2.6 The Amazing Brain

Brain Games Christina’s dramatic recovery was facilitated by physical, occupational, vision, and speech therapy. “The more therapy,” says Christina, “the better chance of recovery.”

William Johnson

When Christina was wheeled out of surgery, her mother approached, grabbed hold of her right hand, and asked her to squeeze. Christina squeezed, demonstrating that she could understand and respond to language. Remember, she still had her left hemisphere.

Christina may not have lost her language abilities, but losing the right hemisphere did come at a cost. We know that Christina suffers partial paralysis on the left side of her body; this makes sense, because the right hemisphere controls movement and sensation on the left. We also know that it took Christina extra time to do her schoolwork. But if you ask Christina whether she has significant difficulty with any of the “right-brain” tasks described earlier, her answer will be no.

Christina’s recovery has been nothing short of astonishing. After the surgery, she went back to school and outperformed many of her classmates. In addition to making the honor roll and leading the bowling team, she managed to get her driver’s license (even though some of her doctors said she never would), graduate from high school, and go to college. These accomplishments are the result of Christina’s steadfast determination, but also a testament to the brain’s amazing ability to heal and regenerate.

Neuroplasticity

The brain undergoes constant alteration in response to experiences and is capable of some degree of physical adaptation and repair. Its ability to heal, grow new connections, and make do with what is available is a characteristic we refer to as neuroplasticity. New connections are constantly forming between neurons, and unused ones are fading away. Vast networks of neurons have the ability to reorganize in order to adapt to the environment and an organism’s ever-changing needs, a quality particularly evident in the young. After brain injuries, younger children have better outcomes than do adults; their brains show more plasticity (Johnston, 2009).

In one study, researchers removed the eyes of newborn opossums and found that brain tissues normally destined to become visual processing centers took a developmental turn. Instead, they became areas that specialize in processing other types of sensory stimuli, such as sounds and touch (Karlen, Kahn, & Krubitzer, 2006). The same appears to happen in humans. Brain scans reveal that when visually impaired individuals learn to read Braille early in life, a region of the brain that normally specializes in handling visual information becomes activated, suggesting it is used instead for processing touch sensations (Burton, 2003; Liu et al., 2007).

Cure All? Because stem cells can differentiate into any type of cell in the body, they have great therapeutic potential. The cells pictured here are derived from a human embryo, but stem cells also reside in various adult tissues such as the brain and bone marrow.

Professor Miodrag Stojkovic/Science Source

Remarkably, this plasticity is evident even with the loss of an entire hemisphere. Researchers report that the younger the patient is when she has a hemispherectomy, the better her chances are for recovery. In fact, even with the loss of an entire left hemisphere (the primary location for language processing), speech is less severely impacted (though some impact is inevitable) in young patients. The younger the person undergoing the procedure, the less disability is evident in speech (Choi, 2008).

Scientists once thought that people were born with all the neurons they would ever have. Brain cells might die, but no new ones would crop up to replace them. Thanks to research beginning in the 1990s, that dismal notion has been turned on its head. In the last few decades, studies with animals and humans have shown that some areas of the brain are constantly generating new neurons, a process known as neurogenesis, which might be tied to learning and creating new memories (Eriksson et al., 1998; Gould, Beylin, Tanapat, Reeves, & Shors, 1999; Reynolds & Weiss, 1992).

Baby Beethoven For millions of Chinese children, learning to play an instrument like the violin or piano begins early. Children with musical training outperform their untrained peers on tests of IQ and language skills. Is this because music lessons make children smarter, or because smart children are more likely to take them? Researchers are still trying to get to the bottom of this conundrum.

