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Running Head: EXERCISE AND MEMORY IN OLDER ADULTS 1

Memory in Older Adults: Does Exercise Make a Difference?

Sara Einhorn

University of North Texas

EXERCISE AND MEMORY IN OLDER ADULTS 2

Abstract

Older adults infamously begin to lose their memory, even outside the realm of diseases such as

Alzheimer’s or Dementia. The reasons behind this memory loss surprisingly remain elusive,

although many theories exist. Models that explain the mechanisms of memory aid in the

theoretical basis for memory deterioration. Researchers have begun to explore exercise as a

preventative method to avoid memory loss that occurs with aging and even to fend off diseases

affecting memory. Studies show mixed results that generally show exercise to have either no

effect on memory or a positive effect on memory and cognitive abilities. The type of exercise

may play into the cognitive benefits experienced, although the underlying mechanism also

remains unknown despite many theories. Due to the varied results and the many unknowns, no

conclusive evidence truly exists on how to prevent memory loss with exercise. For this reason,

future research needs to become more standardized in order to validate results that can then be

used in a practical manner.

Keywords: Memory; memory loss; older adults; exercise programs; aerobic exercise; aging


Memory in Older Adults: Does Exercise Make a Difference?

Research clearly shows that memory declines as people age so that by the time a person

reaches the ‘older adult’ stage, meaning after the age of 60 or so, memory starkly differs in

younger adults. Many examples of this well-known decline exist in jokes, TV shows, and even

birthday cards. While some diseases such as Alzheimer’s significantly impair memory at a rate

more rapid than usual, this paper focuses on more typical courses of memory decline in older

adults. What can be done to prevent or slow memory decline?

Many studies have suggested that exercise can positively affect memory in older adults.

However, results vary between studies and some studies suggest no effect. This variation in

findings results from dissimilarities amongst the variables studied including the type of exercise

intervention and cognitive measures of memory. To truly determine if exercise has a positive

effect on memory in older adults, researchers should ultimately study the same variables in

similar populations so they can generalize results and create effective interventions going

forward.

Memory Decline in Older Adults

To understand memory decline in older adults, this paper will briefly explain models of

memory. The Attkinson and Shiffrin (1968) model of memory suggests that the brain transforms

stimuli into three types of memory: sensory, short-term (STM), and long-term memory (LTM).

Sensory memory holds incoming information for only a few seconds. The brain then processes

this information into STM which it holds on to for about 15-20 seconds. To push the stimuli into

LTM, the person must practice some control processes to make the stimuli more memorable and

push focus onto it, such as rehearsal of the information. A person can recall information in LTM

from a few moments ago to decades ago (Goldstein, 2015).


Long-term memory consists of explicit and implicit memory. Explicit memory consists of

conscious recall while implicit memory consists of an unconscious recall of how to do

something. Within explicit LTM, the brain maintains episodic and semantic memory. Episodic

memory pertains to recalling personal events while semantic memory pertains to recalling facts

(Goldstein, 2015). Implicit memory contains multiple components including procedural memory,

priming, and conditioning. For example, Balota et al. (2000) make a distinction between explicit

and implicit memory noting that explicit memory involves intentionally recalling episodic events

such as dinner last night and implicit memory involves recall of riding a bike, for example.

According to Balota et al. (2000), sensory memory and STM capacity don’t vary

appreciably with age. However, in terms of LTM, age disrupts episodic memory much more than

semantic memory. This disruption can occur with encoding (the initial storage of memory),

retention, or retrieval (Balota et al., 2000). Older adults have more difficulty with creating

elaborate memories but remain on par with younger adults in terms of retention. The most

noticeable and discussed difference between age groups arises in the retrieval of memories,

depending on the type of recall. Free-recall demonstrates the largest differences, followed by

moderate differences with cued-recall, and little difference in recognition (Balota et al., 2000).

Balota et al. (2000) also note that older adults have more difficulty recalling the source of

information as compared to younger adults.

Similar to STM, Baddeley and Hitch’s model (1974) suggests something called working

memory exists. Working memory maintains a limited capacity for temporary storage and

manipulation of information used in complex tasks (Goldstein, 2015). While STM briefly holds

information, working memory focuses more on processing and manipulating information during

cognition. Working memory consists of a phonological loop, which processes verbal and


auditory aspects of language, a visuospatial sketchpad, which creates visual images in the mind

using visual and spatial information, and a central executor, which controls the focus of

attention. In the brain, the prefrontal cortex processes this incoming visual and auditory

information.

