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Grow your Brain: Neurological Impacts of Yoga Practice

Abstract

Neurodegenerative diseases, such as Alzheimer’s, Parkinson’s, and Huntington's disease, are disorders characterized by the loss of neurons, often leading to dementia. Dementia is an umbrella term used to refer to progressive neurological impairments that affect thinking, learning, memory, and daily living. With no known cure for neurodegenerative diseases, interventions such as a healthy diet and regular exercise have been widely encouraged in order  to delay onset or slow progression of symptoms. Yoga is one form of physical exercise that has been shown to positively impact the neuromorphology in the brain by increasing gray matter volume and stimulating the hippocampus. The database PubMed was utilized to gather studies and peer-reviewed articles which investigated the impacts of yoga practice on the brain. Keywords such as “Yoga” and “Memory” were used to refine the most relevant articles, all of which were published from 2012 to the present. This review focuses on the effects of Yoga practice on the brain. This includes stimulation of the hippocampus resulting in lower stress levels, improvements in memory retention, and increases in gray matter volumes (GMV). These findings suggest that yoga could be a productive, noninvasive, and affordable practice for brain stimulation that could impact incurable neurodegenerative diseases. Further research needs to be conducted on which specific types of yoga practice could be used as medical treatment for neurological repair.

Database: PubMed

Timeline: 2012-Present

Keywords: Neurodegenerative Diseases, Yoga, Gray Matter Volume (GMV), Memory, Hippocampus

Introduction

Neurodegenerative diseases are characterized by neurological impairments that affect a variety of human functions. One of the most common neurodegenerative diseases is Alzheimer’s disease (AD). According to Alzheimer’s research, the neurons damaged first by AD tend to be those associated with language, memory, and thinking [24]. Another neurodegenerative disorder is Parkinson’s disease (PD), which causes muscle stiffness, tremors, and loss of coordination and balance [27]. For both AD and PD, alterations occurring in the brain are believed to begin much earlier than the onset of symptoms, making them progressive orders [11]. AD continues to be the fifth-leading cause of death among Americans 65 years and older [11]. Both AD and PD, like most neurodegenerative diseases, have no current cure, but there are ways to manage symptoms with drugs or non-drug alternatives [11].

Non-drug treatments implemented to help manage the symptoms of  age-related cognitive diseases include physical activity, music intervention, art-based therapies, memory and orientation exercises, and a heart-healthy diet. [11] Participating in these interventions could provide positive health benefits as a whole, while also supporting management of neurological disease symptoms. In particular, physical exercise has been shown to provide several wellness benefits for the brain and body. Taking all of this into account, it is unsurprising that, like other forms of exercise, Yoga has been linked to affect memory function.

Yoga is a practice that engages both the mind and body. It originated in India, but has been popularized across the world. Today, in Western culture, yoga is seen as a relaxation exercise that incorporates stretching and breathing techniques. More specifically, asanas, or postures, and pranayama, a technique to control breathing, have become the most popular yoga practices in Western culture [13]. Practicing yoga has become common in these societies due to its proposed health benefits, such as improving arthritis pain or controlling asthma. In addition to its effects on the physical body, yoga also offers relaxation, emotional stability, and peace of mind [13]. Research has shown that practicing yoga is associated with lower stress levels, as it affects the anterior hippocampal subregion, which is responsible for stress response and anxiety-related behavior [3,7]. Additionally, research has shown that yoga impacts the hippocampus and gray matter volumes (GMV). The hippocampus is a brain structure responsible for memory and learning, positioned deep in the temporal lobe. Gray matter is present in the outermost region of the brain and extends into the spinal cord. It is responsible for maintaining processing speed and transmitting sensory signals [11]. Targeting gray matter and the hippocampus could reduce cognitive decline and memory loss.

Explorations into the impact of yoga on the brain have unveiled a multitude of long-term neurological benefits. Yoga has been correlated with decreasing stress levels, as it stimulates the regions of the brain associated with stress, including the hippocampus [13]. In addition to this, yoga practice has been shown to increase GMV in the brain, improving memory, cognitive function, and mood [1-8]. In this review, we demonstrate how long-term yoga practice affects neurological function, by lowering stress levels, improving memory by activating the hippocampus, and increasing GMV to improve cognitive function, and therefore, is a tenable intervention for those at risk for neurodegenerative diseases.

