21. exercise

12 01neurLecture 21; November 26, 2013Exercise

NEUR%1201%%Fall%2013%%Harry%MacKay%

Fun with Google Trends

Google searches for Exercise and Lose weight drop every December, and spike every January.

People seem to be searching less for exercise and more for lose weight every year.



Google searches for butter peak every December. Perhaps people do not understand the relationship between butter and weight gain?

Butter (and bacon) searches are on the rise



The good news is that interest appears to be declining in the superficial benefits of exercise ab exercise search frequency is declining, but brain exercise frequency is starting to increase.


Introduction There are a great many risk factors for

mental illness, and there are also a great number of factors that can exacerbate existing mental illness.

It might seem as though neuroscientists only study negative things

This is not entirely true, however. Neuroscience is beginning to catch up with psychology in its study of positive things.


Do we exercise enough? Current guidelines for daily physical activity are quite

modest 30 minutes of mild exercise per day on most days of the week is the figure usually given.

74% of adults in the US do not meet this guideline for daily moderate physical activity.

Daily physical activity has been on the decline for decades in the West.

This is presumably due to increases in sedentary office jobs, cars, computers, and so forth.

Sedentary behavior is non-sleeping idle behavior we spend most of our time sitting.

According to the US NHANES survey, people spend 58% of their waking life engaged in sedentary behavior, 39% in light physical activity (walking, etc.,) and 3% in exercise.

Sedentary behavior is an emerging risk factor for obesity, cardiovascular disease, metabolic syndrome, type-II diabetes, depression, and more.

Interestingly, increasing ones physical activity can improve many of these conditions independent of changes in body weight.


Another just-so story For most of human history, movement and

exercise was simply a normal part of everyday life. To sit idle was to starve, or get eaten by a bear.

The human body is well-adapted to physical activity. Though we are not the fastest or the strongest by any stretch, we specialize in endurance. A typical primitive hunting technique was to simply

chase an animal until it got tired and gave up. Humans would frequently pick up and move their

camps. We didnt start building permanent settlements until the invention of agriculture.

Like so many other examples in this class, the transition to modern life has removed the necessity of physical exercise. Could many of our physical and psychological

illnesses be caused, in part, but this lack of exercise?


Historical elements There has been a vague understanding of

the link between physical and mental health for millennia at least since the days of Plato.

In order for man to succeed in life, god provided him with two means, education and physical activity. Not separately, one for the soul and the other for the body but for the two together. With these two means, men can attain perfection (Plato, fourth century BC)


Historical elements It took a long time before any formal experiments or

observations were made concerning the link between physical and mental health.

In the 1930s, researchers showed that athletes had quicker reaction times than ordinary people. Back in the 1930s, the obesity epidemic did not

exist, so these findings are likely a function of physical fitness, not a lack of body fat per se.

In the 1970s, these findings were extended. Researchers showed that people who regularly played sports had faster psychomotor speed (reaction time, in other words). Importantly, this effect was only detectable in older

people. Reaction time naturally declines with old age, but exercise may protect against this effect.

The ruler drop task is a fun and easy way to measure reaction time.


Recent studies in children Aerobic fitness in children is linked to improved

performance in various cognitive capacities including: perceptual skills, intelligence, achievement, verbal ability, math ability, etc.,

This effect has been demonstrated by several large meta-analyses. The only thing that does not routinely improve with exercise is memory. This is somewhat surprising.

A study in California showed that math, reading and language performance was correlated with the time it took students to walk a mile, as well as with their BMI.

The Body Mass Index (BMI) is a rough approximation of body composition. It can be computed as: BMI = mass / height2.

The authors of this study were careful to control for common confounds, such as parental income and educational level.

Given these findings, it is ironic that physical education and recess are increasingly being cut in schools


Recent studies in children

Aerobic capacity is positively correlated with mathematics and reading achievement in school-aged children. Aerobic capacity is a measure of the maximum amount of oxygen an

individual can use during a given period of intense exercise.


Thinking critically While the aforementioned studies controlled for as

many factors as possible (parental income, etc.,), it is dicult to rule out alternative explanations.

Perhaps the dierence is in parenting? Parents who encourage kids to exercise may also

push them academically.

Or maybe the dierence is due to diet? Presumably parents who encourage healthy

lifestyles also encourage healthy eating.

Or perhaps the dierence is in neighborhood? The quality of ones neighborhood has a significant

impact on the amount of time one spends exercising. Inner-city neighborhoods make it difficult to exercise. The same goes for schools inner city schools tend to have less space for gym/exercise type activities.

What else could it be?


Studies in adults The relationship between exercise and

cognition is somewhat easier to study in adults, because cognition generally declines with age. This leaves more room for the beneficial eects of exercise.

A number of large-scale epidemiological studies have shown that physical activity is protective against Alzheimers disease. This is also true of social interaction,

intellectual engagement, and diet.

Recent data also suggests that exercise improves cognitive performance in otherwise healthy adults. Exercise thus not only protects against

dementia, but it also improves cognition in healthy people.


Specific eects on cognition

In studies where adults are made to follow an exercise program, the greatest benefits are in executive function.


Benefits of exercise on mood Exercise has well-known acute eects on

mood people typically feel better both physically and emotionally after exercising. This effect is strongest in younger adults.

The long-term eects of exercise on mood are less well-known. The most current and rigorous meta-analysis

shows a modest beneficial effect of long-term exercise on the symptoms of depression.

Out of all the studies, very few directly compare exercise and conventional treatments (antidepressants etc.,), and those that do typically find exercise to be less effective.

