Brain plasticity

Researchers of the brain have long believed that the brain, once fully grown, no longer changes. Only young brain was supposed to be plastic, as the ability to adapt is called in technical terms, and was believed to lose plasticity with time. However, research has shown that this belief is not completely correct.

Mapping monkey brains

At the beginning of the 20^th century when scientist started doing more detailed research on the distribution of different areas of the brain, responsible for the movement of individual parts of the body, they discovered it was not completely identical in all of the test animals. At first, they thought that the differences occurred due to their lack of precision, but it soon turned out that, even though the mapping of individual functions in the brain was by no means a simple task, the discrepancies were not the consequence of errors.

Researches wanted to map out the area of the brain which controls the movement of a monkey’s body, so they had to stimulate the brain part by part consecutively and write down which movement had been triggered. By stimulating a single point, for example, they triggered the movement of a finger while activating another point moved the entire hand. As brain tissue is not susceptible to pain, such mapping was not painful for the animals, but was most likely not very comfortable either.

More accurate measurements, or mappings, have confirmed that the maps of these areas of the brain were not identical in all the test monkeys. The point that triggered, for example, the movement of the hand was not located in the exact same place in all the test subjects. It turned out that the brain maps were specific to every individual monkey, much like fingerprints are specific to every individual person.

In addition, the maps revealed that the movements these animals performed together, in sequence, were controlled by neurons which were located close to one another in the brain. Scientists also discovered that the areas controlling the movements, characteristic of monkeys, occupied larger areas of the brain. If we were to illustrate this with an example from the human world, this would mean that a violinist has a substantially larger and more developed area which controls the fingers of the left hand than someone who has never played a musical instrument, an activity requiring great dexterity. Similarly, professional dancers possess a much larger area responsible for the movement of the feet than people who use their feet merely for walking.

Do brain maps change?

Of course, the question that quickly occurred was how these areas in the brain were formed and whether they could change during an individual’s lifetime. The more or less generally accepted belief of the scientists of the greater part of the 20^th century was that these areas were formed in early youth and could not undergo significant changes later. However, some skeptics decided to try and find out for themselves whether it was actually true that the map of a monkey’s brain would not change with time.

It was during time between the two world wars that researches already discovered that brain maps actually do change, most likely in proportion to the use of individual muscles. The movements executed more frequently were represented to a greater extent within the brain than the less frequent movements. However, these experiments went by relatively unnoticed because of the already established general belief that a fully grown brain could not undergo any further changes.

Despite the established belief, in the seventies, the American neurologist Michael Merzenich and his colleagues took on a more thorough research on how brain maps change under different external influences. At first, Merzenich was interested in finding out what the effect on the brain would be if a monkey would no longer receive sensory information from a specific part of the arm. He first accurately determined which areas of the monkey’s brain were responsible for processing the sensory stimuli from specific parts of the body. He then performed an operation that caused the monkey to lose feeling in one of its palms. After some time he mapped the monkey’s brain again and discovered that the area which had previously been responsible for the sensations in the thumb and its surroundings was not blank, but was now processing information from another part of the arm which still sent signals to the brain, because the nerves from that part of the arm had not been disconnected.

After this discovery he directed his research into less invasive procedures. He was curious whether the brain maps would also change if he taught the monkeys a new skill. He and his colleagues conducted a rather elaborate experiment in which they taught adult monkeys to use their fingers with great precision. The monkeys would get their reward only if they used the correct amount of pressure while handling a device. For them this was by no means a simple task, because they had to invest a lot of effort into training their fingers in order to get to the reward. It was no surprise that at the same time the researchers also discovered that the area in the monkey’s brain which controlled the movement of the fingers grew substantially with use.

How can the blind read?

The same characteristics that had been discovered in monkeys were later confirmed in people as well. There was an interesting research which focused on how the brains of blind people could process Braille. Scientists first found out that the area of the brain which processes the sensations in the reading finger of a blind person grows, which came as no surprise. What was more fascinating, though, was that the area responsible grows at the expense of the surrounding area, which the brain attributes to the remaining fingers. In a person who becomes skilled in reading with a finger, the area for processing the sensations in the principal reading finger grows, but does so at the expense of diminished space attributed to the remaining fingers.

Researchers stumbled on an even greater surprise when, using more modern methods, they discovered that during sleep, even in blind people, the area which is otherwise responsible for processing visual signals becomes active. This area was not expected to be active in blind people, as they do not receive any signals from their eyes, leaving this area in a passive state.

Nonetheless, it seems the brain is so adaptable or, in other terms, plastic, that an area not being used adjusts and becomes specialized in other tasks. In the mid-nineties, however, this discovery would not be easily accepted. The scientist that detected this particularity while observing the brain activity of blind people reading Braille encountered great difficulties when they tried to publish their findings. Science magazine refused to publish their work, because the editorial staff could not come to terms with how completely different parts of the brain could interconnect and work together, performing new tasks. In time, the article was published in the rival Nature magazine.

Later, new research actually revealed that the cooperation of the visual part of the brain has an essential role in the fluent reading of Braille. Someone who can read Braille fluently does not feel the dots on the paper at all, but directly perceives entire words, just as one reading ordinary writing is not conscious of individual letters, but takes in words and sentences as units of meaning.

In 2000, there was even a case, described in scientific literature, of a woman who has been blind since her early childhood and had learned to read Braille very well during her schooling. When she was 26, though, she suffered from a brain stroke in the area otherwise responsible for processing visual information. At first glance, such a stroke should not leave any significant consequences on a blind person, but this case seemed to prove otherwise. Even though the woman could still feel the dots of Braille under her fingers, she suddenly no longer understood their meaning. Her ability to read Braille was stored in the area that otherwise processes visual information, but in her case that had been damaged by the brain stroke.

Mental fitness

It has only recently become clear that even older brain is much more plastic or adaptable than it was first presumed to be. Nevertheless, the fact remains that the ability to adapt diminishes with time. Younger brains are simply much more plastic than older brains.

Michael Merzenich, one of the already mentioned pioneers in the research of brain plasticity, and his colleagues have already founded two companies offering professional help in overcoming difficulties in brain function. Scientific Learning helps children with learning disabilities. Using special computer games which are designed to develop specific parts of the brain that cause these children to have problems, the company has achieved impressive results.

These results have recently led to the creation of the Posit Science company which focuses on helping the older population. Using various mental fitness techniques it helps older people keep their brains in the same shape as they were in their best years.