Category Archives: Exercise & cognition

Reverse the Impact of Stress on the Brain with Exercise

Posted on January 9, 2020 | Leave a comment

Departing the 2010’s, feelings of stress and worry among Americans were the highest they had been all decade and among the highest in the world [1]. I doubt that drops any jaws. We are a bit obsessed with stress – many trying to rid ourselves of the brute through everything from mindfulness and meditation to yoga retreats and medication. I love the work by Dr. Susan David, who has concluded that all of this energy expended to ‘rid ourselves of stress’ can actually make a person more stressed (dubbed type II stress). Oh, the irony!

Stress is an inescapable aspect of our lives, and it is undoubtedly useful in short-term fight-or-flight situations, helping us better mobilize resources like glucose and oxygen. It’s the prolonged and unrelenting variety of stress that comes at a cost to the brain. In particular, a robust field of research has found that chronic stress shrinks the hippocampus [2, 3]. This region has long been implicated in learning and memory hippocampus_free licensure(episodic & spatial) [2, 4]. As a powerful illustration, atrophy in the hippocampus is the hallmark of Alzheimer’s disease. It is one of the most susceptible brain regions to cell death, and it may be particularly vulnerable to the impact of long-term stress because it has a high concentration of cortisol receptors [5].

So, that’s the bad news. Here’s the good: because the hippocampus exhibits so much adaptive plasticity, the effects produced by chronic stress are largely reversible. Better still, there is a free and readily accessible intervention that can dampen and even reverse these effects. I’ll give you one guess.

Most people have an anecdotal appreciation for the benefits of exercise on stress and get a feel-good buzz after a bout of exercise. What is often underappreciated is that exercise reaps very tangible anatomical and physiological benefits to the brain.  Cue my favorite study [6].

One hundred and twenty older adults were recruited and randomly assigned to 3 days a week of either moderate-intensity aerobic exercise or stretching/toning (control).*  After one year of this intervention, MRI scans showed a 2% increase in hippocampal volume for the aerobic exercise group (see graph)[6]. Exercise grew brains. Unsurprisingly, but still remarkably – the  hippocampal growth corresponded to improved memory function.

Erickson_graph 6.35.41 AM

Notice in the figure how the red line (stretching/control group) slopes down? These data support previous research showing a 1-2% decline in hippocampal volume each year in older adults, free of dementia [8]. That trajectory is inverted with the exercise group (blue line). Getting out the door for a walk 3 days a week effectively reversed age-related loss in the hippocampus by 1 to 2 years. Powerful stuff, exercise.

Now, back to stress. While there haven’t been any exercise interventions in people that look specifically at reversing the effects of stress, it doesn’t take a huge leap of fate to connect the dots here. We know chronic stress shrinks the hippocampus while exercise grows it.** Still, I like to be persuasive, and findings from a recent study in mice is just that.

Researchers at BYU had one group of mice run on wheels (covering ~5k day), while the other group remained sedentary [9]. Half of each group was also exposed to stressful situations – swimming in cold water or walking on an elevated platform. They then looked in the hippocampi of mice to assess a process called long-term potentiation (LTP). Memory formation and recall are most effective when connections between neurons are strengthened over time. LTP is a measure of this connectivity, and ultimately memory.  In the sedentary group, researchers found chronic stress weakened the synaptic connections between neurons, decreasing LTP. The mice allowed to run while exposed to stress had significantly higher LTP, and they performed better on a memory test (radial arm maze) [9]. The research team concluded, “exercise is a viable method to protect learning and memory mechanisms from the negative cognitive impact of chronic intermittent stress on the brain.”

In terms of how exercise supports the hippocampus – we believe it is a combination of increased blood flow to the brain and hippocampus [10] as well as through increased production of BDNF [6, 9, 11]. Brain derived neurotrophic factor (BDNF) is essentially a growth factor for neurons…miracle grow for brain cells.

Ridding ourselves of all the stressors in our lives is not a particularly practical option for most of us. Yet, the negative toll that stress can take is not a phenomenon beyond our control. I think that is downright empowering. So, transitioning into this next decade, resolve to move for your physical health, move for your mental health, and move for your brain health.