Theoretical Frameworks for Memory in Older Adults

Multiple frameworks exist to explain the decline in memory amongst older adults (Balota

et al., 2000). First, the speed of processing framework declares that all cognitive processing

slows with age, as demonstrated across multiple measures and cognitive tasks (Balota et al.,

2000; Behrer et al., 2013). Second, the theory of reduced processing resources suggests that older

adults have reduced attentional capacity and therefore have trouble with more complex tasks

involving memory, such as deep encoding mechanisms. For example, older adults encode in a

more generic fashion instead of using specific details, leading to poorer recall later. Similar to

reduced processing resources, some psychologists believe older adults have reduced working

memory capacity in terms of storage capacity and manipulation of information (Balota et al.,

2000; Behrer et al., 2013).

Since age affects some components of memory but not others, psychologists may also

distinguish between automatic and controlled processing (Balota et al., 2000). Automatic

processing requires little attentional capacity and are thus unaffected by age while controlled

processing requires intentional processing and high attentional capacity. This effort interferes

with cognitive processing and thus becomes affected by age as attentional capacity declines. In

contrast, a contextual/environmental support theory focuses on the environmental or contextual

cues provided with each task (Balota et al., 2000). If older adults have context for retrieval, the

effects of age will diminish. The opposite holds true if older adults have no context or support


with the task. This view supports little difference for semantic memory or implicit memory as

tasks require priming.

The final theory, inhibition, focuses on deficits in memory due to older adults’ inability to

inhibit processing of irrelevant information (Balota et al, 2000; Behrer et al., 2013). According to

this theory, an efficient processing system must allow relevant information to enter the working

memory while suppressing activation of irrelevant information. This theory supposes that older

adults have more trouble inhibiting the irrelevant information and thus become distracted by it.

As a result, they have a harder time with memory tasks and rely on context or easily accessible

memory instead of searching memory.

Each theoretical framework has its merits and its pitfalls, but each serves to explain some

portion of memory in older adults. Additionally, each framework draws from neuropsychological

facts as well as experiments which support each theory. No one theory perfectly addresses

memory in older adults, and thus research in this field varies. In particular, when evaluating

moderating or preventative factors, research outcomes vary due to the multiple theoretical

frameworks. Nonetheless, these theoretical models support research which generally shows that

exercise positively affects memory in older adults.

Effects of Exercise on Memory in Older Adults

Although results do not unanimously conclude that exercise positively affects memory in

older adults, the majority of studies show a positive effect. In general, studies show that aerobic

exercise and resistance training increase memory in older adults (Colcombe & Kramer, 2003;

Lachman et al., 2006; Behrer et al., 2013). In particular, aerobic exercise combined with

resistance training more greatly affects older adults than aerobic exercise or resistance training

alone.


In terms of memory functions, according to Colcombe and Kramer (2003), some research

suggests exercise would more readily impact visuospatial memory because this is more affected

by aging than verbal memory. Recall from above that visuospatial memory arises in working

memory as well as LTM. More specifically addressing the working memory, aerobic fitness

should lead to improvement in working memory because executive control functions like

working memory are susceptible to aging, (Colcombe and Kramer, 2003; Lachman et al., 2006;

Behrer et al., 2013). Lachman et al. (2006) further suggest that aerobic exercise over longer

spans of time will have better effects than shorter spans. This holds true according to Behrer et

al. (2013) who looked at studies across the globe that found reduced cognitive decline with years

of exercise.

Behrer et al. (2013) also note that aerobic fitness may aid in attentional control, meaning

older adults can better conduct complex processes of memory. According to Pontifex et al.

(2009) and Behrer et al. (2013), evidence shows that aerobic exercise improved tasks that require

attentional and executive control when exploring aerobic exercise compared to stretching and

non-aerobic exercising. This suggests that “aerobic exercise may be an important cardiac and

brain protective factor as people age” (Behrer et al, 2013, p. 3). Behrer et al. (2013) also find that

resistance training demonstrates cognitive benefits.

Like Behrer et al. (2013), many studies explore the effects of resistance training on

memory. In particular, Lachman et al. (2006) didn’t find significant differences between control

groups and intervention groups. However, the study found that higher resistance produced better

effects on memory than lower resistance. Additionally, a study by Pontifex et al. (2009) found no

cognitive benefits of resistance training compared to aerobic exercise. In this study, exercise was

acute and not longitudinal as other studies suggest is more effective for memory. Nonetheless,


Pontifex et al. (2009) conclude “the data herein indicate that the executive control of working

memory is differentially influenced by specific types of acute exercise and suggests that changes

in cognition may be specific to aerobic exercise” (p. 932). On the other hand, Behrer et al. (2013)

note multiple studies that have found positive effects on memory associated with resistance

training multiple times a week.

