the first time this has been done," explains lead researcher Weiwei Zhang, Ph.D.

"All three factors are interrelated," he continues, saying: "For example, seniors are more likely to experience negative mood than younger adults. Poor sleep quality is also often associated with depressed mood."

Impact on quality vs. quantity

After looking at studies that analyzed these factors separately, the researchers wanted to consider them together.

"The piecemeal approach used in previous investigations on these relationships — examining the relationship between one of these health-related factors and working memory — could open up the possibility that an observed effect may be influenced by other factors," notes Zhang.

The current research included two separate studies with findings that were complementary. For the first study, the investigators recruited 110 college students, who they asked to provide self-reported measures regarding their regular sleep quality and their experience with depressed moods.

Then, the research team assessed how these measures related to the participants' working memory performance.

In the second study, the researchers extended their assessment to people of different ages, recruiting 31 participants from the local community, with an age range between 21 and 77 years. The diversity in ages allowed the authors to investigate the connection between age and the functioning of working memory.

The two studies revealed, first, that a person's age is inversely related to qualitative working memory, meaning that, the more we age, the less accurate our working memory becomes.

At the same time, the researchers found that experiencing depressed moods and poor sleep quality is linked to worse quantitative working memory. That is, the less we sleep and the more often we experience negative moods, the less likely it is that we will store short-term memories.

Finally, while the team acknowledges that sleep quality, mood, and age all contribute to working memory decline, their statistical analysis suggests that each factor most likely acts on this faculty independently, and so might be tied to different underlying mechanisms.

"We are more confident now about how each one of these factors impacts working memory," says Zhang, explaining that a better understanding of the elements that impact memory could also have significant clinical implications.

"This could give us a better understanding of the underlying mechanism in age-related dementia. For the mind to work at its best, it is important that senior citizens ensure they have good sleep quality and be in a good mood." -Weiwei Zhang, Ph.D.