After a motorcycle crash, you try to get up without success. You quickly notice your legs are no longer responding to your commands. Weeks pass and you realize that, unlike your legs, your dexterity has improved. But how did this adaptation happen?

brain plasticity

Like playdough, the brain is built according to environmental influences and can change over time. The brain is malleable. This characteristic is better known as brain plasticity.

Synaptic Plasticity

A synapse is a small space between two neurons. In fact, it is through this space that neurons send eachother messages: the neurotransmitters.

synapse brain plasticity

Synapses are made and unmade according to environmental demands. To illustrate the two processes of synaptic plasticity, I will make a comparison between synaptic connections and electrical wires.

brain plasticity

The brain is organizing itself

The brain is modulated by the environment in which we develop. So, it creates connections that will be useful in our unique context. In children, this type of brain plasticity is omnipresent, because it’s a period during which it creates a lot of connections since we are constantly learning new things. Sadly, if we lack stimulation, it will form fewer synpatic connections. As adults, we still create connections every time we learn something new. If a knowledge or skill is often required, connections will become stronger, making it easier for them to trigger.

brain pasticity
It’s as if when you’re exposed to something new in your environment, you plug a wire. So, we all get a different combination of colors depending on what we’ve learned.

The brain reorganizes itself

Also, the brain reorganizes its synaptic connections following a loss of an ability (brain injury, paralysis, etc.). For example, if we loose the use of our right arm following an accident, we stop using our motor and sensory regions associated with this part of our body. So, these motor regions no longer having specific functions can be reassigned to another role. Those neurons can convert into motor neurons controlling another part of the body, making it a little more efficent than before.

brain plasticity
When a connection is damaged in a specific region, the wire connections can be rearranged.
Taxi driver, brain plasticity

Brain Plasticity throughout Life

White and gray matter volume varies throughout life. You have probably heard both of those terms before. But do you know exactly what they’re referring to?

White matter and gray matter

The myelin sheath wraps around the axon giving it its white color. Several axons side by side form white matter. Grey matter contains the cell bodies of several neurons side by side. It includes, among other things, the neuronal nuclei.

Grey matter volume is at its peak in childhood and decreases throughout life. White matter, on the other hand, increases until 40 years old, then decreases. This means that the number of connections between different parts of the nervous system is increasing and then decreasing during life.

White matter
white matter
Higher intelligence, brain plasticity

Blindfolded

To illustrate the neural reorganization, I would like to present an interesting study showing how brain plasticity works.

Researchers wanted to know if, as in blind people, blindfolded people get their tactile perceptions increased. They separated the participants into four groups having different tasks to perform:

4 groups, brain plasticity

Some will be blindfolded at all times and/or will take braille classes for about 7 hours a day during 5 days. The blindfold used is designed to allow no light to pass through.

sensory deprivation

Effects on touch

During their stay, they are tested several times to compare their error percentage during tactile tasks. Among these tasks, they are made to do the von Frey hairs task. Nylon rods of different sizes are applied to the participant’s hand. Some are so small that they are difficult to discern. Then they had to say whether or not they perceived it.

As they performed this test several times, they noticed an increase in performance as the days went by. After 5 days, the two groups wearing the blindfold achieved a significantly higher result than the other two. When the blindfold is removed, the performance drops the next day.

Effects on the brain

The increase in performance in those wearing the blindfold still does’t allow us to conclude a brain change. It was by looking at the brain scans that they confimed that the occipital lobe, usually used to process visual informations, was activated during the tactile task.

occipital lobe

Transcranial magnetic stimulation activates parts of the brain depending on where the magnetic field is placed on the participant’s head. Stimulating the occipital lobe to reduce its effectiveness prevents it from functioning nominally. For those who wore a blindfold, the error rate is much higher than those who did not wear a blindfold when their visual areas are stimulated. It can therefore be inferred that those who are blindfolded, since they use their occipital lobe for touch, the disturbance of the lobe leads to a decrease in performance to tactile tasks. Their brains have therefore reorganized by assigning touch management to the vision region. In those who were not blindfolded, the occipital lobe was still used for vision, so the disturbance of this area didn’t affect the sense of touch.

Results

This study demonstrates the brain’s incredibly rapid adaptability even in adulthood. Until now, we don’t know whether the mechanisms of brain plasticity are exactly the same for a person who has been blind since birth as for those who are blindfolded for a few days, but the result seems similar.


In short, our brains are changing constantly. Despite the loss of grey matter, we compensate with white matter allowing us to increase the number of synaptic connections. These changes allow us to acquire new knowledge and reassign brain functions when one of them is no longer functional. With such a malleable brain, we are prepared to adapt to many contingencies.

English isn’t my first language so there might be some mistakes. If you want, let me know in the comments bellow if you found any so I can fix them. Thank you!

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Sources

Maguire, E. A., Gadian, D. G., Johnsrude, I. S., Good, C. D., Ashburner, J., Frackowiak, R. S., Frith, C. D. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences of the United States of America97(8), 4398-4403. https://doi.org/10.1073/pnas.070039597

Merabet, L. B., Hamilton, R., Schlaug, G., Swisher, J. D., Kiriakopoulos, E. T., Pitskel, N.B., Kauffman, T., Pascual-Leone, A. (2008). Rapid and reversible recruitment of early visual cortex for touch. PloS one3(8), e3046. https://doi.org/10.1371/journal.pone.0003046

Merabet, L. B., Maguire, D., Warde, A., Alterescu, K., Stickgold, R., Pascual-Leone, A. (2004). Visual hallucinations during prolonged blindfolding in sighted subjects. Journal of neuro-ophthalmology: the official journal of the North American Neuro-Ophthalmology Society24(2), 109-113. https://doi.org/10.1097/00041327-200406000-00003

Shaw, P., Greenstein, D., Lerch, J., Clasen, L., Lenroot, R., Gogtay, N., Evans, A., Rapoport, J., Giedd, J. (2006). Intellectual ability and cortical development in children and adolescents. Nature440 (7084), 676-679. https://doi.org/10.1038/nature04513

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