An interesting step in a different direction by Nishiguchi et al. (2015) explores the effects

of physical activity and a cognitive exercise simultaneously, also known as dual task activities, in

a 12-week program. Participants experienced increased efficiency in the brain and improved

memory after exposure to cognitive activities and walking exercises. Nishiguchi et al. (2015)

suggest that results may only occur for non-impaired older adults, however. The study notes that

participants in the intervention group steadily increased steps over the course of the 12 weeks,

potentially increasing the improved memory despite the relatively short time frame.

As noted above, studies overall show mixed results that tend in the positive direction. At

the very least, exercise does not appear to harm memory function and possesses other positive

health benefits. The underlying mechanism of memory improvement or maintenance has not

been identified. The study by Nishiguchi et al. (2015) alludes to some potential underlying

mechanisms of the effects of exercise on memory in older adults. However, multiples theories

exist and the sections below explain.

Proposed Mechanisms of Effects of Exercise on Memory in Older Adults

While exercise of any sort has been shown to benefit older adults’ memory, the

mechanism by which this occurs and the dose-response relationship remain unclear (Behrer et al,

2013). However, enough evidence exists to propose viable theories. After performing a review of

studies on exercise and memory in older adults, Colcombe and Kramer (2003) found aerobic


exercise induced “higher levels of activation of dorsolateral prefrontal cortex [which] were

associated with faster working memory retrieval for older adults” (p. 129).

According to Lachman et al (2006), aerobic exercise may affect memory through

increased blood flow to the brain or via insulin-like growth factor 1. Behrer et al. (2013) suggest

that cardiorespiratory fitness affects cognitive ability. Pontifex et al. (2009) similarly suggest that

evidence shows an increase in cerebral blood flow with exercise. However, animal studies

demonstrate increased blood flow occurs unevenly throughout the brain, including the

hippocampus region. Aerobic exercise may affect blood flow in the brain differently than

resistance exercises, thus accounting for the differences between the two differing effects on

memory (Pontifex et al., 2009).

According to Pontifex et al. (2009), animal studies show a positive association between

aerobic exercise and biochemicals, such as brain-derived neurotrophic factors (BDNF) and

serotonin, which increase the production of neurons. These biochemicals generate neurons in the

hippocampus of animals. Since working memory tasks involve the hippocampus, this could

explain some aspect of memory in older adults, although the details of the mechanism currently

remain unknown.

Kirk-Sanchez and McGough (2014) propose another theory that exercise reduces

cardiovascular risk factors which in turn reduces cognitive impairment or prevents cognitive

impairment. Cardiovascular risk factors such as hypertension and diabetes negatively affect

cognitive impairment. Exercising may reduce these risk factors and in turn reduce or prevent

cognitive impairment. For example, hypertension restricts blood flow in the brain and may cause

white matter disease and reduction, thus affecting brain functions including the various aspects

of memory (Kirk-Sanchez & McGough, 2014). However, studies of older adults who have


controlled hypertension report no difference in cognitive ability compared to those without

hypertension.

Insulin in the case of diabetes also affects cognitive function with age. Elevated insulin

levels can cause the release of inflammatory agents in the brain (Kirk-Sanchez & McGough,

2014). Aerobic exercise improves cardiorespiratory fitness and glucose tolerance while also

providing positive cognitive results. This outcome likely results from improved cardiovascular

function and blood flow in the brain, reduced inflammation, and improved insulin-dependent

energy metabolism.

Despite some theories, the lack of clarity and certainty in the mechanism of exercise and

memory causes some chaos in the methodology of studies exploring that subject. Therefore,

future research should explore this area further in order to create more uniform methodology in

studying the effects of exercise. Additionally, knowing the mechanism helps practitioners design

practical programs for older adults.

Methodological Issues in Studies of Exercise and Memory

While multitudes of studies exist about exercise and memory in older adults, they vary in

their theoretical frameworks as well as variables studied. Studies span the theoretical frameworks

described above, so comparison across studies can be difficult from a theoretical perspective.

Additionally, studies evaluate differing age groups, exercise intensity and length, measures used,

beginning fitness levels, gender, and cognitive tasks used (Colcombe & Kramer, 2003; Lachman

et al., 2006).

When researchers begin to enter the realm of exercise effects on memory in mildly

cognitively impaired older adults, the waters get even murkier. According to Gates et al. (2013),

no objective definition exists for mild cognitive impairment compared to normal cognitive


function. In other words, a study may exclude any older adults with a cognitive impairment but

the characteristics for this exclusion are not uniform across studies. Therefore, study populations

will not be uniform and results cannot be generalized and repeatable.

It may be difficult to find people with an impairment at the “mild” stage to include in a

study. Additionally, as mentioned above, the definition of impairment must be uniform across

studies to truly determine meaningful results when including cognitively impaired individuals. It

seems this could also present some ethical dilemmas regarding informed consent, depending on

the cognitive impairment. As a result, researchers will encounter more difficulty in recruiting for

studies. In fact, Gates et al. (2013) found that the studies they reviewed did not have large

enough samples sizes to have a high power.

