Exercise & The Brain
Exercising has many benefits that we are used to hearing about in the media, like lowering the risk of many cancers, decreasing our chances of CHD (coronary heart disease) and stroke, halving our risk of type 2 diabetes, and many more including decreasing the onset of dementia, depression, and stress. And although I agree with all those statements, the articles in the media never really give us a proper insight / scientific description as to why exercise is good for us.
In addition to all of those aforementioned benefits, exercise also influences our ability to learn directly, at a cellular level, improving the brain’s potential to process new information.
This blog is, in part a book review, and contains some excerpts from “Spark! How exercise will improve the performance of your brain.” A fantastic book by Dr John J Ratey and Eric Hagerman. This blog takes a look at some of the neuroscience behind exercising and the brain, and explains why exercising is good for the brain. Forget fish oil and Sudoku, it’s all about exercise!
The human brain has roughly about 86 billion nerve cells or neurons. The language of the brain, so to speak, is electrochemical. Transmission is done via neurons firing and receiving electrical and chemical signals. Each nerve cell might receive input from a hundred thousand other neurons before firing its own signal. The junction between cell branches is called the synapse, synapses don’t touch, which can be a little confusing when neuroscientists talk about them “wiring together”. What actually happens is that an electrical signal shoots down the neuron (its axon to be precise) until it reaches the synapse where a neurotransmitter carries the message across the gap in chemical form. On the other side, the receiving branch of the other neuron (dendrite) has a receptor that the neurotransmitter plugs into, like a key in a lock, and this turns the signal back into electricity. If the electricity at the receiving neuron builds up beyond a certain threshold, that nerve cell fires a signal along its own axon, and the entire process repeats (information is now travelling).
About 80 percent of the signalling in the brain is carried out by two neurotransmitters: Glutamate stirs up activity to begin the signalling process, and GABA (Gamma-aminobutyric acid) slows and inhibits activity.
When glutamate delivers a signal between two neurons that haven’t spoken before, the activity primes the pump. The more often the connection is activated, the stronger the connection becomes. The saying goes, “neurons that fire together, wire together”. Which makes glutamate a crucial ingredient for learning. Glutamate is the workhorse of the transmitters but there is a group of neurotransmitters that act as regulators in the brain. Serotonin, which is often called the policeman of the brain because it helps keep the brain activity under control. It influences mood, impulse, anger, and aggressiveness. Doctors prescribe serotonin drugs like fluoxetine (Prozac) because it helps modify runaway brain activity that can lead to depression, anxiety and obsessive compulsiveness.
Norepinephrine often amplifies signals that influence attention, perception, motivation and arousal. Whereas Dopamine is thought of as the learning, reward, satisfaction, attention and movement transmitter. Methylphenidate (Ritalin) eases ADHD disorder by raising dopamine thus calming the mind.
Exercise is like taking a little bit of Prozac and a little bit of Ritalin, as it elevates, those neurotransmitters in the brain – along with all the other neurochemicals in the brain.
Whereas neurotransmitters carry out signalling, neurotrophins build and maintain cell circuitry – the infrastructure itself. The most prominent of these is BDNF (Brain Derived Neurotrophic Factor).
When the brain is called upon to take in information, the demand naturally causes activity between neurons. The more activity, the stronger the attraction becomes, and the easier it is for the signal to fire and make the connection. The strengthening between neurons is called long-term potentiation (LTP). Say you are learning a French word. The first time you hear it, nerve cells recruited for a new circuit fire a glutamate signal between each other. If you never practice or hear that word again, the attraction between the synapses diminishes, weakening the signal. You forget. Repeated activation and practice causes stronger connections to be made, and the memory physically becomes part of the brain.
This is also why it’s very important to do exercises with the right technique, as the more times you do a movement in a certain way, i.e. the more times a nerve impulse travels the same route, the stronger that pathway becomes. What starts out as a little used back road in the nervous system, with repetition, becomes a B road, then A road, dual carriage way and finally to a motorway. This adaptation is not always desirable. Once a particular way of doing something is learned, it becomes practically permanent. If an incorrect pattern or technique has been established, then this will become embedded as habit, and it is notoriously difficult to replace. The nervous system will always favour the easiest/quickest path, the motorway over the little back road – unless a lot of conscious effort is applied over a period of time.