Stress Levels in the Brain Impacted by Yoga Practice
The Importance of Reducing Stress Levels

Stress is an emotion of physical or mental tension. Its expression can alter an individual's thinking, decision-making, and both physical and mental well-being. As a society, we are aware of the need to reduce stress, as it affects several aspects of daily life. Research has investigated a variety of effects of high stress levels, such as hypertension and an impaired immune system [18,20]. However, research has also shown that stress levels impact cognitive function and memory, and decrease reaction time. The specific regions of the brain affected by stress are the hippocampus, glucocorticoid receptors within the hippocampus, and the amygdala, which all reside in the temporal lobe. These regions are critical in cognitive control, memory, sensation, and movement [20]. In particular, the amygdala is critical in its role of assessing the emotional aspect of memories [20]. Stress could impair an individual's memory and further heighten neurodegenerative disorders. It is crucial to be mindful of chronic stress, especially in the aging population, as it could impair neurological function and cognitive decline. 

Yoga Reduces Stress Levels

Yoga incorporates mindfulness and meditation practices that channel self-reflection and relaxation. It has been found that meditators have reduced stress levels after practicing long term yoga [3]. Reduction in stress symptoms improves memory, attention, perceptual processing speed, and cognitive control, as yoga practice engages with the regions responsible for stress and anxiety related symptoms [3,7,8]. This section will demonstrate how yoga practice reduces stress, which could suggest that continuous practice is a productive intervention for the harmful neurological effects of aging, ultimately impacting memory loss and cognitive decline.

In a recent study that investigated the impacts of yoga practice, researchers found that long term yoga practitioners that had more than 3 years of yoga practice, experienced reduced stress as a result of stimulation of  the anterior hippocampal subregion, which is correlated with emotional stress [3]. The anterior hippocampal subregion is composed of lateral (intraventricular) and medial (extraventricular) fragments. These regions provide connectivity through the brain that has been correlated with response to events and autobiographical memory [17]. Stress, specifically long-term, continuous stress, has been associated with inhibition of hippocampal-dependent memory formation, along with navigational functioning [3]. Pathological stress creates an imbalance in neural circuitry that can impede cognition by lessening inhibitory functions and weakening explicit memory formation, which is already a common decline in the aging population [7,19]. 

Although yoga has been correlated with reduced stress levels, it is crucial to compare results across different practices, because results could be too heterogeneous to make concrete claims [7]. In a meta-analysis published in 2023, researchers analyzed 49 different articles investigating the effects of Yoga practice on neuropsychiatric metrics such as stress, cognition, anxiety, and depression. For the most part, their results were too heterogeneous to make concrete statements, as there were several different types of yoga studied, including Hatha, Chair, Vini, Thai, Laughter, just asanas, and Silver Yoga. However, there was an overall consensus that stress levels were reduced in the participants who practiced yoga, regardless of type. There was an over 69% reduction in symptoms in the elderly, therefore demonstrating that physical activity plays a role in stress reduction [7].

Overall, reducing stress levels is crucial for the aging population because chronic stress affects regions of the brain such as the hippocampus and amygdala, resulting in memory loss and decline in cognitive function. Yoga has been shown to reduce stress levels as it engages the mind through meditation and activates regions of the brain such as the anterior hippocampal region, which relates to stress response. High stress levels have been correlated with central nervous system impairment, therefore reducing stress through Yoga practice could be beneficial for the aging population as they have experienced the greater effects of neurological aging. 

