The Impact of Exercise on the Memory Function

As part of my Anatomy and Physiology class, we wrote various research papers. This one is about exercise and memory function. I have an avid love for physical exercise so it was super interesting to research and gain more knowledge about the benefits of committing to an active lifestyle. This paper covers an introduction to this topic, the specific medical background memory and cognitive abilities with increasing age and some different perspectives when it comes to aerobic exercise.

Abstract: 

The brain is the highest functioning, most important part of the human body. With connections to all muscles, organs, and other bodily functions, the nervous system is one of the most delicate and complicated networks to understand. The brain is a command center for receiving incoming sensory information and sending outgoing messages in reaction to different signals from neurons. There are many different divisions within the central and peripheral nervous systems but there are also distinct sections and parts of the brain that each have unique abilities and jobs. Some of those areas are the thalamus, hippocampus, limbic system, each of which play a role in both short- and long-term memory. As people age, the brain shrinks and changes, sometimes resulting in loss of special memories, inability to perform basic everyday tasks, and remembering specific details. Exercise has been one of the most researched options to help offset the effects of an aging brain. The more physical activity done at a later age, the more likely they are to experience a healthy mind and body. This review will discuss the potential benefits of exercise on cognitive function with increased age and some of the challenges that could inhibit exercise from being a helpful resource. 

Keywords: brain, exercise, cardiovascular, memory, nervous system, hippocampus, dementia, Alzheimer’s Disease, cognitive function

                                                                                                            Word count: 1,820

Introduction: 

It is well known amongst the medical field that exercise has numerous benefits to the human body, within the skeletal system, muscular system, and in this case, the nervous system. Exercise is an efficient, enhancement method for neurocognitive protection with increased senescence (1). For many people, exercise is a drug. It can be used to help promote health in many ways, allowing for lifestyle changes that can benefit both the individual and the people around them (2). Acute exercise is important for physical and mental health, memory function and other cognitive functions (3). Physical activity moderates decline in cognitive functioning that is associated with aging. One of the main things that deteriorates with age is fluid intelligence which is connected with information processing, short-term memory, and abstract thinking (4). Physical exercise sustains cerebral blood flow and nutrient supply that facilitates neurotransmitter metabolism and its effects on late adulthood are the strongest of any age group (4). There are many different parts of the brain that function to maintain the body’s ability to perform various physical and cognitive functions. One of those areas is the hippocampus which begins to shrink in late adulthood, leading to impaired memory and increased risks for dementia and other neurodegenerative diseases (5). This review will discuss whether or not exercise improves cognitive function, where the gaps lie in the research conducted thus far, and what might be some possible future studies in regards to preventing memory loss through exercise and other methods and using more diverse samples. 

Does physical exercise help improve memory and cognitive functions? 

The world population is growing increasingly older with every passing year, so it is incredibly important to have accessible physical activity opportunities with minimal side effects for an older generation with aging brains (5). The timing of exercise and memory stimulus plays a role in exercise-memory function. Research shows that acute intervals of exercise done shortly before memory tasks are completed leads to better episodic memory. Episodic memory is the retrospective recollection of information in a spatial-temporal context that is important for communication (6). It is also noted that acute exercise, such as cycling, is better for long term memory especially if it is performed before memory encoding moments (6). 

            There are many types of exercise that can help maintain a healthy brain. One of them is aerobic exercise, which according to the Cleveland Clinic, is any type of exercise that involves oxygen, also known as cardiovascular exercise, such as biking, running, or swimming (7). Aerobic training improves aging brain’s resting functional efficiency in higher cognitive network. Moderate exercise enhances the functional connectivity between different regions of the brain (5). Aerobic exercise increases the size of the anterior hippocampus, the grey and white matter in the prefrontal cortex of older adults as well as cerebral blood volume and perfusion of the hippocampus (5). The hippocampus is located in the temporal lobe and is responsible for neurogenesis, and functions in learning abilities, memory capacity, spatial navigation, and emotional behaviors (16). The hippocampal region and medial temporal lobe volumes are larger and higher in more fit adults (5). The increased hippocampal area is also associated with greater serum levels of brain derived neutrophic factor (BDNF), a protein which is a mediator of neurogenesis in the gyrus. (5). Increased levels of BDNF in the hippocampus are associated with better memory function. The grey matter in the prefrontal cortex is unmyelinated fibers and cell bodies whereas the white matter is the myelinated fiber tracts (8). People lose 15% of their cerebral cortex and 25% of white matter between the years of 30-90 (9). Participation in aerobic exercise programs show an increased volume of gray and white matter in the prefrontal and temporal cortices (10). Many of the benefits of exercise have been documented in small animals like mice, which are much easier to perform invasive brain observations on (11). Things like wheel running and treadmill training are shown to improve spatial learning and hippocampal neurogenesis in mice (11). Exercise in mouse models who suffered from Alzheimer’s disease (AD), showed improved, positive results. (12). Exercise in humans, therefore, has shown to improve physical, cognitive and behavioral function in patients with dementia and Alzheimer’s (12). 

