Episode 48: Exercise & the Hippocampus with Dr. Andrea Wilkinson
Introduction
Exercise has been shown to benefit the brain in many ways – e.g., enhanced memory, improves mood, benefits cognitive functioning, enhances brain plasticity (your brain’s ability to change itself), and augments your capacity to learn. That is a lot. Exercise has also been suggested to have an anti-depressant effect and has even been shown to counteract disease, such as Alzheimer’s disease or dementia. Exercise is powerful – and I hope that this episode will convince you that moving your body on a daily basis is a non-negotiable.
Exercise is known to have a protective effect on your brain – particularly with regards to protecting your brain cells and it also has cognitive benefits, as I’ve mentioned, pertaining to memory and learning. Researchers have often wondered why exercise is so powerful when it comes to protecting your brains against normal age-related brain atrophy or shrinkage and one key reason is that exercise has been shown to be involved in helping new brain cells grow (aka neurogenesis) in a very special part of your brain called the hippocampus.
Your hippocampus is an important part of your brain because it plays a key role in memory and learning and research shows that when we exercise we grow new brain cells specifically in your hippocampus and these new brain cells (or neurons) then get incorporated into your brain circuits improving memory and enhancing learning.
Exercise has literally been shown to increase the size of your hippocampus and improves memory.
Hippocampus
The hippocampus is a complex brain structure that is embedded deep inside of your brain, and it is the part of your brain that's important for memory and learning. It also helps consolidate your short-term memories into long term memories. The hippocampus is also important for spatial memory and it enables navigation.
Your hippocampus is plastic (meaning it changes in response to your experiences – ahem.. like exercise, and the environment) and it is a very vulnerable structure (for example it is extremely vulnerable and can get damaged by consistent [chronic] exposure to stress).
The hippocampus is one of the most extensively studied areas of the brain and when it undergoes substantial shrinkage – it can have real consequences. For example, it is one of the first areas of the brain to undergo changes in the development of Alzheimer's disease (dementia), which is the reason that one of the first signs of Alzheimer's disease is short-term memory challenges.
Research also shows, however, that the hippocampus shrinks at a rate of around 1-2% per year in older adults without dementia. This shrinkage can lead to impaired memory and is associated with an increased risk of cognitive impairment and dementia.
How can you keep protect your hippocampus against or slow age-related shrinkage? You guessed it – EXERCISE!!
The size of the hippocampus is found to be larger in older adults who exercise regularly.
Why?
But, also exercise has been linked to an increase in neurogenesis.
Neurogenesis
Neurogenesis is the growth of new brain cells. It is estimated that humans grow around 700 new brain cells each day, and exercise has been shown to increase the number of new brain cells that the human brain grows on a daily basis.
What’s really interesting is that the area of the brain that shows the most robust neurogenesis is the hippocampus.
Since the hippocampus is critical for memory consolidation and learning, the generation of new neurons and increased plasticity in this brain region may explain the improved cognition and emotional state that accompanies exercise.
In rodents, hippocampal neurogenesis as a function of exercise has been extensively demonstrated and replicated, but it is – of course – harder to measure in humans. The study of neurogenesis (the growth of new brain cells) in humans relies on more indirect measures, such as administering cognitive tests related to memory consolidation or measuring elements that are associated with neurogenesis – such as the presence of brain derived neurotrophic factor (or BDNF)
Brain Derived Neurotrophic Factor (BDNF)
BDNF is a molecule that is essential for the growth of new neurons (or neurogenesis). BDNF regulates many processes involved in neurogenesis, including the maturation and survival of the new brain cells (growing new brain cells isn’t enough, you have to connect them to your network of existing brain cells). BDNF is therefore central to brain plasticity – your brain’s ability to change itself.
Since BDNF promotes the survival of the new brain cells that you grow on a daily basis – it helps optimize how your brain cells function, improves cognitive performance and protects against neurodegenerative disease like Alzheimer’s disease.
Want to know what you can do in your everyday life to promote the production of this very special brain-derived neurotrophic factor (or BDNF)?
You guessed it – exercised!
BDNF is primarily produced during exercise.
BDNF is the key molecule involved in the relationship between exercise and hippocampal volume and higher levels of BDNF impact your cognition or mental processes. In fact, higher levels of BDNF are associated with enhanced spatial and verbal memory and recognition capabilities, and may also counteract the effects of chronic stress and cognitive decline. Furthermore, decreased BDNF levels, especially in older adults, may lead to compromised memory, neurodegeneration, and various other cognitive impairments found in Alzheimer’s disease.
So, to recap, when you exercise you increase the levels of BDNF which increases the growth of new brain cells specifically in your hippocampus (the area of your brain responsible for memory and learning). So, exercise-induced increases in BDNF are associated with both better memory function and larger hippocampal volumes.