*Noteworthy – both groups in the study attended the same number of exercise sessions and therefore had an equal amount of social interactions. This is important because human interactions also have very real benefits on brain function [7] and may be less frequent in the older adult population.  In other words, exercise appears to protect our brains in a way that other interactions cannot. This appears to be true, even if you start moving in your 70s.

**Aerobic training grows brain regions other than the hippocampus. Another exercise intervention in older adults found increased gray and white matter volume in the prefrontal cortex after 6-months [12]. This region is instrumental to executive control functions.

References

[1] Chokshi, N. (2019, April 25). Americans Are Among the Most Stressed People in the World, Poll Finds. The New York Times.  Retrieved from https://www.nytimes.com/2019/04/25/us/americans-stressful.html

[2] Conrad, C. (2010). A critical review of chronic stress effects on spatial learning and memory. Prog Neuropsychopharmacol Biol Psychiatry 34(5): 742-755.

[3] Conrad, C. (2008). Chronic stress-induced hippocampal vulnerability: the glucocorticoid vulnerability hypothesis. Reviews in Neurosciences 19(6): 395-411. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2746750/

[4] McEwen, B., Nasca, C., Gray, J. (2016) Stress effects on neuronal structure: hippocampus, amygdala, and prefrontal cortex. Neuropsychopharmacology Reviews, 41, 3-23.

[5] Kino, T. (2015). Stress, glucocorticoid hormones, and hippocampal neural progenitor cells: implications to mood disorders. Frontiers in Physiology 19. https://www.frontiersin.org/articles/10.3389/fphys.2015.00230/full

[6] Erickson et al. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108 (7): 3017-3022.   

[7] Hari, R. & Kujala, M. (2009). Brain basis of human social interactions: from concepts to brain imaging. Physiological Reviews, 89, 453-479.

[8] Raz N, et al. (2005) Regional brain changes in aging healthy adults: General trends, individual differences and modifiers. Cereb Cortex, 15, 1676–1689.

[9] Miller, R. et al. (2018). Running exercise mitigates the negative consequences of chronic stress on dorsal hippocampal long-term potentiation in male mice. Neurobiology of Learning and Memory, 149. DOI: 10.1016/j.nlm.2018.01.008

[10] Burdette J., et al. (2010) Using network science to evaluate exercise-associated brain changes in older adults. Front Aging Neurosci 2:23.

[11] Vaynman S., Ying Z., Gomez-Pinilla F. (2004) Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition. European Journal of Neurosciences 20:2580–2590.

[12] Colcombe S., et al. (2006) Aerobic exercise training increases brain volume in aging humans. J Gerontol A Biol Sci Med Sci, 61, 1166–1170.

 

 

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Posted in Exercise & cognition, Exercise & mental health, Memory, Stress & anxiety

Claims that exercise while expecting might boost brain development

Posted on November 15, 2013 | 3 comments

We’ve come a long way from the days when obstetricians advised women to take it easy during pregnancy.  Today, healthy expecting mothers are encouraged to stay active for reasons ranging from decreased back pain and sleep problems to easier post-partum recovery and reduced risk of child obesity.  Now there is preliminary research to suggest that exercising during pregnancy might even give your child’s brain a jump-start on development.

As reported at last week’s Society for Neuroscience (SfN) annual conference, researchers from the University of Montreal randomly assigned women at the start of their second trimester to either an exercise or a sedentary group.  Women in the exercise group were told to perform at least 20 minutes of aerobic exercise three times a week at a moderate intensity.  Although, the study abstract notes that women in this group went well beyond the 60-minute per week minimum and exercised an average of 117 minutes each week.

A mere 8 to 12 days after delivery, researchers invited all mothers and their newborns back to the lab. Babies were fitted with specialized caps made up of soft electrodes that detect electrical activity in the brain (a tool called electroencephalography (EEG)). Scientists waited for the newborns to fall asleep on their mother’s lap and then monitored how their unconscious brains responded to both familiar and novel sounds – a proxy for auditory memory.