Lou Linwei/Sinopix

The cells responsible for churning out these new neurons are known as stem cells, and they are quite a hot topic in biomedical research. Scientists hope to harness these little cell factories to repair tissue that has been damaged or destroyed. Imagine that you could use stem cells to bring back all the neurons that Brandon lost from his injury or replace those that Christina lost to surgery. Cultivating new brain tissue is just one potential application of stem cell science. These cellular cure-alls might also be used to alleviate the symptoms of Parkinson’s disease, or replenish neurons of the spine, enabling people with spinal cord injuries to regain movement. Both have already been accomplished in mice (Keirstead et al., 2005; Wernig et al., 2008). Although embryonic stem cells can be used for such purposes, some stem cells can be found in tissues of the adult body, such as the brain and bone marrow.

Earlier we explained how neuroplasticity is more evident in young people. So what can we do to promote positive brain changes in our children? Some people think that early exposure to music is a critical factor, but is there evidence to support this belief?

From Bumps to Brain Scans: We’ve Come a Long Way

Both Brandon and Christina underwent many brain scans before and after their surgeries, which allowed doctors to get a detailed look inside their heads without lifting a scalpel. But had Brandon and Christina lived in a different era, brain scans would not have been an option.

Before there were technologies to study the brain, people could only speculate about what was going on beneath the skull of a living person. One theory was that bumps on a person’s skull could reveal characteristics about him. Judging the topography of a person’s head was a core part of phrenology, the now discredited brain “science” that achieved enormous popularity at the beginning of the 19th century through its founder Franz Joseph Gall (1757–1828). But flaws in the theory behind phrenology were recognized early on. Another early (but more scientific) way of studying the brain was through ablation, a technique used by physiologist Pierre Flourens (1794–1867) to determine the functions of different brain regions (Pearce, 2009). This technique involved destroying parts of the brain of living animals and then determining whether some functioning was lost following this surgery.

All in Your Head Are you a secretive person? How high is your self-esteem? The answers to these questions lie on the surface of the skull, or so claimed 19th-century phrenologists, such as the one depicted in this 1886 illustration (left). The phrenological map (right) shows the locations of brain “organs” thought to be responsible for various psychological traits.

left: ©North Wind Picture Archives/The Image Works; right: Image Asset Management Ltd./SuperStock

These days, scientists no longer try to interpret what’s going on inside living brains by running fingers over people’s heads. There are now technologies that allow us to sift through the brain’s constant buzz of activity, behold its three-dimensional structure, and identify interesting hot spots (TABLE 2.1). Nevertheless, one of Gall and Flourens’ major contributions was the idea that there might be areas of the brain that have particular functions. In other words, there are locations in the brain that are responsible for specific brain activities: there is a localization of function.

In the past, most of what scientists learned about the brain came from probing the skulls of cadavers and observing the behavior of people suffering from brain damage. But the last century, and particularly the last few decades, has witnessed an explosion of brain research technologies. Such technological advances have made it possible to observe the brain as it makes decisions, sleeps, and even tells lies (Dang-Vu et al., 2008; Hampton & O’Doherty, 2007; Kozel et al., 2009). See TABLE 2.1 for information on the different types of technologies, their function, uses, and limitations (also see Infographic 2.3). With the technology available today, we can even track the activities of strings of neurons.

INFOGRAPHIC 2.3: Ways to Study the Living Brain

For hundreds of years, scientists interested in the brain were limited to surgical techniques, often on cadavers. Imaging and recording technologies now allow us to investigate the living brain by assessing structure, function, or both. CAT and MRI techniques provide static pictures of brain structures, while functional imaging and recording techniques allow us to see the relationship between brain activity and specific mental functions. Functional techniques can also be used to diagnose injuries and diseases earlier than techniques that look at structure.

New technologies are continually being developed, allowing us to study the brain in ways we couldn’t imagine just a few years ago.

Credits: Cat Scan, Southern Illinois University/Science Source; EEG, Science Source; MRI, Living Art Enterprises, LLC/Science Source; Person in MRI, Science Source; PET Scan, National Institute on Aging/Science Source; Syringe, Thinkstock; Horizontal cross-section of brain, Laboratory of Neuro Imaging at UCLA and Martinos Center for Biomedical Imaging at MGH, Consortium of the Human Connectome Project