In terms of study design, many studies choose cross-sectional samples, introducing some

bias, and neglecting and effects over time. Other studies are longitudinal in nature but may only

span a few weeks or months while others span 6 months or longer (Lachman et al., 2006).

Lachman et al. (2006) suggest that results may vary greatly between a three-month intervention

and a six-month intervention. Therefore, all the studies that last fewer than six months may be

missing significant results and effects, making the practical application of the research even more

difficult.

In sum, many methodological inconsistencies exist between studies. These

inconsistencies make it difficult for researchers to find conclusive evidence about the effects of

exercise on memory in older adults. As demonstrated above, results vary across studies from null

effects to benefits on memory with both aerobic and resistance exercise. Clearly, researchers

encounter issues with replicability and populations vary across studies. These variations make it

difficult to create practical and effective programs from the research findings.


Conclusion

Multiple frameworks lay out potential theories on the reduction in memory among older

adults, especially as age increases. These frameworks present varied focal points which are not

necessarily mutually exclusive, from attention control to context requirements. These theories

apply when looking to exercise as a moderating or mediating factor for memory in older adults.

Studies use any number of these theories, presenting varying results based on the theory or

theories applied. For consistency, researchers should continue to explore the validity of each

theory while studying similar populations so results can become validated as well.

Research on the effect of exercise on memory in older adults shows mixed results.

Generally, research tends to support positive effects of exercise on memory in older adults. More

specifically, older adults who exercise experience a slower decline in memory than those who do

not exercise. However, several studies show no effect of exercise or only effects for aerobic

exercise. The type of exercise may also affect memory, with resistance training and aerobic

exercise demonstrating the best results overall. On the other hand, results on resistance training

have been mixed as well.

One theory holds these mixed results may arise because of the difference in the physical

effects of exercise on the body. However, despite the many theories of decline in memory, the

true mechanism for decreased memory in older adults remains elusive still. As a result, the

multiple theories proposed proliferate as is and the research becomes fragmented. Due to the

varying theories and factors studied, results of exercise on memory in older adults may be mixed.

Although researchers have conducted studies on this topic for a few decades now, truly

conclusive results of the effects of exercise and the mechanism of these effects do not exist.


Therefore, researchers should begin to study similar variables across multiple studies to

have conclusive and generalizable results. Not that every study should be the same, but the

research needs to become repeatable and generalizable to truly establish credibility. Researchers

and practitioners can create programs for older adults that will benefit their memory once they

can combine the credibility of results with an understanding of the underlying mechanisms.

Ultimately, research needs to benefit practical applications and until researchers fix

methodological incongruences, effective programs lag or simply don’t exist.


References

Balota, D. A., Dolan, P. O., & Duchek, J. M. (2000). Memory changes in healthy older

adults. The Oxford Handbook of Memory, 395-409.

Bherer, L., Erickson, K. I., & Liu-Ambrose, T. (2013). A review of the effects of physical

activity and exercise on cognitive and brain functions in older adults. Journal of Aging

Research, 2013.

Colcombe, S., & Kramer, A. F. (2003). Fitness effects on the cognitive function of older adults a

meta-analytic study. Psychological Science, 14(2), 125-130.

Gates, N., Singh, M. A. F., Sachdev, P. S., & Valenzuela, M. (2013). The effect of exercise

training on cognitive function in older adults with mild cognitive impairment: A meta-

analysis of randomized controlled trials. The American Journal of Geriatric

Psychiatry, 21(11), 1086-1097.

Goldstein, E. B. (2015). Cognitive Psychology: Connecting Mind, Research, and Everyday

Experience. 4th ed. Belmont, CA: Wadsworth Cengage.

Kirk-Sanchez, N. J., & McGough, E. L. (2014). Physical exercise and cognitive performance in

the elderly: current perspectives. Clin Interv Aging,9, 51-62.

Lachman, M. E., Neupert, S. D., Bertrand, R., & Jette, A. M. (2006). The effects of strength

training on memory in older adults. Journal of Aging and Physical Activity, 14(1), 59.

Nishiguchi, S., Yamada, M., Tanigawa, T., Sekiyama, K., Kawagoe, T., Suzuki, M., & Aoyama,

T. (2015). A 12‐week physical and cognitive exercise program can improve cognitive


function and neural efficiency in community‐dwelling older adults: A randomized

controlled trial. Journal of the American Geriatrics Society, 63(7), 1355-1363.

Pontifex, M., Hillman, C., Fernhall, B. O., Thompson, K., & Valentini, T. (2009). The effect of

acute aerobic and resistance exercise on working memory. Medicine+ Science in Sports+

Exercise, 41(4), 927.

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