Even if its eects are modest, exercise has no downsides its benefits have no strings attached!


Neurobiology of exercise Neurogenesis is the birth of new neurons.

Neurogenesis is, of course, essential to the formation of the nervous system during development, but it also happens in the fully-formed adult brain. Adult neurogenesis occurs in the subventricular

zone and subgranular zone. These respectively supply the olfactory bulb and hippocampus with new neurons.

Studies in animals show that a number of conditions can influence hippocampal neurogenesis: Environmental enrichment ! Stress " Exercise ! Antidepressant treatment !

Slice of mouse hippocampus showing markers of neurogenesis.


Neurobiology of exercise If given the option, rats and mice will

happily run their hearts out on a running wheel. Rats can run as much as 5-8km in a single

night. Numerous studies have shown that this

sort of exercise increases neurogenesis in the hippocampus.

Control animal hippocampus Exercising animal hippocampus


Neurobiology of exercise In addition, exercise increases the complexity

of dendrites in the hippocampus.

This can be measured by quantifying the density of dendritic spines on the dendrites of hippocampal neurons.

Dendritic spines are post-synaptic inputs. The more spines a given neuron possesses, the richer its communication with other neurons.

Does hippocampal growth mean the same thing in rats and humans? Rats use the hippocampus extensively in

spatial navigation perhaps they are reacting to having more space to explore, and the effect is not from exercise at all.

Dendritic spines in A) Control and B) Exercising rats.


Hippocampal plasticity in humans Neurogenesis cannot be directly studied

in humans, because techniques doing so in rodents involve injecting certain chemicals and specialized post-mortem processing of brain tissue. However, neurogenesis can be inferred by

studying hippocampal volume. This is especially meaningful when

combined with a behavioral or pharmacological intervention (thereby demonstrating that hippocampal volume can be dynamically affected).

Recent studies have shown a positive correlation between hippocampal volume and aerobic capacity in elderly humans. This relationship partly accounts for the

beneficial effects of physical fitness on cognition.

Hippocampal volume in adults is positively correlated with aerobic capacity (R2=12.2). This is after controlling for other factors that also influence hippocampal volume including: age, sex, and years of education.


Hippocampal plasticity in humans

In this study, healthy volunteers and patients with schizophrenia both showed

increases in hippocampal volume after a 12 week aerobic exercise intervention.

Increase in hippocampal volume in one patient before/after exercise (an increase of 19.78%!!!)


Mechanisms Wheel-running is known to increase levels

of Brain-Derived Neurotrophic Factor (BDNF) in rats. This can explain the link between running

and neurogenesis. BDNF is also implicated in the neurogenic

action of antidepressants.

Exercise may also stimulate blood flow, as well as the growth of new blood vessels in the brain. It is difficult to tell whether this is a cause or

consequence of neural growth post-exercise.

It may depend on molecules like Vascular Endothelial Growth Factor (VEGF), as well as Insulin-like Growth Factor 1 (IGF1). Interestingly, IGF1 also acts peripherally to stimulate muscle growth.

Cerebral angiogram illustration blood supply to the brain.

Scanning electron micrograph of cerebral blood vessel ultrastructure.


What do video games do? First-person shooter (FPS) style games (Halo,

Half-Life, Call of Duty, etc.,) are associated with a number of interesting cognitive benefits.

Gamers tend to have superior multiple object tracking, spatial navigation, and better peripheral attention skills. Both of these are present in gamers, but can

also be learned by non-gamers if they are made to play FPS games.

These benefits are likely specific to the games. A recent study showed that gamers were

better than non-gamers at spatial navigation in computer simulations, but they were no better in real life.

Counter-Strike is an ancient game now, but it was always my favorite.


What about brain games? Its true that the brain works on a use it or lose it

principle, so it seems reasonable that games designed to train the brain may produce improvements in certain abilities.

Lumosity is a popular suite of brain games. Lumosity is far from the only program of its kind,

but it may be one of the more affordable ones others can cost hundreds of dollars, and may only work on computers.

Brain games like Lumosity have been studied a fair bit in patients with some form of neuropathology. Brain games do seem to have a meaningful

impact on certain elements of cognitive performance in the elderly, brain damaged, and occasionally young children with ADHD.


Do brain games work in real life? Theres no doubt that playing brain games leads to

improvements in performance on those games. The real question is whether they produce increases in

skills that transfer to other tasks.

This turns out to be dicult to study. This is partly because it is hard to decide on who to use as a control group. Studies frequently use no contact control groups, and this raises questions. No contact control groups complete the same pre-

and post-training tests, but do absolutely nothing in between. Thus it is difficult to tell whether observed effects are unique to the game being tested.

It would be better to use a placebo game.

Psychological studies generally show no or very limited generalization or transfer of skills gained during brain training games in healthy participants. More research is needed in this area, but in general the

results of well-run studies have been modest at best.


But on the bright side Wouldnt it be nice if you could run a study with millions of

participants who would volunteer all of their personal information, then spend hours a week working on tasks youve designed while their performance is recorded in precise detail? Lumosity has figured out how to do just that! Best of all, users pay for

this privilege.

Data gathered from Lumosity is now the worlds largest database of human cognitive performance. As of January 23, 2013, the Lumosity database has cognitive

performance data from over 36 million users from hundreds of countries. Practically all age, race, language, and cultural demographics are represented.

This massive supply of data makes it possible to run some very interesting analyses with a high degree of precision.


Examples:

21. exercise

Documents

necessity of physical

daily physical activity

lack of exercise

ones physical activity

brain exercise frequency

minutes of mild exercise

google trends google

sedentary behavior