“This is important to look at at this stage in their development, because the ability to discriminate sounds is the basis of learning to speak and to understand the sounds around you,” notes Elise Labonte-LeMoyne from the research team.

The researchers reported that the babies whose mothers had exercised exhibited more mature patterns of cerebral activation. They also suggested that this could indicate their brains are developing more rapidly. The study’s lead researcher, Dr. Dave Ellemberg said in a statement, “We are optimistic that this will encourage women to change their health habits, given that the simple act of exercising during pregnancy could make a difference for their child’s future.”

Before the media gets ahold of this news and conveys the message to expecting mothers that they can exercise their unborn children straight to the Ivy Leagues (woops, too late!), there are some important limitations to emphasize about this initial research. Although the findings were presented at the reputable Society for Neuroscience’s (SfN’s) annual meeting, the methods and findings have not yet undergone the rigors of a peer-review, and have not yet been published in a journal.

Hence, it’s difficult to really assess the quality of this work, as well as its generalizability.  Among other things, we know little about how scientists monitored or determined exercise intensity in the exercise group. It’s also not clear how sedentary the “sedentary” group really was. Did the women exercise up until delivery? We’re not sure of that either. Also, the only report that I saw on the sample size indicates that only 18 women participated.  It’s a start, but hardly conclusive.

Finally, long-term conclusions about the capability of a person’s brain can hardly be drawn based on the results from a single test of auditory memory that is given less than two weeks after entering the world.  To see if the benefits of prenatal exercise do have any lasting effects, Dr. Ellemberg and his colleagues plan to track the infants’ cognitive, motor, and language development until they are at least 1 year old.  I look forward to seeing those published results!

While these exercise findings are both novel and encouraging, they should – as with any science – be interpreted with caution.

[Here’s a nice video from the University of Montreal’s kinesiology lab group for anyone who speaks French 🙂 or might be interested in some visual footage of the study’s methods].

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Go outside and play

Posted on November 16, 2012 | 1 comment

As the days grow shorter and colder, many of us will resign ourselves to fewer outdoor activities.  But, fighting the lethargy of winter months and getting outside may do more than just boost vitamin-D and combat seasonal affective disorder.  Moving through a natural environment has been shown to enhance attention and memory, relieve stress and depression, and boost immunity.

The therapeutic benefits of being outside may partly stem from alleviating what’s termed directed-attention fatigue, or essentially an overworked prefrontal cortex.  In a typical multi-tasking, computer-centric day, your prefrontal cortex is constantly helping you to focus attention, tune out distractions, and shift from one task to another – and back again.  A growing body of research supports the idea that spending time in nature provides some cognitive downtime and helps to restore or refresh these cognitive capacities.  This notion has led to an entire field of cognitive science known as Attention Restoration Theory (ART).

A prominent study on ART was released in 2008 by a team of scientists from the University of Michigan.  It revealed that adults performed 20 percent better on tasks of attention and working memory after a 50-minute walk in a park, compared to a walk in a noisy urban setting.  In contrast to natural environments, the authors surmise that urban environments are less cognitively restorative because they are filled with mental stimulations, many of which demand our directed attention (e.g., to avoid getting hit by a car).  A 2012 study by this same team of scientists showed similar cognitive benefits in patients with clinical depression.  Attention and memory benefited more so from the nature walk; however, mood was lifted by walking – regardless of the setting.  This is good news for those who may not have easy access to green spaces (more on exercise and depression later!).

Preliminary work by Dr. Jason Duvall (also at University of Michigan) suggests that to most benefit from exercising in nature, you really need to be present in it.  He suggests that heart-rate monitors, iPods, or GPS devices can all subtly alter the experience of being outdoors.  If you are constantly dialed in to a device and addicted to its output, you are not allowing yourself the same cognitive downtime that you would without it.

It almost seems that exercising in the great outdoors can elicits a type of meditation.  I think this is one place where endurance-type activities have an enormous advantage.  You just can’t get “lost in the moment” during a tennis match, cross-fit workout, or game of pick-up basketball.  Be it running, walking, hiking, or biking, the repetitive nature of the movements can transport you to a calm, near zen-like “zone” where you are totally caught up in the here and now.  For me, this is never more true than when I’m running through wooded trails.  It turns out; this is precisely the premise behind “mindfulness training.”  Mindfulness training essentially teaches the mind to be attentive to the present and not dwell in the past or project to the future.