Very little is known about how much the brain actually structurally changes but research studies on non-human samples have shown that aerobic exercise can lead to growth of new capillaries, increase in longevity, and the number of dendritic connections between neurons (10). Animal models have shown a link between cardiovascular exercise and the central nervous system, where cellular and molecular cascades and increased levels of neurotrophic factors, serotonin, capillary density and neurogenesis all help to create a very adaptable brain (9). Cardiovascular aerobic exercise is associated with better cognitive function in aging humans, especially with memory, and being able to switch between tasks. (10). It reduces the risk of dementia in midlife showing better cognitive scores 6-12 months of exercises compared to sedentary controls. After one year of aerobic exercise in a large, randomized control trial of seniors, larger hippocampal volumes and better spatial memory was seen throughout the participants(1). Cardiovascular fitness in gray matter is the greatest in the prefrontal cortex, the superior parietal and temporal cortices while aerobic exercise in white matter improves the anterior and posterior tracts that run between the frontal and posterior lobes (9). The more physical exercise done, like walking for example, the greater the amount of grey matter volume and therefore less risk for cognitive impairment (13). Dementia, a neurocognitive disease that reduces a person’s ability to remember names and numbers, poses a great threat to the aging world population (1). There is no medication that has proven to reduce the risk of this disease and other cognitive impairments (1). The brain shrinks 1-2% annually in adults who suffer from dementia. (5). Instead, cardiovascular fitness exercises and their relationship to brain volume changes is shown to help lessen the effect of the early stages of dementia (12). Physical activity also helps reduce the risk of incident Alzheimer’s disease by 30% (14). 

One of the biggest challenges of studying exercise on the brain, is effect of reverse causality. This is when people have better cognitive health, they can perform better during physical exercise (14). This makes it difficult to measure the exact variables that effect cognitive functions (14). While exercise proposes great benefits to the nervous system, it also can pose threats to people with significant medical conditions (1). Some people are limited to how much, if any, exercise they can do so other options like dietary adjustments and cognitive games for maintaining memory are necessary to explore in further research. Exercise can result in orthopedic injuries, increase the risk of falls, and induce heart problems (1). Since it is hard to know the proper duration and intensity of recommended exercise, it is important to consult with a medical professional first before beginning exercise if there is no previous experience or the individuals suffers from other medical conditions (1). 

Missing Information and Experimentation on the Structure of an Aging brain

Until recently with the addition of the MRI, methods for assessing brain structure changes with increasing age have been very invasive and expensive so the majority of research is done on non-human samples (S, K, Paige). While MRI’s are significantly better for research purposes and viewing the brain, it remains a very expensive option for means of experimentation. Another gap is that there has been limited research with longitudinal studies over long periods of time to show how much the brain structure changes with less or more exercise (Erikson, Raji). Those older adults with lifelong exposure to cardiovascular exercise, do show better preserved brains and have higher functioning frontal and parietal lobes but we do not know how different forms of exercise influenced their memory and cognitive health (S, K, Naftali). The measurements of exercise parameters have not been set. Most of them are not the same across different research trials and different methods such as walking, gym workouts, playing basketball, and shoveling snow all require different levels of exertion and inhalation of oxygen (1). This leads to different levels of cardiovascular exercise which in turn would lead to suggest that there are various levels of cardiovascular health. How much oxygen is sufficient and how high a heart rate should get is not conclusive amongst different trials (1). 

Future Developments for understanding the role physical activity plays in memory

            While exercise has shown to be beneficial, more research is needed to investigate the potential for fitness to reduce the risk of the brain tissue loss during modes of intervention (10). Many of the research studies which are done on the effect of exercise on the brain, are very small, select samples so in future studies, a bigger, more randomized sample size would be beneficial. It would show the neuropsychological changes between the brain volume and the cognitive changes across a more diverse selection of people (10). Future research is also needed to determine how aerobic fitness, diets, and cognitive training work together to improve cognitive functions which how this multilevel intervention could be used as a powerful tool to maintain nervous system health (9). There are some other methods such as antioxidant supplementation and cognitive training regimens that could be potential enhancers of memory and other brain functions (9). Researching other learning-based strategies that may also improve memory along with exercise would be particularly advantageous for people who struggle with physical disabilities (3). There is also the additional factor of timing, intensity, and duration of exercise that all affect the prevention of memory loss and other neurocognitive diseases (3). 

Conclusion: 

Exercise is a great way to promote a healthy brain, body, and mind. There are so many opportunities to explore prevention methods through exercise by examining different types of exercise like swimming, running, and cycling. Memory and cognitive functions can be serious challenges but using exercise as a prevention method for diseases like dementia and Alzheimer’s has proven to be successful. Aging causes changes in the hippocampus that can lead to cognitive decline such as difficulty learning new tasks in older adults (11). Exercise has become one of the best prevention methods to help limit the deteriorating consequences those diseases. (11). Research shows that older adults who exercise frequently throughout their life had significantly less brain tissue loss than individuals who lead a more sedentary lifestyle (11). With frequent, moderate intense exercise, 39% of middle-aged people, and 32% of late adults, were noted to have reduced mild cognitive impairment (15). These statistics just go to show how important it is to maintain a healthy level of exercise throughout the lifespan in order to help prevent the decline in mental and cognitive functions. Exercise is beneficial and is highly recommended to be incorporated into the everyday lifestyle but with the adherence of medical professionals who can determine the level and type best fit for each individual. 

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