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One Neuron at a Time

By Tim Walsh | Final Research Essays

The human mind is the most complex entity that exists in the known universe.  The mind is defined as a collection of neurons, or nerve cells, that continuously receive input from the outside world, process that information, and then send it to other neurons in order to give rise to the conscious and unconscious states experienced everyday by humans all around the planet.  There are roughly 100 billion neurons, making tens of thousands of connections every second (Schwartz and Begley 105). Due to our still primitive understanding of the mind, many believe in the solely left- brain individual and right-brain individual.  Furthermore, others are convinced that the neuronal connections in the brain are fixed and can never be changed. Still, more people assume that the brain and thought are completely separate.  They think that the outside world must always influence what goes on inside the mind.  However, thousands and thousands of neuronal connections in the mind are influenced every single day by thought. The age-old adage “mind over matter” undoubtedly got it right; thought, along with experience, physically changes the structure and function of our brains. Neuroplasticity, as this concept is known, allows for billions to change their inner world everyday, making possible a life that would be otherwise inconceivable if it were not for the incredibly “plastic” brain.[1]

Many believe that the left and right sides of the brain are completely separate entities, meaning that they do not “communicate” or influence one another. According to this theory, the brain is hard-wired for specific areas to perform specific functions. This is not the case.  Different parts of the brain influence one another all of the time causing innumerable “plastic” changes of the mind. As psychoanalyst Norman Doidge says, the right is normally the “artistic” and “imaginative” brain that controls spatial recognition, while the left is “the verbal domain” (260).  However, lateralization in the brain allows for these to interact and to physically change the neuronal connections in the brain.[2]

The experiments done by Roger Sperry on severed corpus callosa epileptic patients in the 1960s show the importance of communication between the left and right sides of the brain.[3]  In extreme cases of epilepsy, the patient’s corpus callosum is surgically severed in order to prevent the spread of a seizure from one hemisphere of the brain to another (Gibb 89).  In the experiments, Sperry flashed a picture of an object, such as a fork, into the left visual field of the patient, so that it would be processed in the right side of the brain.  He then asked the patient what he saw, but the answer was difficult to formulate since the language processes are in the left side of the brain (Gibb 90).  The right hemisphere is unable to communicate with the left, so the patient cannot name the object. In some cases, the patient made up a word such as “spanner” in order to compensate (Gibb 90).  Roger Sperry’s experiments show that the left depends on the right, and vice versa, meaning the two are indeed connected. Undoubtedly, the left and right hemispheres of the brain are a single communicating unit influencing one another all of the time.  Despite the evident interactivity displayed, the severed corpus callosa patients do not display the power that the left and right sides of the brain have in making “plastic” changes.

The story of a girl born with only half of a brain illustrates how neuroplasticity makes some lives possible and all lives better. Michelle’s tale begins inside the womb when complications caused her to be born with only the right half of her brain (Doidge 258). Despite only having half of a brain, Michelle is able to pray, read, watch movies, and love -functions of both the left and right brain- all thanks to the fact that her right-brain took over the functions of her left-brain (Doidge 259).  She is able to read, comprehend, and discuss important issues even though she has no left hemisphere, which is said to be the verbal area of the brain.  As psychoanalyst Norman Doidge says, “it’s hard to imagine a better illustration or indeed a greater test of human neuroplasticity” (Doidge 259). The right side of Michelle’s brain had to take over the functions of the left side and also had to economize its “own” functions (Doidge 259). This shows further the great power of neuroplasticity, since the right side of the brain adapted, changed, and evolved language and spatial functions without any input from the left side of the brain.  Michelle’s story confirms that the brain is not hard wired for specific areas to perform specific functions; she can perform functions of both hemispheres with only half of her brain. Although Michelle is very capable, she does have some physical and processing limitations, which seem to suggest that neuroplastic changes are not taking place. In fact, the exact opposite is true.

Her disfigured wrist, which is bent and twisted, shows signs of a missing hemisphere. Michelle has trouble seeing objects in her right visual field since she lacks the left side of the brain that would normally process this visual input (Doidge 261). On the surface, it seems that Michelle’s brain has failed to make the plastic changes necessary for her to process visual input in her right visual field; but, when examined more closely, one can easily see the fantastic neuroplastic changes her brain has made. Due to her lacking vision, Michelle has hypersensitive hearing that allows her to hear what she cannot see, such as her brothers attempting to steal her French fries (Doidge 261).  Michelle’s area for hearing on her brain map has actually partially taken over the area for processing vision, causing hypersensitive hearing.[4] The neurons for sight physically changed their structure and function in order to process auditory input, showing another sign of the brain’s ability to adjust.  The fact that Michelle lacks some functions does not show that the brain is rigid, as some would quickly assume. Instead, it shows the amazing adaptability of the human brain. Michelle’s life was enhanced by the ability of her brain to respond to and change with environmental stimuli.

