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The Evolution of Neuroplasticity

The notion of “neuroplasticity,” that is the ability of the human brain to repair and rewire after injury or change in function, has undergone dramatic changes in the last 120 years. As early as the late 1800’s the father of modern psychology, William James, wrote extensively on the notion of neuroplasticity of the brain and quite accurately for his time. Starting in the earlier 20th century, scientist looked even closer at the brain and this notion, oddly, changed. The work of Ramon y. Cajal and others began to show structural areas of the brain that have never been described before. Further research was able to tie these newly discovered brain structures to specific functions in the human body. From this point, the 1920’s to almost the late 1990’s, the idea that the brain could significantly alter itself after injury or produce new brain cells was a lost idea. We all grew up with the idea that “You are born with a number of brain cells and then they begin dying.”


In the last twenty years amazing findings regarding the neuroplasticity of the brain have been published, including:


Taxi cab drivers after being forced to learn thousands of addresses in London, for purposes of training, developed larger areas of the brain known as the hippocampus, which is associated with memory;

The hippocampus in the olfactory areas of the brain were constantly producing new neurons though out our lives;

Children under six who undergo, unfortunately, a hemiectomy, whereby one half of their brain is taken out, are able to regain almost normal function because of the brain’s ability to rewire and literally take over the functions of the missing other half of the brain. There are limitations to this, for example, in a child who’s brain had managed to move control of a function to a new part of the brain because of the surgery, it was found that he was almost unable to learn any mathematics because the area of the brain where mathematics was learned had been occupied by another function after the surgery;

There are two types of stem cells in the human brain that can be activated for a number of reasons including injury, and can take the form and function of the missing brain matter and make repairs known as neuroregeneration. It is likely that neuroregeneration will be found to occur in all areas of the brain in the next ten years. However, it obviously does not occur at a scale where miraculous recovery from catastrophic injury can occur. Therapies and future modalities might be able to tease these cells into doing more repairs in the future.


So at the present time the brain science neuroplasticity is back in and is being talked about in thousands of studies a year. We now know that some of the plasticity, for example, in learning languages, ends at a very early age. Dr. Jeffery Schwartz in his fascinating recent book “The Mind and The Brain: Neuroplasticity and the Power of Mental Force” describes many interesting examples of neuroplasticity. It has been shown for example, that very young children of the age of two can understand and hear all of the many sounds in every language in the world. That is why language acquisition is spectacularly easy if it is done at a young age and is significantly harder as we age. Studies in Japanese adults, whereby they were asked to listen to certain English language sound, were literally unable to hear some of those sounds at all, as if they did not exists.


The young brain also responds quite adversely to lack of use. It has been shown that there is a crucial three month period in many mammals whereby if they are kept in a dark room or otherwise unable to use their eyes, that proper connections between the brain and the eye simply do not form and permanent blindness is a result. However, when there are areas in the brain that are under utilized or not utilized at all because of the lack of hearing, vision or other sensory input, that area is taken over by nearby parts of the brain and recruited to do work for them. Thus, nothing is wasted.


In a recent Wall Street Journal article, they described 2011 findings that show teenagers intellects and IQ can rise or fall as many as 20 points in just a few years. This is certainly contrary to the thinking of the last hundred years. These changes are consistent with other findings, where scientists have determined that experience can easily alter the brain and its networks of billions of neural synapses. This is consistent with some of the tenets of the relatively new concept of “Cognitive Reserve” whereby persons going through life with more active and stimulating everyday lives are more able to fend off the ravages of old age dementia and Alzheimer’s. All of these new findings but a ball squarely in each person’s court – you can alter your brain for the better and as the past President of the American Psychological Association noted “Those who are mentally active will likely benefit. The couch potatoes among us, who do not exercise themselves intellectually, will pay a price.”


