The Promise of Exercise for Healthy Ageing
At present, nearly ten percent of the worldwide population is 65 years and above. With increasing life expectancy, comes more people who experience normal ageing processes and unwelcome experiences of cognitive decline (normal confusion or memory loss that arises with ageing) and age associated neurodegenerative diseases, like Alzheimer Disease. Neurology studies published in previous years have established that aerobic exercise, nutrition, and mindfulness interventions can promote healthy ageing. A lack of exercise has even been identified as one major contributor to Alzheimer Disease (Ji et al., 2017).
Aerobic exercise has been of key interest in earlier studies, which demonstrate that such exercise leads to improvement of memory function by regenerating neural pathways within an area of the brain called the hippocampus, which plays a key role in memory and learning (Erickson, 2011). More recent studies have investigated strength training combined with aerobic exercise (Ji et al., 2017), and exercises that contain ‘mindful’ elements as well as physical elements, like yoga and Tai Chi (Yue et al., 2020; Zheng et al., 2015). By encouraging regular exercise in the older population, it may be possible to maintain or increase memory function and delay neurological changes that come with ageing. Here, we will explore how this knowledge can be used to enhance current treatments for older individuals.
The Hippocampus and Memory
The hippocampus is a part of the brain which plays an important role in several human functions, including memory and learning. A reduction in size of the hippocampus volume, alongside a reduction in the birth of new neurons, increased inflammation in this region of the brain and reduced connectivity between brain cells, has been proposed to leave adults more vulnerable to cognitive decline (Bettio, Rajendran & Gil-Mohapel, 2017). In adults around the age of 50, it has been highlighted that the hippocampus decreases in size and neurogenesis naturally declines (Hamilton and Rhodes, 2015; Raz et al., 2005).
The hippocampus is an area of the Medial Temporal Lobes (MTL), which has been established as essential for memory function, especially processing information from external stimuli, consolidation, and retrieval of memory. We will focus on the hippocampus structure within the MTL as it has received the most attention due to how it is affected in the ageing process, particularly memory, and its uncovered ability to change through our lifetime via neurogenesis and neuroplasticity. Research suggests that if we can stop the reduction in hippocampal volume and maintain or increase activity in this region, we can help reduce the risk of cognitive decline that comes with ageing.
What is Neuroplasticity?
The ability of the brain to change, rewire and adapt throughout life because of experience is known as neuroplasticity. A similar process known as neurogenesis refers to the birth of new neuron cells, which transmit information through different areas of the brain. It is estimated that 700 neurons are birthed in the hippocampus each day in middle aged adults, which steadily declines after the age of 60 (Spalding et al., 2013). Researchers have shown that the brain can maintain a remarkable level of neuroplasticity, even in older, frail individuals (Byrne, 2020), helping to avoid or delay cognitive decline. Previous research shows that increased hippocampus size in older adults is associated with higher fitness levels, through promoting neuroplasticity and neurogenesis (Cheiffi et al, 2017; Hamilton and Rhodes, 2015). This may be central to understanding memory function and is of key importance in the treatment of conditions associated with cognitive decline and dementia.
Chemicals in the brain known as neurotransmitters play a crucial role in plasticity and regeneration. Neurotransmitters are chemicals which fire from one neuron, along a synapse to another cell which may be a neuron, a muscle cell, or a gland cell. Brain Derived Neurotrophic Factor (BDNF) is used as an indicator to measure how well neurotransmitters are working (Bathina & Das, 2015).
Aerobic Exercise and Memory
At the University of Pittsburgh, a study was conducted to compare light exercise to aerobic exercise. Older adults were studied who participated in weekly moderate intensity aerobic exercise and compared to a control group who engaged in gentle stretching and muscle toning exercises over one year (Erickson et al., 2011). A medical imaging technique called Magnetic Resonance Imaging (MRI) was used to visualise brain regions at the start, six months on and at completion. The memory of participants was assessed and serum BDNF levels were measured.