The examination of phantom limb patients further confirms that neuroplasticity improves lives by enabling the brain to change in response to receiving sensory input from the outside world. The inputs received from the outside world rewire the brain more concretely because specific neurons in the brain are connected to the neurons that take in the senses all over the body. Neurologist V. S. Ramachandran describes a phantom limb as “an arm or leg that lingers indefinitely in the minds of patients long after it has been lost in an accident or removed by a surgeon”(22). Simply put, the sensation of the limb is still felt by the patient even after losing the limb.  When body parts distinct from the lost limb are stimulated, the sensation is also felt in the phantom limb, revealing the nature of neuroplasticity.  A certain area of the brain receives certain specific sensory input.  For example, there is an area for the genitals, which lies next to the area for the feet, which lies next to the space for the trunk (Ramanchandran and Blakeslee 26).   This cortical representation is known as a brain map.[5] When someone loses a limb, the brain map will reorganize, meaning that the neurons for the genitals will take over the area for the feet and cause sensation to the genitals to be felt in the feet, even though the feet are not physically present (Ramachandran and Blakeslee 36).  Ramachandran believes that when a part of the body is lost “its surviving brain map hungers for incoming stimulation and releases nerve growth factors that invite neurons from nearby maps to send little sprouts to them” (Doidge 183). This process culminates in the existence of a phantom limb and shows empirical evidence that sensory input influences the physical connections made by neurons, further supporting neuroplasticity.

But how is neuroplasticity helping the affected phantom limb patients? World-renowned psychologist Oliver Sacks says that many patients with phantom limbs experience persistent phantom pain (Sacks, The Man Who 69).  Furthermore, Dr. Herta Flor of Humboldt-University in Berlin, Germany and her team found that there is a direct positive correlation between the amount of pain experience by phantom limb patients and the amount of cortical reorganization (Flor et. al 482). Simply put, the more changes the neurons made, the more pain the patients experienced. It might seem as though neuroplasticity is causing only pain and discomfort to the patient. However, when one investigates the procedure to get rid of phantom limbs, neuroplasticity shows how it immensely improves the lives of the phantom limb patients.

Many phantom limb patients have phantoms that they experience as paralyzed, immovable.  Ramachandran attributes this to the fact that many amputees had their limbs in casts or slings for an extended period of time prior to amputation, which caused the brain to believe that the limb was frozen because it never received feedback that the limb was moving (Doidge 185). Thus, the brain reorganized its motor neurons, convincing itself that the limb was paralyzed.  Then, once the limb is amputated, the brain still believes that the limb is immobile. Since the brain is certainly not receiving any input to tell it otherwise, a paralyzed phantom limb results (Doidge 185). The good news is that the brain is malleable enough to reverse this situation through a simple therapy technique developed by Ramachandran.  He designed a mirror box that fools the brain into believing that the patient still has both arms, even if one has been amputated.  The patient inserts their good arm into the box, and they can actually “see” their phantom move, as well as feel it move (Doidge 186). Over several weeks, the patient uses the box to fool the brain into thinking they are moving their phantom limb, without even having an arm to move.  The paralysis is unlearned by stimulating a plastic change, which would rewire the brain map (Doidge 187). The first patient of Ramachandran to use this device, Philip, was thrown from a motorcycle a decade before, damaging the nerves in his arm and causing him to have an immovable, yet present arm (Doidge 187).  He eventually opted to have his arm surgically removed, but he was left with a “frozen” phantom limb (Doidge 187). After four weeks of using the mirror box, Philip’s phantom not only became permanently unfrozen, but actually disappeared (Doidge 187).  The amazing neuroplastic brain had, yet again, improved the life for another unfortunate person. 