A neuron is like a tree and instead of branches it has dendrites and at the end of the branches instead of leaves call them synapses (see diagrams earlier). More branches and synapses = stronger connections and a memory to stick.
This is where BDNF comes in. Researchers found that if they sprinkled BDNF on to neurons in a petri dish, the cells automatically sprouted new branches, producing the same structural growth required for learning information (BDNF got coined as Miracle Gro for the brain).
When Carl Cotman, director of the Institute for Brain Ageing and Dementia at the University of California, made the link between exercise and BDNF, namely that exercise elevates BDNF throughout the brain – he expected the big changes to occur in the motor sensory areas of the brain because they are involved with movement. But it didn’t, instead it showed up in the hippocampus – the area of the brain involved in memory, learning and which is extremely vulnerable to degenerative disease. This showed that exercise sparks the master molecule of the learning process, and by doing so proved there’s a direct biological connection between movement and cognitive function.
Carl’s experiment involved rodents, and unlike humans, the mice seemed to inherently enjoy physical activity, and they ran several kilometres a night. They were divided into four groups: mice running for two, four or seven nights and one control group with no running wheel set up for them. The results showed that the further the mice ran the higher the levels of BDNF in the hippocampus was seen. Looking inside their brains, the mice without BDNF lose their capacity for LTP (the strengthening of “connections” between neurons essential for learning), conversely injecting BDNF directly into the brains of rats encouraged LTP.
In 2007 a study on humans, found that people learn vocabulary words faster following exercise than when they did before exercise, and the rate of learning correlated with levels of BDNF. Along with that, people with a gene variation that robs them of BDNF are more likely to have learning deficiencies.
Cotman’s work laid the foundation for proving that exercise strengthens the cellular machinery of learning. BDNF gives the synapses the tools they need to take in information, process it, associate it, remember it, and put it into context. Which isn’t to say that going for a run will turn you into a genius! It simply means it gives you the tools required to respond to a stimulus, and make it stick!
On a final note when BDNF is unleashed a number of hormones from the body are called into action to help in the brain: IGF-1 (insulin-like growth factor), VEGF (vascular endothelial growth factor), and FGF-2 (fibroblast growth factor) to name a few.
IGF-1 is a hormone released by the muscles when they sense the need for more fuel during activity. Glucose is the major energy source for the muscles and the sole energy source for the brain, and IGF-1 works with insulin to deliver it to your cells. What’s interesting is that when IGF-1 is used in the brain it isn’t related to fuel management, but for learning – presumably so we can remember where to locate food in the environment. Which makes perfect sense in light of evolution. If we strip everything else away, the reason we need an ability to learn is to help us find, obtain and store food. We need fuel to learn, and we need learning to find a source of fuel – all these messengers from the body keep this process going and keep us adapting and surviving.
To pipe fuel to new cells we need new blood vessels – this is where VEGF comes in and builds new capillaries. Along with FGF-2 who helps tissues grow and helps to process LTP.
As we age all three of these factors and BDNF naturally trails off. However, we have some control over the situation because we now know that exercising increases BDNF, IGF-1, FGF-2, and VEGF.
The body was designed to be pushed, and in pushing our bodies we push our brains too. Learning and memory evolved in unison with movement that allowed our ancestors to track down food, so as far as our brains are concerned if we are not moving there’s no real need to learn anything. To solidify this notion, I’ll tell you about the humble sea squirt. It has a functioning brain and nervous system that it uses to swim around the ocean, until at some point during its life, it decides to implant itself onto a rock where it will remain stationary for the rest of its life. The first thing it does after implanting on the rock is to eat its own brain and nervous system as food – why?.. because it has no use for it anymore.
So the take home message is, stop being so sedentary all day Get Up and Get Active!!
Excerpts from Spark by John J Ratey & Eric Hagerman. Brilliant book explaining in detail the effect exercise has on the brain in relation to learning, stress, depression, anxiety, attention deficit, addiction, hormonal changes and ageing. Well worth a read!