Long-term Yoga Practice Impacting the Brain:

The Importance of the Hippocampus

The hippocampus is one of the most studied brain structures as it is extremely important in the storage and formation of declarative memories [2]. It is a complex brain structure embedded deep in the temporal lobe and responsible for learning and memory [21]. Memory enhancement studies often focus on the hippocampus and hippocampus-associated brain structures, including the prefrontal and parietal cortical regions [2]. The hippocampus interacts with several regions of the brain, such as the entorhinal cortex (EC). The EC has received attention in research, as it is responsible for mediating information going to and from the hippocampus, making it a critical part in pattern recognition and encoding of memories [22]. In addition, the EC generates a neuronal projection in layers II and III known as the perforant pathway. Within the cells of the perforant pathway, neurofibrillary tangles are found to develop in patients with AD [22,23]. Neurofibrillary tangles block neurons’ transport system which could damage synaptic neuron communication, affecting declarative memory [24]. Overall, the hippocampus is composed of several parts that play a critical role in both the production and retention of memories. Taking this into account, stimulation of the hippocampus is extremely important for all individuals, especially the aging population and patients with neurodegenerative diseases. Yoga has been associated with improving hippocampal volume, which suggests it could be a positive neurological intervention for the progression of neurological diseases. 

Yoga Influencing the Hippocampus and Memory

As stated earlier, yoga stimulates the mind and body in ways that can provide neurological improvements to individuals who practice. This includes stimulating the brain’s hippocampal regions, which is associated with memory function [15]. This section will highlight how yoga practice impacts the hippocampus, which could provide a noninvasive way to help those suffering from neurodegenerative diseases such as AD.

The hippocampus has been shown to decrease in volume as an individual ages, prompting research on preventative measures to reduce volume loss and preserve hippocampal function [2,7, 8]. In a study conducted in 2018, researchers examined 13 long-term yoga practitioners and 13 matched-sex individuals as a control group. Examinations were done comparing magnetic resonance imaging (MRI) from both groups to study brain activity. Results showed greater left hippocampal volume in yoga practitioners than in the control group [7]. The left hippocampal subregion has been proven to have a role in verbal memory [15]. Additionally, in a study conducted in 2013, researchers compared 87 randomly selected subjects from elderly homes. 44 of the individuals practiced yoga, while 43 of the individuals were in the waitlist (non-practicing) group. Participants who showed any signs of dementia, stroke, psychosis, neurodegenerative disorders, depression, anxiety or other inabilities that prevented successful yoga practice were not included in the study, therefore the participants were relatively similar to have more comparable results. Researchers monitored each group over 6 months. Results showed that the yoga group had significant improvements in visual memory (CFT), immediate and delayed recall of verbal memory (RAVLT), executive function (Stroop interference), verbal fluency (COWA), processing speed (Trail Making Test-A) and attention and working memory (WMS-spatial span) [1]. Similarly, researchers in 2019 discovered that yoga intervention helped patients with mild cognitive impairment (MCI) carry out  activities of daily living (ADLs). Activities of daily living refers to the activities individuals fulfill daily autonomously such as eating, toileting, and bathing [27]. ADLs are associated with the development of self-efficacy, positive competence, and prospective memory for executive functions [26]. Improving performance in ADLs could reduce the effects of MCI which would be beneficial for the aging population [6]. The finding that yoga improves ADL performance suggests that yoga is correlated with reducing neurological decline. Engaging in physical activity, like yoga, is highly encouraged for all individuals, specifically those suffering from MCI or AD, as it has been correlated with improved memory and cognition by stimulating the hippocampus. Participants in these studies have shown general improvements in neurological function through yoga practice, which suggests yoga is a positive intervention for improving cognitive decline as an individual ages. 

The Importance of Gray Matter 

Gray matter is located on the outermost region of the brain and extends to the spinal cord [11]. It is composed of tissue that contains the majority of neuron somas, which are the structures that contain the nucleus of the cells. Essentially, gray matter houses a vast majority of neuron bodies [10]. Having more gray matter volume (GMV) allows for greater processing and further mental development in an individual [11].  There are many health issues that could affect GMV in the brain. For instance, in AD, when beta-amyloid protein fragments begin to accumulate in gray matter regions, they form senile plaques. These plaques interrupt neuron-to-neuron communication, causing cognitive function to decline [11]. This in turn reduces an individuals’ long-term and short-term memory. Since there is currently no cure for AD, engaging in interventions like physical activity to improve GMV could improve cognitive function and memory [4].