Research: Exercise & the Hippocampus
To help illustrate the connection between exercise, increases in brain-derived neurotrophic factor, growth of new brain cells and larger memory-centres in the brain (hippocampus), I want to share a research study with you that was conducted by Erickson and colleagues in 2011.
Using 120 cognitively healthy older adults (aged 55 – 80 years).
The 120 older adults were divided equally into two groups: aerobic exercise and a stretching and toning control group.
Erickson et al. called it the “aerobic exercise” group – but, it is important to note that their exercise routine consisted primarily of walking. Participants started by walking for 10 minute at each session and increased walking duration weekly by 5-min increments until a duration of 40 min was achieved. Participants walked for 40 minutes per session for the remainder of the program.
All walking sessions started and ended with approximately 5 min of stretching as a warm-up and cool-down. Participants wore heart rate monitors and were encouraged to walk in their target heart rate zone.
For the stretching and toning control group participants engaged in four muscle-toning exercises using dumbbells or resistance bands, two exercises designed to improve balance, one yoga sequence, and one exercise of their choice. Participants were encouraged to increase the intensity by using more weight or adding more repetitions.
The brains of all research participants were scanned at the beginning of the research study (before doing any exercise sessions), at 6-months (halfway through the study) and at 1-year (after the study concluded).
Research results
The aerobic exercise walking intervention was effective at increasing the size of the hippocampus. People in the aerobic exercise walking group showed a 2% increase in the size of their hippocampus - effectively reversing age-related loss in volume by 1 to 2 years. The stretching & toning group displayed a 1.4% decline in hippocampal volume over the same 1-year period.
In the stretching and toning control group that showed shrinking hippocampus over the 1-year period, people who had a higher fitness level before the research started showed less hippocampus shrinkage over the 1-year period; so, physical fitness protects against hippocampal volume loss
These results show that the size of the hippocampus (your brain’s memory & learning centre) is modifiable in late adulthood and that moderate-intensity aerobic exercise (such as walking) is effective at reversing shrinkage. Walking as aerobic exercise protects your brain’s hippocampus and is accompanied by improved memory function.
Erickson and colleagues (the authors of this research) suggest that neurogenesis (the growth of new brain cells) and the connection of these new brain cells to other brain cells might explain the size increase of the hippocampus and the memory improvements they saw following the aerobic exercise.
A cautionary note
Remember this is just one study. I’ve done some episodes in the past about the benefits of weightlifting and resistance training on cognitive functions and how weightlifting increasing levels of BDNF in the brain. So, even though this Erickson study specifically demonstrated the benefits of aerobic exercise (walking) on brain function and structure, we know from other research that weightlifting and resistance training also plays a role in the production of BDNF and – therefore - neurogenesis. So, even though Erickson’s research didn’t show brain benefits following their stretching and toning intervention – we don’t have sufficient details of the exact toning exercises, intensity and frequency Erickson and colleagues promoted in their research and a single study is not sufficient to discount the benefits of weightlifting on brain health.
Exercise & Dementia
Regular physical exercise is an important element in overall health promotion and might also be an effective strategy to delay onset of dementia.
The biological basis for how physical exercise might preserve brain function includes improved cerebral blood flow and oxygen delivery, as well as the increasing the growth of new brain cells in the hippocampus specifically.
The general finding is that modest levels of physical exercise are associated with preserving brain structure (e.g., hippocampus), maintaining cognitive functioning (e.g., memory) and delaying the onset of dementia or Alzheimer disease.
How much should you be exercising?
The exact amount of exercise you should be doing to optimize the function of your brain and protect it from age-related structural changes is unknown. But, there does seem to be a ceiling. Extreme levels of exercise have been shown to cause more damage than good – and the best outcomes have often been linked to “moderate” exercise.
Exercise, when pursued in moderation, not only improves your physical health, but also serves to protect your brain from age-related structural changes and has been linked to prevention of numerous neurological and neurodegenerative brain diseases.
Conclusion
The research I shared by Erickson and colleagues showed that age-related shrinkage of the hippocampus (the memory and learning centre of our brain) is not inevitable and can be reversed with moderate-intensity exercise. A 1-year aerobic walking intervention was effective at increasing the size of the hippocampus in older adults by 2% and offsetting the deterioration associated with aging of this particular brain region. Because hippocampal volume shrinks 1–2% annually, a 2% increase in hippocampal volume is equivalent to adding between 1- and 2-years worth of volume to the hippocampus for this age group.
Higher fitness levels protect your hippocampus against age-related shrinkage, increases levels of brain derived neurotrophic factor, boosts the growth and survival of new neurons and enhances memory function.
The research clearly shows that aerobic exercise is neuroprotective and that starting an exercise routine later in life is beneficial for enhancing cognition and augmenting brain volume. So, get on your running shoes and start walking!