Stroke patients are another group helped by the neuroplastic brain. A stroke occurs when a blood vessel going to the brain is either blocked or is ruptured causing blood flow to that particular area of the brain to stop, which, in effect, kills those brain cells (Stroke page #?).  These dead brain cells often times cause paralysis in the body part that corresponds to the area of the brain where the dead cells are located.  In the early 1990s, behavioral neuroscientist Edward Taub began to work with stroke patients in order to try and restore some movement to their paralyzed limbs (Schwartz and Begley 187).  He did so by using a technique called constraint-induced movement (CI) therapy, which included the patients restraining their working arm and only being able to use their impaired limb (Taub 347).  He began with patients who were in the top quartile of stroke patients in their ability to move their affected limbs, meaning they were able to “extend their wrist a minimum of twenty degrees and to flex each finger a minimum of ten degrees” (Schwartz and Begley 189). Two weeks after therapy, the patients had regained considerable use of their seemingly paralyzed limbs (Wolf et. al 2104). More importantly though, the patients could complete daily-tasks 97% more effectively after just one month of training (Schwartz and Begley 191). Taub went on to study patients in the second and third quartiles, patients with more restricted use of their affected limbs as well. He found that CI therapy worked for them but not nearly as well as for those who began with higher functioning limbs (Schwartz and Begley 192).

So, what is the origin of this improvement? If neuroplastic changes were taking place, then one should be able to empirically measure those changes. It is not enough just to see the people moving their limbs to conclude that neurons are physically changing their structure or that brain maps are reorganizing. Most importantly,one must see the changes in the neurons to say that neuroplasticity is acting,especially when considering the fact that the patients in the second and third quartiles did not improve as much as those in the first quartile,

In 1998, the first visual evidence of neuronal changes appeared in a study by Joachim Liepert and Cornelius Weiller of Friedrich-Schiller University in Jena, Germany (Scwhartz and Begley 192).  They evaluated six chronic stroke patients, who had undergone the constraint-induced movement therapy, before and after they received Taub’s treatment (Liepert and Hamzei 710-711).  All six patients improved in motor function (Schwartz and Begley 192). But, more importantly, “following CI therapy, the formerly shrunken cortical representation of the affected limb was reversed” and “an increase of excitability of the neuronal networks in the damaged hemispheres” was found (Schwartz and Begley 192-193).  An expansion of the brain maps of the affected limbs was seen using brain-imaging techniques. Also, an increase in electrical activity was shown in the damaged brain areas, which corresponded to the damaged limbs. Furthermore, the physical changes in neuronal connections thought to be occurring during CI therapy were actually seen for the first time, therefore proving that neuroplasticity altered the brain.  To further understand how neuroplasticity can save people, as it did for the stroke patients, one must investigate “mental force” and its use in helping the obsessive compulsive.

Mental force is the willful, effortful use of one’s thoughts used to amend the neuronal circuits in the brain.  Neurologist Jefferey M. Schwartz, who coined the term, was able to harness this mental force in order to create a four-step method to treat Obsessive-Compulsive Disorder (OCD).  OCD is an anxiety disorder that is characterized by recurrent, unwanted thoughts, known as obsessions, and repetitive behaviors, referred to as compulsions (NIMH). In the brain of someone afflicted with OCD, there are two neuronal pathways that can be taken: one that leads to a compulsion or obsession, and one that leads to a behavior that takes the person away from the obsession or compulsion.  Dr. Schwartz created a process with four steps: relabel, reattribute, refocus, and revalue in order to improve the lives of those with OCD.

The Four-Step Method, as he called it, would change the brain, making it easier for the afflicted patient to follow the neuronal pathway to behavior that was not obsessive or compulsive (Schwartz and Begley 87).  Relabeling is when patients recognize that the “obsessive thoughts and compulsive urges…are inherently false and misleading” (Schwartz and Begley 80). The afflicted “relabel” the thoughts and urges as a mere confabulation of the mind, a symptom of OCD.  The next step in Schwartz’s theory, “reattribution,” argues that these obsessions are due to faulty brain wiring, and the obsession is not the actual “self” (Schwartz and Begley 81).  The third step, refocusing, is the most important one because it lays down the circuit for non-obsessive, non-compulsive behavior.  When the patient feels the need to act on an urge, they focus their attention on something that is not compulsive.  For instance, if someone has the urge to constantly wash his hands, he will focus his attention on gardening, rather than act on the urge (Schwartz and Begley 83).  Every time a compulsion arises the person must refocus his attention away from it, and over time this becomes easier and easier until the “good” pathway is followed every time.  This shows the great impact of neuroplasticity since the neuronal pathways are actually changed.  The person goes from following the diseased pathway to following the healthy one. Revalue, the final step, “means quickly recognizing the disturbing thoughts as senseless, as false, as errant brain signals not even worth the gray matter they rode in on, let alone acting on” (Schwartz and Begley 88). The afflicted must step outside of themselves and see their thoughts as nothing more than the disease.  The Four-Step method developed by Dr. Schwartz shows how thought leads to neuroplastic changes in the brain to help improve the life of someone with OCD.