While many of these findings are good news for those who have suffered brain injury, a widespread or diffuse brain injury caused by a high speed collision, for example, is currently resistant to full recovery. “Focal” or specifically located injuries are much easier for the brain to readapt and deal with. Also, unfortunately for the moderate to severely brain injured, the likelihood of becoming a couch potato because of their injury, will likely have the effect of decreasing the likelihood of positive brain restructuring through life and will result in the injured falling further and further behind their peers.


Glial Cells: The “Dark Matter” of the Brain

By the time a patient gets to the emergency room, unconscious from a trauma, the primary injury to the brain – that is the structural damage to the brain tissue, neurons and blood vessels of the brain has already occurred. However, we know that this acute injury also sets into motions a complex cascade of molecular events known to create “secondary damage” to the brain. While this very complex puzzle has not been completely unraveled, we do know that one of the chemical events that occur after trauma to the brain is “oxidative stress”. The human body generally stays in balance by producing reactive oxygen species (ROS) and using them as part of our immune system. These molecules are highly reactive and destructive and are essential for keeping our immune system intact. However, after a trauma the balance is thrown out of wack and far too many ROS molecules are thrown into the blood stream. This condition of oxidating stress is also thought to be important in many neuro-regenerative diseases such as Lou Gehrig’s disease, Parkinson, Huntington’s Disease and Alzheimers. Key structures of the brain in all of this are the glial cells, a long ignored part of our brains.


In the early 1900’s there was a battle that raged over the make-up of the human brain between brilliant Spanish scientist Raymond Cajal and Italian Camillo Golgi. Cajal proposed that brain function was a rising from neurons in the brain, which was correct, but his theory reduced another important part of the brain structure, the glial cells, to an insignificant structural role only. However, in the past fifteen years it has been discovered that the glial cells are active in the brain and involved in many parts of cognition and memory. This is exciting because the glial cells make up a huge part of the brain structure and are currently almost like the “dark matter” of the universe. They are there but no one pays attention to them and no one knows all of what they do quite yet. There are several type of glial cells present in the human nervous system:


Astrocytes- These cells outnumber neurons five to one and are also found in the brain capillaries that form the “blood/brain barrier” that restricts what substances and molecules can enter the brain. The BBB as it is called, is very important in regards to a traumatic brain injury. It is thought that one of the injuries in trauma is a tearing or weakening of the BBB. Once that occurs the destructive ROS type molecules that the BBB generally keeps away from the brain are let in. This causes inflammation and destruction of brain tissue. It is thought that epilepsy can arise from a tear in the BBB as well as alzheimers and other neuro-degenerative diseases. Every month brings more research about additional fucntions of astrocytes in the brain.

Microglia- These are small cells that remove waste from central nervous system cells and offer protection as part of the immune system.

Oligodendrocytes – These are central nervous system structures that wrap around axons (the telegraph wire long branch of a neuron) and its insulating coat known as the myelin sheath. The destruction of this material can occur in high speed accidents or blast injuries. When the axons are stretched the coating can fall off or be damaged. This disables or adversely affects the neuron because of its electrical signal is then impaired. The new technology of MR/DTI can visualize this type of injury in the white matter of the human brain very sensitively. Water molecules that are suppose to run along the inside of the myelin in a straight line are shown on MR/DTI to be moving almost randomly in all directions. This is how damage is visualized on an MR/DTI.

Schwann Cells- These cells are also involved in the myelin sheath of a neuron and assist in the conduction of impulses.

A Study published in January 2010, in Nature showed that astrocytes, which comprise 90% of all human brain cells, are indeed involved in the electrical process that constitute thinking. The astrocyte needs to give a burst of electricity during the process, and thus is intimately related with neurons and the creation of cognition, contrary to 60 years of prior wisdom.


Not until the glial system further studies will we know enough about the chemical cascade following traumatic brain injury to prevent it. Current animal studies have shown great promise as an anti-oxidative neuro-protective medicine for the compound edaravone (Wang GH, et al., 2011) which has been shown to inhibit oxidative stress and inflammatory response as well as reducing glial activation. These compounds will not be available, unfortunately, for several years.


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