Exercising Neurons: How Working Out Can Improve Memory & Neurodegeneration

Lucas Angles

Illustrations by Natalie Bielat

As you reach the final climb of your morning run, you realize it’s happening again: you’re approaching a mental and physical limit. Your legs are turning to lead, moving slower and slower each time they hit the pavement. Your vision is clouding and your mind is completely overwhelmed by the notion of completing the path while so fatigued. Just before you give in to the prospect of relief, something strange happens. Suddenly, you begin to pick up pace. Almost magically, your vision clears, your exhaustion subsides, and you’re overcome with a sense of euphoria entering the final stretch of your route. 

 Familiar to many, runner’s high is an excellent example of how physical activity can alter our mental and emotional states. It may seem counterintuitive that exercising can modify something as abstract as consciousness. However, working out doesn’t just build up our abs and biceps — it is also instrumental to the growth and development of our brains. During exercise, your body releases endocannabinoids, biochemical substances similar to cannabis, that travel to the brain and bring about a sense of calm and improved mood [1]. While this phenomenon creates a tangible sensation — euphoria — other cognitive effects of exercise can be more difficult to grasp. Improvements in memory are not often noticed by individuals themselves, but are still very much present in those who exercise [1]. Through the substantial change in brain physiology during and after physical activity, working out can help strengthen neural communication and may offer a useful therapeutic approach to combating degenerative memory loss in the near future.

Sculpted Abs, Sculpted Brain: Exercise and Neurogenesis

For a good portion of the 20th century, the brain was considered to be an entirely static organ [1]. Because the brain’s general size, shape, and weight seemed to remain relatively constant throughout life, scientists believed that neurons — the cells responsible for transmitting and organizing our thoughts and perceptions — were unable to divide or multiply like other cells in the body. Imagine getting a paper cut and never being able to regrow the skin cells needed to close the hole: you would still be able to see the wound even years later. This is how clinicians understood patients’ difficulty in recovering from brain injuries; by conceptualizing the brain as “fixed,” neuroscientists could explain why children who had suffered from an early traumatic brain injury exhibited the detrimental effects long into adulthood [2]. In recent years, however, improvements in microscopic technology revealed that the brain is actually much more malleable than previously thought [3]. Using technologically advanced microscopes we can track the minute changes in neural tissue, including the generation of new neurons, regardless of age. One of the primary locations of this neural production, or neurogenesis, is in the dentate gyrus of the hippocampus. Considering that this brain region is the primary site for memory formation, neurogenesis here allows memory to be elastic; as we take in novel information and experiences, our new neurons quickly incorporate this material into our memories [3]. Thus, our memory can be modified by the growth and maintenance of new brain cells. 

While this neural development occurs throughout one’s lifespan, exercise, in particular, triggers the brain to generate new cells. Physical activity causes the brain to release a variety of molecules which act as the primary initiators for the generation of neurons and the expansion of brain tissue in the hippocampus [4]. These growth factors are used by the body to tell neurons and other cells within the brain to start growing and dividing [4]. Similar to the connections we make as people, these new neurons merge with other neurons with their own linkages, eventually expanding the entire neural network. When you exercise, these new connections can be integrated especially quickly. This transformation is observed most readily in the growth of neural networks in elderly people who undergo a regimen of moderate daily exercise [5]. In fact, aging individuals who exercised weekly for just one year exhibited significant increases in neuron count; this effect contributed to significantly improved scores on memory assessments [5].

Exercise not only develops and multiplies the neurons in our brain but also transforms the brain cells that support neurons: the glia [6, 7]. Glial cells, often overlooked and underappreciated, actually serve an important role in the brain; they support and modify neurons to improve neural communication as well as overall brain function. Much like an executive assistant, glia are constantly working; these important helper cells cushion the brain, ward off pathogens, and can even help neurons signal faster. Exercise seems to have a particularly useful effect on astrocytes, a type of glial cells that provide nutrients to neurons and regulate the growth and creation of neural connections. The space where direct communication occurs between neurons is referred to as the synapse. Synapses are important in the formation and maintenance of memory in the hippocampus [6]. Regular exercise has been linked to increases in astrocyte proliferation, size, and maintenance of neuronal synapses –– all of which serve to improve cognition and memory [7]. In other words, when we have more astrocytes to help neurons signal and grow, it becomes easier for us to retain and recall memories [7].