Because of this link between exercise and mindfulness, a new study in the Frontiers in Human Neuroscience caught my eye this week.  Using fMRI, the authors found that 8-weeks of mindfulness training can reduce the amygdala’s response to emotional stimuli.  The amygdala is a region deep within our temporal lobes that plays a key role in processing emotions. Abnormalities here have been linked to anxiety, depression, and phobias.  So, they essentially found that by regularly engaging in mindfulness, we can provoke enduring, beneficial changes to how our brains process emotions in everyday life.  Interestingly, mindfulness training has even been shown to boost immunity by reducing pro-inflammatory gene expression.  How’s that for a mind-body connection?

The mind aside, Dr. Miyazaki and his colleagues in Japan have unearthed some fascinating physiological changes that stem from being in nature. Walking through natural environments for just 15-20 minutes can lower pulse rate, decrease blood pressure, and lower sympathetic nerve activity (responsible for the fight or flight response).  It also seems that it can physically ease stress, as concentrations of cortisol (a stress hormone) were nearly 13 percent lower after the short outdoor walk.  This group has even found benefits of forest walking on the expression of certain anti-cancer proteins and the immune system.

As winter kicks into full gear, you might reconsider hopping on the treadmill or trainer again and bundling up for a dose of nature instead.  You might even try leaving those gadgets behind.

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Armed with exercise in the fight against dementia

Posted on November 3, 2012 | 2 comments

People are always asking what they can do to protect themselves against Alzheimer’s disease and related dementias.  Concern over the risk of these ailments is evident in the tremendous success of super foods, super supplements, and mind games, all claiming to preserve mental acuity into old age.  Persuasive findings from several recent studies add to a growing body of literature suggesting that physical activity may be especially effective in the fight against dementia.

Brain imaging from a new study in Neurology revealed that seniors who are physically active have less atrophy (shrinkage) than their more sedentary peers. The integrity of their white matter was also superior, meaning that the “wiring” that connects brain regions was healthier.  These folks were in their 70s, so the grueling activities associated with these benefits were things like walking several times a week.  Interestingly, none of these same benefits were seen with mental exercises. While there may certainly be benefit to some of the mind games currently flooding the market, the promising advertising claims appear way ahead of the scientific evidence.

Just days ago, the journal Stroke published evidence that a physically active lifestyle significantly reduces the risk for cognitive impairments and vascular dementia. Vascular dementia is caused by reduced or obstructed blood flow in the brain, and limits the oxygen and nutrients reaching brain cells.  Depending on where blood flow is reduced, symptoms may include confusion, disorientation, and problems with memory or attention.  The relationship between physical activity and reduced dementia risk in this study was robust, even after accounting for education level, age, and other risk factors for dementia.

The strength of these two studies lies in their numbers (both had over 600 participants), but they are limited in that they can only demonstrate associations.  It could simply be that people with healthier brains are more likely to remain active, rather than that activity causes these benefits to the brain. Herein lies the power of intervention studies.

In a 2011 study, Erickson et al. recruited 120 older adults and randomly assigned half of them to a stretching and toning program and half to an aerobic exercise program that consisted of moderate-intensity walking of up to 40 min. at a time.  Six and 12-month follow-ups showed that aerobic exercise physically increased the size of the hippocampus.  This region shrinks in late adulthood, even in those without dementia.  This volume loss impairs memory and increases the likelihood of developing dementia. The people in this study who walked effectively reversed the age-related loss of hippocampal volume by 1 to 2 years.

I think the most powerful message here is that it is never too late.  Some of these participants started walking in their late 70s and early 80s, and their brains physically changed as a result of moving their bodies.  Never mind the reduced cholesterol and blood pressure that undoubtedly came with this exercise…regions of their brain actually grew because they were walking!  Now, there is always a need for more large-scale, controlled interventions, but the science is consistently exposing exercise as a neuroprotective factor—helping to defend against deterioration in the brain.

