We’ve all cut our finger or hands, or some other part of our body, and watched over the next several days or weeks new skin cells form, grow, and thicken, a miraculous example of how the body heals itself.
For centuries, scientists have investigated questions regarding the brain’s ability to heal itself after injury or disease. Obviously, invading an individual’s skull to observe and monitor the brain after injury isn’t ethical. But the birth and growth of the neuropsychology and neuroscience fields in the 20th century, and the corresponding advances in neuroimaging technology, suddenly enabled the study of the brain in ways that had never before been possible.
While most people think of a hard, unbendable, unchangeable substance when using the term “plastic,” those in the neurosciences use the term differently. Neuroplasticity means that the brain is malleable, workable, and alterable. It signifies the ability of the brain to change, heal, and re-wire itself.
Hard-Wired vs. Plastic
The concept of a changing brain is relatively new – and a bit revolutionary. Before the 1960s, scientists considered the brain immutable or unchangeable. In other words, they believed the brain to be hard-wired by the time it was fully developed, that nothing including the environment, biochemical, or anatomical changes could alter its neuronal circuitry or structure.
Furthermore, if an area of the brain sustained an injury or damage from disease, its ability to repair wasn’t apparent, according to many scientists.
But a discovery by researchers Mark Rosenzweig, David Krech, Edward Bennett and Marian C. Diamond at the University of California, Berkeley, overturned these long-held beliefs, and began a series of startling brain studies that continue today.
These scientists compared rats caged alone, from birth to maturity, to rats caged in larger cages, with larger social groups providing more opportunity for play and interaction.
They found that the brains of rats that lived in the enriched environments had heavier brains, more connections betweens neurons called synapses, and more neurotransmitter substances. For more info, see somatosensation.
This startling discovery led other researchers to investigate the ability of the brain to grow and change based on experiential processes, and to grow and change throughout the lifespan. Other studies on mammals confirmed the scientists’ theory of enrichment altering brains, and a few studies on isolated humans have occurred as well.
In an article for New Horizons For Learning, Marian C. Diamond stated that a research study done in 1993 examined portions of the human cerebral cortex responsible for word understanding. Comparing the effects of enrichment on deceased individuals who had graduated from college to those with only a high school education, the study showed that the biopsied nerve cells in the college-educated had more dendrites than those of the high school graduates.
What are Dendrites?
Dendrites are the short branching projections that radiate from the cell’s to receive signals from other neurons, and carry those signals to the cell’s main body.
Plasticity in the Somatosensory Cortex
If the brain displays remarkable changes from living in enriching environments, how does the brain react when disease or injury affects either its anatomy or chemistry? This became a major area of scientific research after the enrichment discoveries.
In 1976, two neuroscientists, Thomas A. Woolsey, and Donald F. Wann were studying the effects of somatosensory changes in the brains of mice. (For more info, see Somatosensation)
As in human brains, the brains of mice have a cortical region of the brain that maps sensory entry points on the animal’s body, such as the snout and whiskers. The most sensitive area on a mouse for picking up sensory information is the whiskers, with each whisker forwarding sensory data to one cell cluster in the brain called a barrel. Woolsey and Wann examined the brains of mice that had whiskers removed.
If all the whiskers were removed from one side of the snout of a newborn mouse, the area of the cortex mapped to these whiskers remained silent or unused. However, if the researchers only removed a section of the whiskers, such as those in one row, the neurons in the barrels of the adjacent whiskers grew into the empty or “silent” cortex – in effect decreasing its silence.
In the 1980s and 1990s, other researchers expanded on Woolsey and Wann’s experiment using monkeys and owls, finding similar results of cortical “re-mapping” when digits are removed, or surgically fused together to form one digit where two once existed. In the case of the fused fingers, researchers found the boundaries that once existed in the cortex for each finger had essentially grown together forming a new bounded area.
Generalized to Humans
While researchers can’t remove fingers or fuse them together in humans, researchers studying individuals with syndactyly, a disorder where individuals are born with their fingers fused together, have shown similar results.
Before the individuals have their fingers surgically separated, neuroscientists take neuroimages of their brain’s somatosensory cortex, also known as the S1. Before surgery, the cortical areas reserved for each finger were noticeably close to each other and overlapped.
After surgery, there was no longer overlap. In fact, the cortical areas of S1 closely resembled those of individuals with normal hands.
Additional studies have shown that teaching blind adults Braille dramatically increases the area of S1 reserved for the single finger, usually the index finger, that Braille users employ almost exclusively. And the cortical areas of S1 reserved for the other fingers reduce accordingly.
What is the S1?
The spinal cord sends sensory information from all parts of the body to an area of the brain called the S1. The S1 is strip of cortex that runs across the top of the brain from ear to ear. What’s most amazing about this “strip” is that it contains neurons sitting there waiting for impulses from specific areas of the body. Essentially, the strip maps the entire body, from the eyes to the toes, and each body part has its own marked area on the strip. Each finger, for example, has its own space as well as each toe. After reaching the S1, the specific area processes the sensory input, sending it on to other brain areas for further processing.
In short, what all of these studies point to is the brain’s capability for an enormous amount of plasticity. And this discovery is leading researchers to investigate how this plasticity helps humans heal from brain injuries, deficits, and developmental dysfunctions.
If you find this type of brain research fascinating, you should consider a career in neuropsychology or neuroscience. Usually a Ph.D. is required to conduct this type of research, and a psychology degree is excellent preparation for both master’s and Ph.D. programs in neuropsychology or neuroscience.
Find out more about this field by requesting information from schools offering degrees in psychology.