Results showed growth in the hippocampus (2.12% growth in the anterior left hippocampus and 1.97% growth in the anterior right hippocampus) in the group that participated in weekly moderate intensity aerobic exercise. However, the control group experienced 1.4% volumetric decrease. Both groups showed an increase in spatial memory. However, increased quantities of serum BDNF during the study was linked with greater hippocampal volume in the aerobic exercise group, but not improved memory function. This implies other factors mediated this response. Focusing on BDNF alone does not illustrate the whole process of neuroplasticity and neurogenesis within the hippocampus because there are a myriad of neurotransmitters involved in synaptic plasticity (Autio J et al., 2020).
Tai Chi and Memory
Exercising the body in old age has been found to improve memory and decrease the risk of cognitive decline. A growing number of more recent scientific studies have shown that incorporating mental stimulation and focus into exercise can harness the neuroplasticity benefits gained from physical activity (Ji et al., 2017; Yue et al., 2020). A recent study by Yue and colleagues (2020) compared a group of older adult participants who practised Tai Chi to a control group, who exercised solely by walking. It was found that the Tai Chi group exhibited higher levels of grey matter density (GMD) in regions of the hippocampus associated with memory functions, particularly memory of every day events.
Grey matter processes and sends information to various parts of the body and is significant because greater GMD is associated with increased function throughout the brain. Yue et al. (2020) concluded that individuals who regularly participate in exercise that involves a strong cognitive (mindful) element, may gain superior benefits in their exercise practise. This study mirrors earlier findings that have demonstrated movement is beneficial to the brain and incorporating mindful elements that encourage increased activity in the brain is even better (Zheng, 2015). The study concluded that practising Tai Chi was more effective in enhancing memory rather than regular walking exercise.
Opportunities for Further Research
Analysis of 15 studies confirmed up to a 38% reduced risk of dementia in individuals vigorously exercising more than three times a week (Sofi et al., 2011). However, a growing recognition of mindfulness interventions paired with exercise holds significant hope for the future. The answer to the ageing brain may be found in yoga classes and mindful walking among other forms of mindfully moving the body. There are likely to be indirect effects impacting brain structure and memory from the exercise intervention, for example via improved stress management, improved sleep, dietary changes, and reduced risk of heart diseases. Taking a blended approach in neurological research may offer a greater understanding of the process and treatment of ageing. Further, it is important to investigate other adaptations that can be used in parallel to reduce cognitive decline, such as social interaction (Zheng et al., 2015), cognitive training (Bherer, 2015) and sexual activity, (Wright et al., 2017). Studies show that stress restricts neurogenesis within the hippocampus (Paizanis et al., 2007), therefore managing stress, particularly chronic social stress is crucial to encourage healthy ageing (Fuchs E & Flügge G, 2014).
Conclusion
What can we do in older age to prevent cognitive decline, and what can health professionals advise the public? The results from Erickson et al. (2011), indicate that aerobic exercise is neuro-enhancing, thus can improve cognition. Further, where exercise is cognitively demanding (e.g during Tai Chi) the benefits are enhanced. Future studies using functional MRI, measuring GMD, and investigating activity of other neurotransmitters are needed to better understand what conditions encourage neuroplasticity and neurogenesis to reduce age‐related cognitive decline and neurodegenerative diseases. A holistic approach incorporating other behaviour adaptations including meditation, stress reduction and appropriate social interaction as well as exercise, is likely to enhance improvements in brain function to encourage healthy ageing, alongside continuing advancements within pharmaceutical research.
Glossary
Brain Derived Neurotrophic Factor (BDNF): Used as an indicator to measure how well neurotransmitters are working.
Cognitive decline: The decreased speed at which the brain functions over time, sometimes leading to memory loss or confusion.
Grey Matter Density (GMD): Tissue in the brain which processes and sends information to various parts of the body.
Hippocampus: Area of the brain which plays an important role in several human functions, including memory and learning.
Medial Temporal Lobes (MTL): Area of the brain associated with sensory, emotional, motor, memory, and higher reasoning. The hippocampus is located within this region.
Neurogenesis: The birth of new neurons in the brain.
Neuron cell: A type of cell that exists in the brain and operates as messengers between different parts of the brain.
Neuroplasticity: The ability of the brain to change and adapt in structure throughout life because of experience.
Neurotransmitters: Chemicals which fire from one neuron, along a synapse to another cell which may be a neuron, a muscle cell, or a gland cell.
Spatial awareness: Being aware of your surroundings and your position relative to them.
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