Modern sports are unique human activities. They involve strenuous, repetitive physical and psychologic training assisted by modern equipment. Professional athletes (and some amateurs) are always preparing for competition. In many cases, modern sports training is pushing human systems to their physiologic limits. Thus, because of the intimate brain-body interaction, understanding the brain in sports is of utmost importance. It is a two-way process in that the behavior of the athlete modifies the brain and the brain modifies behavior.
There is also interaction between genetic makeup and behavior. Most people assume that genes shape the person: behavior and brain anatomy. Nobel laureate Eric Kandel's work2 shows that when people learn new skills, their minds also affect which genes in their neurons are transcribed. Thus it is possible to shape genes to some degree through sports and exercise, which in turn shape the brain's microscopic anatomy.
The nerve cells that make up the brain are signaling devices that operate according to built-in circuits, although the circuits themselves are plastic. Their signaling capabilities underlie all aspects of mental and physical life, from the generation of thought and sensory perception to the control and execution of movement. All physical activities in sports and exercise modify the brain systems, first consciously and then unconsciously. Athletes first learn coordinated motor skills through conscious mental processes and physical repetition. The learned skills are stored in the form of short-term memory. Short-term memory is created by a functional, nonstructural modification in the ability of neurons to signal each other. For example, the neurons representing a group of muscles signal each other, after proper training, with clearer, faster, and stronger communication. Further training transforms this short-term memory into long-term unconscious memory in the synaptic connections of different brain systems. Long-term memory involves an actual structural or anatomic change in the number of signaling sites. Repetitive training causes the ability to perform a particular motor skill to be embedded in the neural circuits that produce that specific behavior. This acquired skill becomes a subconscious reflex without any conscious recollection when athletes use it. Performance of complex motor tasks, such as pitching a baseball, requires higher-order planning before the memory systems and primary motor cortex can be activated. Motor planning appears to involve many different areas of the cortex. Motor control involves a delicate balance between multiple parallel neural pathways and the recurrent feedback loops of the nervous system. Understanding the signaling properties of neurons, therefore, is essential for understanding the biologic basis of sports behavior.
Three basic principles of brain activity are crucial in sports and exercises: (1) experience changes the brain; (2) neurons that fire together wire together; and (3) neurons out of sync fail to link. First, athletes have different brains because of the exercise they have done or their general experience in sports. This principle also warns that coordination between the brains and the musculoskeletal system can be disturbed by the wrong kinds of experience, such as improper exercise or musculoskeletal imbalance or injury. The brain responds to body exercise, as do muscles. The second principle indicates that the athletes have different brains because of special connections between the neurons of their brains. The body has an ordered "map" in the brain (Fig. 3-1 and Fig. 3-2). For a particular sport, coordination between certain groups of muscles and powerful
Primary motor cortex
Primary motor cortex
Supplementary motor area
Primary motor cortex
Primary motor cortex
Supplementary motor area
output from these muscles are needed. Repetitive training builds up and solidifies the neuronal connection between the parts of the brain map representing these muscles. These neuronal connections are wired together and fire together during exercise. The third principle is a reminder that wrong kinds of physical experience will erase the brain connection built by good experience. The wrong kinds of experience may include improper training or training with fatigued or injured muscles. If one part of the connection fires more slowly than others, as in the case of musculoskeletal fatigue from overtraining or injuries, the coordinated movement is disturbed or even destroyed. Athletes should perform only with coordinated and well-balanced physical systems and without pain or injuries.
Human beings have about 100 billion neurons. Each neuron can have as many as 1300 synapses (connections) with other neurons. The human cortex alone has 30 billion neurons and is capable of making 1 million billion synaptic connections. The number of all possible neural circuits is astronomical: 10 to the power of 1 million. These staggering numbers explain the complexity of the human brain, the most complicated known structure in the universe. Through these potentially massive microstructural modifications of the synaptic connections, the brain is capable of performing so many different mental functions and behaviors. Different systems of the brain connect with each other in larger aggregates, and their functions tend to become integrated, yielding new functions. Physical performance depends on such higher-order integration within the brain systems and between the brain and the body.
Physical exercise and sports involve the following processes. People consciously learn new motor skills by repetition and unlearning of old habits. After a certain number of repetitions, the new motor skills activate and strengthen related neuronal connections in the brain, so the skills are stored as short-term memory. Further training of these skills creates or modifies the neuronal connection in different parts of the brain. Once the brain map and circuit of the new skills are built, the skills become a long-term memory stored in different brain systems. This circuit formation is the result of repetitive training, and it is activated first in conscious stages and eventually in subconscious stages. When a motor skill is performed, it must first be planned; the planning occurs by activation, both conscious and subconscious, of brain circuits. This planning happens rapidly in the premotor cortex, which then sends commands to the neuromusculoskeletal system, which in turn executes the command according to the brain's directions by activating muscles and joints. During the action, the brain systems monitor motor and sensory feedback from the body and refine the execution of the action. Once it is finished, other brain circuits will be activated to start a new action. An example is gait: activity shifts from one group of muscles to another, as electro-myography shows.
