By Nikhil Ramburn and Sat Bir Singh Khalsa, Ph.D.
Working memory is a component of our cognitive system that is responsible for holding and processing information over brief intervals. Researchers believe that working memory is central to cognitive functioning as it correlates with a number of outcomes such as intelligence and scholastic attainment and is linked to basic sensory processes. The expansion and decay of working memory over a lifetime is related to the normal development and degradation of the prefrontal cortex (PFC) in the brain, an area responsible for higher executive functioning.
Our behavioral state and circumstances, at any point in time including factors such as stress level, mood state, and physical activity, appear to play key roles in determining the quality and strength of working memory. For example, acute and chronic physiological stress impair working memory through decreases in PFC neuronal activity. In fact, chronic stress leads to even more profound deficits in working memory and eventual structural changes in the PFC such as an atrophy of neural pathways. In addition, mood states and the production of the neurotransmitter dopamine can impact the efficiency of working memory problem-solving capacity.
Working memory does deteriorate with age and disease. In fact, working memory is among the cognitive functions most sensitive to decline in old age since the PFC deteriorates more than other brain regions as we grow old. Not surprisingly, severe mental illnesses, such as schizophrenia and depression, can also decrease functioning of the PFC and thereby the efficacy of working memory. In childhood learning, working memory deficits correlate to attention, reading, and language challenges. Fortunately, behavioral interventions such as a wide range of physical activities such as yoga, tai chi, qi gong, cycling, running, resistance training, etc., as well as meditation, appear to confer an improvement/enhancement in working memory. One of the few meta-analytic reviews to investigate working memory exclusively found statistically significant evidence that chronic physical activity could improve working memory in healthy subjects whereas short-term physical activity did not confer significant gains.
Mindfulness meditation practices also appear to enhance working memory despite their focus on bringing the wandering mind back to the present moment instead of constantly updating it with new stimuli. In addition, meditation protects working memory against the deleterious effects of stress as reported in a 2010 study of military personnel by the laboratory of Dr. Amishi Jha at the University of Miami, Florida. A 2016 systematic review by researchers from Monash University in Melbourne, Australia, summarized and confirmed these findings. This review focused on outcomes following 8-week training programs such as Mindfulness Based Stress Reduction (MBSR) and examined whether working memory and other executive functions improved as a result of these interventions. Researchers found preliminary evidence for working memory capacity improvement, which could be attributed to the fact that monitoring present moment experience is a key skill of mindfulness practice.
Yoga may prove to be another effective complementary approach for improving working memory since it combines the benefits of exercise, meditation and pranayama (breathing exercises). Yoga has also been shown to improve attention, reduce stress and mood interference and can therefore protect against working memory deficits. Several studies from the prestigious laboratory of Dr. Edward McAuley at the University of Illinois focused on the relationship between yoga and cognition. In a 2014 study, 30 female college-aged participants completed both a yoga exercise session and an aerobic treadmill exercise session on separate days. The results showed significantly higher scores on working memory tasks after the yoga exercise as compared to the aerobic and baseline conditions. More recently, in 2016, the McAuley lab researchers looked at the effects of an 8-week yoga intervention on sedentary older adults (averaging 62 years old). The participants were randomized to a thrice weekly hatha yoga class which included yoga poses, meditation, breathing, and mantra or a stretching control group. The findings showed improved working memory performance in the yoga group, which appeared to be mediated by decreased stress as determined by outcome measures such as salivary cortisol levels. This encouraging evidence points towards yoga’s potential to decrease cognitive decline in older adults by protecting their PFC from the effects of stress.
A landmark study in 2017 by researchers at the Department of Psychology, Texas State University aimed to assess the impact of yoga on specific working memory subconstructs such as ‘maintenance’ and ‘manipulation’ tasks. Working memory subtests can differentiate and evaluate between short-term storage (maintenance) and manipulation of task-relevant information from both short-term and long-term storage (manipulation). Forty-three healthy subjects (8 males, 35 females) participated in 6-sessions of 60-minute yoga classes. The hatha yoga program consisted of asana (yoga exercises) connected with pranayama (breath exercises) and concluded with mindfulness meditation in supine rest. This yoga intervention was associated with improvement on both ‘manipulation’ and ‘maintenance’ working memory measures as well as enhanced mindfulness scores. This study ads valuable insight into the potential of yoga training for cognitive enhancement.
Another notable study investigated the effects of combining yoga and working memory training among healthy middle aged adults. Researchers from Manipal University in Mangalore, India, randomly assigned a total of 45 participants into 3 groups. Group 1 received both yoga and working memory training whereas group 2 received only working memory training, and group 3 was the no-training control. Both working memory training and yoga interventions lasted 45 minutes, once a day for 10 sessions. The yoga classes consisted only of pranayama, mudras (hand positions) and mantra (chanting OM) for their known beneficial effects on cognitive abilities. Asana were not included, which may in fact increase compliance in middle-aged adults and requires less space for performance. While working memory training resulted in positive outcomes on cognitive abilities as expected, the combined yoga and working memory group (group 1) showed even greater benefits on the same measures. This may be due to the additional benefits provided by yoga practice such as increased alertness and decreased stress.
In summary, studies to date have provided preliminary evidence that yoga practice may result in improved working memory in healthy adults, even when compared to conventional working memory training tasks. Future research should address the limitations of previous studies, which include small sample sizes and lack of longer-term follow-up evaluations. It would also be important to evaluate the response of other populations such as children and individuals with known working memory deficits. Ultimately, future working memory research trials will also shed light on the relative contribution to efficacy of the different components of yoga such as physical postures, breathing techniques and meditation. Such future studies would further improve our knowledge of the underlying mechanisms of yoga in cognitive function and ideally consist of larger randomized controlled trials and more comprehensive neuropsychological batteries.