People are always asking what they can do to protect themselves against Alzheimer’s disease and related dementias.  It seems to me that at least one answer is pretty clear.

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Exercise: free Ritalin with no side effects

Posted on October 30, 2012 | Leave a comment

A lucrative black market now exists for the unprescribed use of stimulant drugs. It’s been in the news quite a bit lately, so I figured it an apt launching point for this blog. It appears the practice of taking ADHD medicines as “study aids” has infiltrated undergraduate student bodies and is trickling down to high schools. Some physicians have even gone so far as to prescribe these medicines “off-label” (meaning for those without any attentional disorders) to low-income children who are struggling to keep up with their peers in school. This appeared in a recent New York Times article, and the Colbert Report did a pretty great satire on the sheer lunacy of what he terms “meducation.”

I don’t want to get too caught up in the ethics or politics of this trend (I’m aware of several students and at least one friend who “supplement” with stimulants), but suffice it to say that I think it’s a slippery and dangerous slope. These drugs stimulate our central nervous systems and can have rather unpredictable effects on neurotransmitters. Some have to be placed on sleep medicines to counteract the medicine’s effects at night, and others grow depressed. There’s a reason these drugs are not available over the counter.

The thing is, who doesn’t want to be more focused and efficient with their time? What student wouldn’t love to be able to party all week and effortlessly pull off an all-nighter before acing an exam? (I’m not implying that works!) We are all busy people who’d jump at the chance to get just a little bit more done in a little less time….to be able to absorb a little bit more of what we read, to be a little more alert during that unending conference, to concentrate a little bit better on writing that report. Here’s where exercise comes in.

The feeling that you are simply a bit more “on” after a workout isn’t just in your head. errr, bad pun. Actually, that’s exactly where it is—in your head. There are very real changes that occur in response to a single bout of exercise. In this context, most people will immediately think of endorphins. Endorphins (from endogenous + morphine) are certainly released with exercise, but they have a greater impact on mood, pleasure, and pain than your ability to focus or concentrate. so, for another post!

It turns out that the systems targeted by ADD/ADHD drugs are the very same ones naturally affected by a single bout of exercise. The psychostimulants used to treat attentional disorders typically work by increasing the availability of certain neurotransmitters, most notably dopamine and norepinephrine. Likewise, a single burst of physical activity elevates the brain’s dopamine, norepinephrine, and serotonin levels. These chemicals all have an impact on our focus and attention. They serve to increase alertness and reduce our urges to seek out new mental stimulations (like that incessant pull to check Facebook just one more time). Exercise also releases epinephrine, which helps mobilize glucose (the brain’s sole source of energy), and may further enhance the availability of the neurotransmitters just mentioned.

The research (both in kids and adults) confirms these benefits of exercise on our mental performance. After exercise, subjects are able to respond more quickly and accurately to cognitive tests that challenge attention and inhibitory control. In “real life,” these lab tasks could translate to being able to tune out distractions at work or home and concentrating on getting the task at hand out of your hands. Studies that have actually measured electrical activity at the surface of the brain (using EEG) have found, again and again, that a single bout of exercise boosts markers of attentional processes. These EEG markers essentially show that more cortical resources are allocated to a given task after exercise than before, and that they’re allocated more quickly. Researchers have observed these changes in response to everything from maximal cycling bouts to a mere 20-minute stroll on the treadmill.

Increased blood flow to the brain during exercise may also explain how exercise induces these immediate cognitive benefits. More precisely, it is the nutrients (namely glucose and oxygen) carried by this blood flow that’s thought to boost our thinking. The animal research strongly supports this, but it’s much trickier to measure cerebral blood flow in response to exercise in us. I’m actually involved in a study at UMD, spearheaded by Dr. Carson Smith, that will try to do precisely that. In a nutshell, functional MRI will be used to try and compare cerebral blood flow before and after volunteers ride a stationary bike. I’ll let you know what we learn!

So, why don’t any of these stories make the news? Maybe, if exercise came in a little round pill.

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