Update: I learned only recently that some of the information in this article is outdated, and that plasticity is not what it immediately appeared to be. It is still something awesome, but some experiments have showed that it is not as powerful as it initially seemed. You can read about one of these in Karn Stromswold’s article found here. Original article follows ->

The brain is wider than the sky,
For, put them side by side,
The one the other will include
With ease, and you beside.

The brain is deeper than the sea,
For, hold them, blue to blue,
The one the other will absorb,
As sponges, buckets do.

The brain is just the weight of God,
For, lift them, pound for pound,
And they will differ, if they do,
As syllable from sound.
~ Emily Dickinson

For centuries we have tried to search for a homonculus within us, that center within our brains that makes us human. Traditionally, we expect this part to transcend all chemicals, and fall in the realm of infinite.

What makes us human? Several factors interacting in complex ways. But if there was one that played the primary role in making us “us”, it would be ‘Neuroplasticity’.

Plasticity allows our brain to break and reconstruct neural pathways. As we go through different experiences and learn new things, new synaptic connections are formed at the expense of old, unused ones. This process is not just limited to the memory organs of the brain, but even the functional ones. For example, if your visual cortex does not do any “learning” or is not exposed to the correct type of information during a critical period, your anatomically perfect eyes may never develop vision. Most likely in this case, your visual cortex which has so far gone unused would break with it’s quasi-predetermined circuitry, and reform to be used by a neighboring part of the brain.

Perhaps more amazingly, in recent decades, the brain has also been observed making recoveries after structural damage. People who suffer from any kind of mental injuries were thought to have completely and permanently lost those abilities. But with the help of MRIs and CAT-scans, researchers noticed that the injured or dead part of the brain can come back to life. It is a tragedy that this information is not yet widespread. Stroke patients who are left paralyzed or are unable to speak after their accident often never try to repeat those lost activities. However, recent cases have shown that often the “broken” part of their brain can recover in full, but since the activity previously assigned to it is no longer performed, it gives up it’s original function and becomes involved in something else.

People who undergo hemispherectomies can make amazing recoveries if their new minds are given the right exercises. It was until the early 1990s considered that the left hemisphere, primarily Broca’s and Wernicke’s areas were solely and exclusively responsible for language. The theory seemed shaky from day one. Not only could we not explain how these functioned (as we can’t yet), but perhaps more importantly, we were unable to recreate any disorders that seemed to emerge from them. But when patients left with only the right hemisphere of their brains defied current theory and produced from single worded to multi-phrased cogent sentences, the theory was just as well out the door.

It is now understood that this ability stays with us for our lifetimes. There are a few known critical periods during which specific functions are favoured. As babies, our mind’s first priority is to develop the key abilities  we use to navigate the world. After the age of two and a half or three, our brain devotes great attention to language learning, as well to sharpening the previously learned skills. After about six, we learn a tremendous amount of things about the world around us…how and why our parents behave, why the sky is blue, and in general how the world works. After about 10 – 12 we turn our attention to sexual maturity and of course the social concerns that come with it.

From this point on, the two sexes begin to differ. But now these changes are very relative, and hardly as crucial. The mind has fully developed, and the rest are the stages of our lives. Missing even one of these critical steps can tremendously change our lives. I personally know of no case where postponing something like language learning has eventually led to “normal” efficacy of that skill, and I can’t imagine it would ever happen. But again, as stated above, some recovery is still possible. It has been observed though that as we get older, neurogenesis occurs in fewer and fewer parts of the brain, being eventually left only in the hippocampus (short-term memory functions). So it is possible to understand why we eventually pass away.

Some recent experiments demonstrate the extreme ways is which our brain can change if subject to abnormal stimulus. One group of researchers cross-connected the audial and visual cortexes of the brain of a Ferret fetus. The experiment’s purpose was to test the permanence of these structures. The experiment’s hypothesis was that they are both very plastic. Indeed this was found to be the case. Visual signal being carried from the retina to the audial cortex produced very similar patterns to what the visual cortex of a normal Ferret would later produce. This implied that the modified audial cortex was now capable of “seeing” and the modified visual cortex was now capable of “hearing”.

One comfort I take from these flurry of discoveries is that they fit in perfectly and beautifully with the modern evolutionary theory. It is very difficult to explain how the brain got to be so complex if all parts evolved by individual selection. But if we understand that these parts are developed as much from their enviornment as from their genes, we see a much more reasonable and explicable world. Understanding neuroplasticity has opened a whole new field of medical care, and has revolutionzed the world of so many. Some have also found applications of it in the so-called Brain-Computer Interface technolgy. But perhaps the greatest reward this discovery holds for us is the secret of how the brain actually works.