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Cardiovascular Exercise Improves Memory
Wei-Hsun Hsu and Len Kravitz, Ph.D.

Article Reviewed:
Roig, M., Nordbrandt, S., Geertsen, S.S., and Nielsen, J.B. (2013). The effects of cardiovascular exercise on human memory: A review with meta-analysis. Neuroscience and Biobehavioral Reviews. 37(8), 1645-1666.

The scientific effects of cardiovascular exercise have consistently focused on health benefits (Ahiskog et al., 2011), such as with disease prevention of coronary heart disease, type 2 diabetes, hypertension, some cancers and other chronic diseases. Other cardiovascular research has examined the consequences of this mode of exercise on reducing stress, depression and anxiety (Ahiskog et al). With brain function and cardiovascular exercise, much of the prevailing understandings from the research have focused on specific outcomes such as decision-making, attention, and speed processing (Roig et al., 2013). Roig and colleagues continue that recent research has begun exploring the neurobiological mechanisms triggered by cardiovascular exercise on memory processing, which will be highlighted in this research column.

What are different types of memory?
The two types of memory studied in the research are short-term and long-term. Short-term memory, also called working memory, involves information retention over a brief period of time lasting a few seconds to 1-2 minutes (Roig et al., 2013). As information comes in, the brain begins processing it immediately. Examples of short-term memory tasks from the research include memorizing a series of random digit numbers (0-9), remembering pairs of words, recalling a list of words presented orally, and/or recalling names associated with people or pictures (Roig et al). Short-term memory tests involve an almost instantaneous retention. Other subdivisions of short-term memory are introduced in the findings presented in the acute cardiovascular exercise and short-term memory section.

In contrast, long-term memory research involves the retention of memory with a delay greater than 2 minutes from exposure of the information stimulus (Roig et al). For instance, long-term memory tasks from the research include identifying 18 photographs of faces presented 30 minutes earlier, recalling details of a short history story 30 minutes after reading, and/or recollecting images presented visually 15 minutes before (Roig et al.).

Scientists further categorize long-term memory as either declarative or nondeclarative (Squire, 2004). Declarative memory refers to memories that can be consciously recalled such as facts and events. Declarative memory involves one memory system in the brain (and the brain has several). An example of declarative memory would be remembering specific news facts about events occurring around the world. Nondeclarative memory suggests that several memory systems are involved in the retention of memory. This type of memory includes previous experiences, which aid in the performance of a task without conscious awareness. Skills such as riding a bike and tying a shoelace involve nondeclarative memory. Squire suggests that all of the memory systems in the brain operate together to support our behaviors.

What are the effects of acute cardiovascular exercise on short-term memory?
Commonly, researchers use brisk walking, cycling or running in cardiovascular exercise and memory research. The acute (or immediate) effects of cardiovascular exercise on short-term memory involve the use of submaximal to maximal bouts of exercise. Although results vary from study to study due to numerous research design differences, the data indicate that acute bouts of cardiovascular exercise improves visuospacial short-term memory more so than verbal-audio (i.e., listening) short-term memory (Roig et al., 2013). The visuospatial memory includes visual perception of spatial relationships among objects, such as interpreting directions on a map. The research suggests that walking is the most effective mode of acute cardiovascular exercise to improve short-term memory (Roig et al.). In addition, the effects of acute cardiovascular exercise on short-term memory are better when the exercise bout is less than 20 minutes, and performed at a low-intensity (<40% of heart rate reserve, such as brisk walking). Fitness level does not impact the effects of acute cardiovascular exercise on short-term memory (Roig et al). Alas, the short-term memory of young adults (18-24 years of age) tends to be most positively influenced from acute cardiovascular exercise (Roig et al). Roig and colleagues summarize that acute cardiovascular exercise improves short-term memory by priming the molecular processes involved in the encoding (i.e., conversion) and consolidation of newly acquired information.

What are the effects of long-term cardiovascular exercise on short-term memory?
The effects of long-term (>6 months) cardiovascular exercise on short-term and long-term memory are different, and thus presented in two sections. Long-term cardiovascular exercise improves verbal-audio short-term memory (e.g., listening to lectures, engaging in group discussions, listening to audio books on tape). The combination of walking, running and cycling maximizes the effect of long-term cardiovascular exercise on short-term memory. Long-term cardiovascular interventions of exercise involving medium duration (20 to 40 min) and light to moderate (40 to 59% heart rate reserve) intensity show the greatest effect on short-term memory. Once more, young adults show the greatest gains of short-term memory after long-term cardiovascular exercise.