Improved Memory by Increasing Gray Matter Concentrations

Increasing GMV could provide several health benefits to all humans and yoga has been shown to increase GMV [4,5,8]. Research conducted on brain function has revealed that aging is correlated with diminished brain function, specifically affecting gray matter in regions of the brain such as the hippocampus, temporal lobe, prefrontal cortex and cingulate cortex [15]. Noninvasive ways to help delay decreases in gray matter concentrations could be beneficial for the aging population, specifically those with cognitive decline illness like AD. In this section, we will explain how yoga practices have impacted GMV.

In a study conducted in 2012 on Hatha yoga (a type of yoga that uses asanaspranayama and meditation) researchers compared seven Hatha yoga meditation practitioners (YMP), to seven other individuals as a control group, who were naive to both Hatha yoga and meditation. The YMP group reported engaging in active and ongoing modem Hatha yoga practice for a minimum of 45 minutes, three to four times a week, for longer than three years. The YMP group averaged 5.6 years of practice while the matched control group reported no current or past yoga practice. Through voxel-based morphometry (VBM), a neuroimaging technique, researchers discovered that YMP exhibited significantly higher GMV in various regions of the brain located in the frontal, limbic, temporal, occipital lobes and the cerebrum [5]. These regions have been correlated with cognitive control, coordination of actions, reward evaluation, and decision-making [5]. Despite noticing improved GMV in yoga practitioners, other studies have investigated yoga interventions impacting GMV and discovered no major changes from yoga practice [7]. This piece of evidence suggests that although yoga has been correlated with improved GMV, it does not directly claim that yoga causes GMV to increase. Researchers claimed that this result could have been due to the fact that their yoga intervention was only over the course of 12 weeks [7]. However observing major GMV changes has been correlated with long term yoga practice. For instance, yoga practitioners in a study conducted in 2018 exhibited greater GMV in the left hippocampal region. The researchers of this study included practitioners that had an average of 9.31 years of yoga experience. In addition, to select the groups between yoga practitioners and the control group, researchers tested physical strength and each participant's cardiorespiratory fitness to determine that the major differences in neuroanatomy were due to yoga intervention [4]. Although changes in neuroanatomy have been correlated with increasing GMV which could impact neurological function, further research must be conducted to investigate the time frame of yoga changing

the brain’s anatomy and whether it is directly caused by yoga. However, these findings suggest that long term yoga practice could improve the brain's GMV, which is associated with making fewer errors in attention, memory, and motor functions for daily activities. Future studies could investigate the neurology behind yoga intervention and its direct effects on GMV.

Conclusion

Yoga is a practice that connects the mind and body, which has been shown to provide many health benefits such as reducing hypertension, improving arthritis pain, and helping asthma. Yoga incorporates different breathing techniques, physical postures and meditation aspects that impact neurological activity. Research in this field has shown that yoga is a noninvasive way to stimulate different areas of the brain associated with stress, memory, and cognitive function.  These findings suggest that yoga could provide preventive measures for age related neurodegenerative diseases, such as AD. Further research in this field needs to be conducted to provide knowledge on which specific type of yoga practice relates to specific neurological benefits. In addition, further research needs to investigate whether long term yoga practice implemented in patients with neurodegenerative diseases could translate to real life functional advantages.

Author’s Note

I wrote this paper for a general audience with a scientific background. With aspirations to enter healthcare coupled with my passion for neuropsychology, I wanted to delve into researching neurodegenerative diseases, such as Alzheimer’s disease, because there is no cure and it impacts the lives of many individuals. Most neurodegenerative diseases are progressive disorders, meaning symptoms can often be exhibited far after the disease begins. Therefore, it is crucial to engage in preventive practices to ensure your brain remains healthy as you age. Yoga practice has been correlated with positively impacting the brain in ways that could counteract the harmful effects of aging on neurological function. Further research needs to be conducted to develop a concrete claim on whether yoga could be used as a medical intervention for neurodegenerative diseases. I wrote this paper to encourage individuals to engage in yoga practice for its neurological benefits and raise awareness for others to impact your brain while you can.

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