This is a highly coordinated mind-body interaction and is mostly subconsciously reflexive rather than consciously reflective. As training progresses, the muscles and joints become more coordinated so that they execute the planned order more smoothly, moving exactly according to the directed amount, no more and no less. The execution is precise, fast, clear, efficient, and powerful. This, in turn, solidifies the brain's circuit. In the presence of injury or a preinjury condition such as mus-culoskeletal fatigue, the execution is no longer so precisely coordinated nor so fast, clear, efficient, or powerful. In these circumstances, peripheral systems such as muscles and joints cannot execute the commands from the brain according to stored memory, and the subconscious reflexive coordination between the brain and the body is disturbed.
For example, if an athlete has lower back pain, the movement of his or her limbs is much slower and the range of motion of joints is limited because of fatigue or injury in the core muscles. If the condition persists, the feedback to the brain may unlearn or erase the previously stored memory to adjust to the fatigued or injured systems. This may lead to a handicapped performance and require more training to relearn the previous coordination and restore subconscious memory.
How do these physical activities affect the brain? So far, the data collected are from research on musicians. Studies of musicians who play stringed instruments have shown that the more they practice, the larger are the brain maps for their active left hands. The neurons and maps that respond to the type of sound produced by strings increase in number. In trumpeters, the neurons and maps that respond to "brassy" sounds multiply. Brain imaging shows that several areas of musicians' brains—the motor cortex and the cerebellum, among others— differ from those of nonmusicians. Imaging also shows that musicians who begin playing before the age of 7 years have larger brain areas connecting the two hemispheres. In people who meditate and meditation teachers, the insula—the part of the cortex that is activated by paying close attention— is thicker. Because of the plastic nature of the brain, not everyone uses the same areas of the brain for the same activities. As a result of this plasticity, the range of human activities is vast.
Research has revealed that exercise stimulates the production and release of brain-derived nerve growth factor (BDNF), a neuronal growth factor that redesigns the brain and plays a crucial role in influencing the brain's plasticity.2 Even natural movement of the limbs, repeated consistently, stimulates the growth of new neurons. Exercise stimulates the sensory and motor cortices and maintains the brain's balance system. In addition, a healthy heart, healthy blood vessels, and a good diet invigorate the brain.
After the right kind of training, the neurons in the brain are better arranged for particular activities. When people are motivated to learn, the brain responds plastically. As brain maps get bigger, the individual neurons become more efficient in two stages. Research data clearly demonstrate that as a monkey is trained to use its fingers, its brain map for the fingertip grows and takes up more space. After awhile, the individual neurons within the map become more efficient, and eventually fewer neurons are necessary to perform the task. As neurons are trained and become more efficient, they can process faster. This means that the speed at which people think is itself plastic. Speed of thought is essential in competitive sports and provides great benefits even in daily life. Research on animals also reveals that as an animal is trained at a skill, not only do its neurons fire faster but also their signals become clearer. Faster neurons are more likely to fire in sync with each other and become better team players. These neurons wire together more and form groups that produce clearer and more powerful signals, and powerful signals, in turn, have greater influence on the brain's physiology and structure.
Another important mind-body interaction is related to close attention, which is essential for long-term plastic change. In fact, lasting changes occur only when close attention is paid. Research has demonstrated that when people perform tasks automatically, without particular attention, the repetition will change brain maps, but the changes will not last. The ability to work on several tasks simultaneously does not build long-term memory. Attempting to learn new things with divided attention does not contribute to long-term change in brain maps.3
Physical training consists of learning new skills and unlearning old habits. Improving and refining sports skills involves the mental and physical processes of learning and unlearning, and the two processes involve different chemistry in the brain. When people learn a new skill and turn it into long-term memory, neurons in the brain fire together and wire together to form new connections, and a chemical process called long-term potentiation strengths the connections between the neurons. When the brain unlearns associations, old neuronal wiring is disconnected; this requires a different chemical process, long-term depression. Unlearning and weakening connections between neurons is just as plastic a process, and just as important, as learning and strengthening them. If people were capable of only building connections, the neuronal networks would become saturated. Unlearning skills or erasing existing memories is necessary to make room in the networks for new ones.
Nothing speeds brain atrophy more than being immobilized in an unchanging environment. The monotony undermines the dopamine and atten-tional systems that are crucial to maintaining brain plasticity.
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