What are the effects of long-term cardiovascular exercise on long-term memory?
Long-term cardiovascular exercise initially appears to have only negligible positive effects of any sub-category of long-term memory (Roig et al., 2013). Further investigation of the literature suggests that long-term cardiovascular exercise may meaningfully delay some age-related memory impairment changes. Erickson and colleagues (2011) conducted a yearlong study with 120 male and female adults (ave age = 66yrs), none of who were diagnosed with dementia. Sixty subjects served as a control group and did stretching exercises 3 times a week. The experimental group engaged in cardiovascular walking exercise 3 times a week that gradually worked up to 40 min per session.

The walkers progressively increased their walking intensity from 50% to 75% of heart rate reserve during the course of the 12 months. Magnetic resonance imaging of the brain was completed at the beginning, middle and after one year of the intervention. Researchers were particularly interested in the effects of exercise on deterioration of the hippocampus in the brain. The hippocampus is located in the medial temporal lobe of the brain and forms part of limbic system. It consolidates new information from short-term memory to long-term memory and is associated with visuospatial memory, learning and emotions. Deterioration of the hippocampus in the brain leads to memory impairment in late life. Erickson et al. showed that progressively increasing duration and intensity of cardiovascular exercise increase hippocampal volume 2% over the course of the year. The stretching control group showed a 1.4% decline over the same time period, which was explained by the authors as a normal expected decrease with aging.

The authors propose that the increase in hippocampus size translates to an improvement in memory function, and theoretically helps to reduce the risk of cognitive impairment. The authors also highlight that the extent to which cardiovascular exercise can modify the size of the hippocampus in later life is currently unknown. Finally Roig et al. (2013) add that the research indicates that study subjects with at least an average fitness level have the best long-term memory gains from their participation in regular cardiovascular exercise.

Summary Memory Thoughts
Short-term memory and long-term memory are distinct and yet complementary to each other. Acute cardiovascular exercise (low intensity less than 20 minutes) appears to facilitate a person's short-term perception of spatial relationships tasks, such as a personal trainer re-arranging the exercise equipment in a fitness facility to adapt to client traffic flow and usage. Long-term cardiovascular exercise appears to improve short-term memory and prevent deterioration of the hippocampus. Thus sustained long-term cardiovascular exercise may delay memory impairment often observed in latter life. This new research supports the philosophy that the road to improved memory health has no finish line.

Side Bar 1. Three questions on dementia
1) What is dementia?
Dementia is the loss of mental abilities over a period (Kwak et al., 2008). It is often severe enough to interfere with a person's ability to perform daily activities. People with dementia may have trouble in learning new things, remembering names, and may have changes in behavior. They may experience irritation if they fail to complete a task (Kwak et al.).
2) Can exercise reduce the effects of dementia?
There is a growing body of research that shows cardiovascular exercise may be a useful strategy in delaying the loss of functional independence and dementia (Ahiskog et al., 2011). Ahiskog and colleagues continue that brain cognitive networks display improved functionality after 6 to 12 months of consistent cardiovascular exercise.
3. How much exercise is needed to attain these neuroprotective effects on dementia?
The exercise parameters suggest that approximately 150 minutes per week of cardiovascular exercise in 20-30 minutes bouts at an intensity of 60% of heart rate maximum is sufficient (Ahiskog et al., 2011).

Wei-Hsun Hsu is an Exercise Science undergraduate student at the University of New Mexico, Albuquerque. He is interested in pursuing a career in Occupational Therapy.
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and American Council on Exercise Fitness Educator of the Year.

Additional References:
Ahiskog, J.E., Geda, Y.E., Graff-Radford, N.R., and Peterson, R.C. (2011). Physical exercise as a preventive or disease-modifying treatment of dementia and brain aging. Mayo Clinic Proceedings, 86, 9, 876-884.
Erickson, K. I., Voss, M.W., Prakash, R.S., Basak, C. et al. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences of the United States of America, 108, 7, 3017-3022.
Kwak, Y.-S., Um, S.-Y., Son, T.-G., and Kim, D.-J. (2008). Effect of regular exercise on senile dementia patients. International Journal of Sports Medicine, 29, 471-474.
Squire, L. (2004). Memory systems of the brain: A brief history and current perspective. Neurobiology of Learning and Memory, 82(3), 171-177.