The immense power of neuroplasticity improves the lives of billions everyday.  By understanding that the two halves of the brain are constantly communicating, one can more easily see the enormous changes that take place inside the brain of someone who only has half of a brain, such as Michelle.  Although Michelle’s case is a rare one, there are many more people with phantom limbs who also experience the power of the brain to change its neuronal connections, which leads to a more normal and pain-free life.  Still more are debilitated annually by stroke, but the brain is there to assist again by reorganizing its maps in order to regain use of formally paralyzed limbs.  Finally, there are those who are inundated with obsessive and compulsive thoughts who must use mental force to change the plastic brain, so their lives are certainly more enjoyable.  In a world without a plastic brain, none of these amazing stories of recovery would be imaginable. However, one does not need to experience a stroke to see the neuroplastic brain in action. Someone might just be experiencing depressive thoughts, and all that she needs to do is change her thought pattern in order to change the neuronal connections to follow the “good” pathway.  Neuroplasticity is not all about miraculous stories of recovery from debilitating diseases.  It is simply that every individual has, inside himself or herself, the ability to change their own individual world, one neuron at a time.

[1] Plastic means that the brain contains “changeable, malleable, [and] modifiable” aspects (Doidge xix).
[2] Lateralization shows that the brain exists as two hemispheres, the left and right, that act separately, yet still interact with one another.
[3] The corpus callosum is a thick, flat bundle of nerve fibers that connects the two hemispheres of the brain (Gibb 89).
[4] A brain map refers to the idea that a certain area of the brain receives certain specific sensory input.
[5] Cortical deals with the cerebral cortex of the brain, which is the wrinkled part that resembles a walnut.  It is split into four areas: parietal, temporal, orbital, and frontal.



Doidge, Norman. The Brain that Changes Itself. New York: Penguin Books, 2007.

Flor, H., T. Elbert, S. Knecht, and C. Wienbruch. "Phantom-limb pain as a perceptual correlate of cortical reorganization following arm amputation." Nature 6531 (1995): 482.

Gibb, Barry J. The Rough Guide to The Brain. New York: Rough Guides Ltd., 2007.

Levitin, Daniel J. This is Your Brain on Music: The Science of Human Obsession. New York: Penguin Group, 2006.

Liepert, Joachim, and Farid Hamzei. "Two different reorganization patterns after rehabilitative therapy: An exploratory study with fMRI and TMS." Neuroimage 31.2 (2009): 710-20.

Melzack, Ronald. "Phantom Limbs." Scientific American 276 (1997): 84-91.

“Obsessive Compulsive Disorder.” National Institute of Mental Health. 17 Sept. 2009. 19 Sept. 2009. <>.

Ramachandran, V. S. "Phantom limbs, neglect syndromes, repressed memories, and Freudian psychology." International Review of Neurobiology 37 (1994): 369-72.

Ramachandran, V. S., and Diane Rogers-Ramachandran. "Synaesthesia in phantom limbs induced with mirrors." Proceedings, Biological Sciences 263 (1996): 377 86. Print.

Ramachandran, V. S., and Diane Rogers-Ramachandran. "Touching the phantom  limb."  Nature 337 (1995): 489-90.

Ramachandran, V.S., and Sandra Blakeslee. Phantoms in the Brain: Probing the Mysteries of the Human Mind. New York: HarperCollins Publishers, 1998.

Sacks, Oliver. An Anthropologist on Mars: Seven Paradoxical Tales. New York: Random House, 1995.

- - -, A Leg to Stand On. New York: Harper and Row, 1984.

- - -. The Man Who Mistook His Wife for a Hat. New York: Simon and Schuster, 1998.

Schwartz, Jeffrey M., and Sharon Begley. The Mind and the Brain: Neuroplasticity and the Power of Mental Force. New York: HarperCollins Publishers, 2003.

Taub, Edward. "Technique to improve chronic motor deficit after stroke." Archives of physical medicine and rehabilitation 74.4 (1993): 347-54.

“The Split Brain Experiments.” Nobel Prize. 30 October 2003. 18 October 2009 <>

Pietsch, Paul. “Splitting the Human Brain.” Indiana University. 18 October 2009 <>

Wolf, Steven L., Carol J. Winstein, J. P. Miller, and Edward Taub. "Effect of Constraint Induced Movement Therapy on Upper Extremity Function 3 to 9 Months After Stroke: The EXCITE Randomized Clinical Trial." American Medical Association 296.17 (2006): 2095-104.

“What is Stroke?” National Stroke Association. 2009. 18 October 2009. <>