Strengthening Neural Pathways While Strengthening Muscles

Exercise further aids in the strengthening of memory through its lasting effects on the long-term potentiation (LTP) between neurons. LTP explains why the increased practice of a task, or repeated exposure to an experience, causes concrete neurological changes that can reinforce a memory. When your brain experiences an event, the respective pathway of neurons fires in order to process the incident through both sensory or emotional contexts. For example, suppose you read a page of a book many times over. Your interpretation of the letters on the page and your subsequent emotional reaction to the text’s content will consistently activate the same pathways of neurons. When firing along these pathways is increased by frequent engagement with the same page, receptors –– or small biological structures lining the outside of neurons –– activate and initiate LTP. 

In fact, LTP actually affects the shape and function of neuronal dendrites and axons. Dendrites are like the roots of the neuron; they branch from the body of the cell and receive signals from surrounding neurons. An axon is like the trunk of a tree: it emerges from the cell body and connects to neurons further down the pathway. During LTP, dendrites increase their branching, which allows them to receive more information [8]. LTP also induces branching from the axon, allowing one neuron to reach more neurons, or form repeated neural connections; this greatly improves neural communication within a particular pathway [9]. These rapid changes promote the fast formation of new memories, as improvements in communication between neurons solidify and consolidate information for future recall [10]. For instance, if you read and re-read the Harry Potter series dozens of times as a child, you can probably recall numerous scenes from the books with ease; the constant re-reading solidifies your memories of these stories. During exercise, the brain repeatedly activates the receptors related to LTP, allowing for increased neuron complexity to develop both during and after exercise [11, 12]. These adaptations bolster memory by forming new connections and strengthening existing ones [13].

Although the cognitive benefits of exercise have been observed for decades, the precise biological mechanisms underlying how exactly exercise can stimulate cell growth and LTP has yet to be identified. Just a few years ago, however, the discovery of a hormone called irisin offered some explanation for the neurological changes generated by exercise [14]. Produced during periods of moderate to vigorous exercise, irisin is released by muscle cells after repeated contractions [15]. The hormone stimulates cells to make more energy so that you can work harder for a longer period of time. Increased production of irisin stimulates the release of growth factors that generate new neurons while maturing ones that are already present. Irisin has also been found to increase the brain’s ability to initiate LTP when administered, most notably in the hippocampus, providing substantial evidence of exercise’s beneficial effect on memory [16].

Pumping Iron Props Up Memory

The impact of exercise on cellular proliferation and LTP also contributes to the body’s fight against neurodegeneration and age-related cognitive decline. While neurogenesis adds batteries to the brain’s original “circuitry,” LTP strengthens existing wires and creates new ones to enrich the circuit’s complex system of connections. When exercise creates new neurons, it also maintains and even strengthens memory; this effect is particularly useful for individuals dealing with neurodegenerative diseases which disrupt the ability to recollect information [17]. Many symptoms of such diseases, like memory loss or depression, are primarily the result of cell death; thus, cell growth can counteract any noticeable deficits caused by cell degeneration [17]. The proliferation of astrocytes can help regulate the brain’s immune response against damage and disease, as these cells help to fight off foreign invaders [18]. In neurodegenerative diseases like Alzheimer’s or Parkinson’s, it is the body’s self-defense response — not the disease itself  — that causes cell death. While attempting to destroy foreign substances that may cause the body harm, immune cells release toxic chemicals that not only destroy the offending agent, but the neurons in the surrounding area as well. When new astrocytes are generated as a result of exercise, the brain is able to initiate specific immune attacks to prohibit the destruction of healthy neurons, thereby aiding in the fight against these diseases [18]. 

As we age, our brain slowly becomes less malleable. Older brains are no longer able to support LTP and plasticity, or the processes that allow us to incorporate and utilize valuable information instantaneously. With consistent exercise, however, we can reinvigorate our brains and the LTP necessary to improve neural communication [19]. These modifications help individuals build a foundation to stave off neurodegeneration and age-related decline, simply by exerting themselves for a few minutes a day [19]. Just walking for 90 minutes a week can increase brain volume at ages when the brain typically shrinks [5]. Exploration of this phenomenon has opened new doors to a method of accessible, affordable preventative treatments in a world where healthcare costs are rising exponentially [20]. The astounding manner our bodies can affect our brains and vice versa allows us to become the electricians of our own brains. Even by just practicing occasional exercise, we have the power to modify our neural circuitry, optimizing our minds and bodies and protecting them from the threat of neurodegeneration.

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