Why are cerebral hemispheres so convoluted

One idea is that some areas of the cortex simply grow more and rise above other areas, creating the gyri. Another idea is that groups of highly interconnected neurons in the cortex are mechanically pulled close to each other by the threadlike axons that make up the white matter.

However, evidence suggests that neither of these two ideas is correct. The third idea is that the gray matter grows more than the white matter, leading to a "buckling" that gives the cortex its shape, the researchers said. But earlier attempts to model this buckling were not successful, the researchers said. In previous studies, researchers assumed that the gray matter is a thin, stiff layer growing atop of a thick, soft base of white matter, but this assumption yielded wrinkles that aren't like the ones in real human brains.

In the new study, the researchers assumed that the gray and white matter have similar stiffness, but different growth rates. Using mathematical simulations, they showed that depending on the size of the brain, their model results in different shapes of brain surfaces.

Normally, we are not aware of the different roles that our two hemispheres play in day-to-day functions, but there are people who come to know the capabilities and functions of their two hemispheres quite well. In some cases of severe epilepsy, doctors elect to sever the corpus callosum as a means of controlling the spread of seizures Figure 2.

After surgery, these split-brain patients show a variety of interesting behaviors. However, they are able to recreate the picture with their left hand, which is also controlled by the right hemisphere. When the more verbal left hemisphere sees the picture that the hand drew, the patient is able to name it assuming the left hemisphere can interpret what was drawn by the left hand.

Figure 2. Much of what we know about the functions of different areas of the brain comes from studying changes in the behavior and ability of individuals who have suffered damage to the brain. For example, researchers study the behavioral changes caused by strokes to learn about the functions of specific brain areas. A stroke, caused by an interruption of blood flow to a region in the brain, causes a loss of brain function in the affected region. The damage can be in a small area, and, if it is, this gives researchers the opportunity to link any resulting behavioral changes to a specific area.

The types of deficits displayed after a stroke will be largely dependent on where in the brain the damage occurred. Consider Theona, an intelligent, self-sufficient woman, who is 62 years old.

Recently, she suffered a stroke in the front portion of her right hemisphere. As a result, she has great difficulty moving her left leg. Theona has also experienced behavioral changes. For example, while in the produce section of the grocery store, she sometimes eats grapes, strawberries, and apples directly from their bins before paying for them.

This behavior—which would have been very embarrassing to her before the stroke—is consistent with damage in another region in the frontal lobe—the prefrontal cortex, which is associated with judgment, reasoning, and impulse control.

Watch this video to see an incredible example of the challenges facing a split-brain patient shortly following the surgery to sever her corpus callosum. Watch this second video about another patient who underwent a dramatic surgery to prevent her seizures. Improve this page Learn More. Skip to main content. Search for:. Brain Hemispheres Learning Objectives Explain the relationship between the two hemispheres of the brain.

The brain is the crown jewel of the human body. For centuries, scientists and philosophers have been fascinated by the brain, but until recently they viewed the brain as nearly incomprehensible. Now, however, the brain is beginning to relinquish its secrets. Scientists have learned more about the brain in the last 10 years than in all previous centuries because of the accelerating pace of research in neurological and behavioral science and the development of new research techniques.

As a result, Congress named the s the Decade of the Brain. At the forefront of research on the brain and other elements of the nervous system is the National Institute of Neurological Disorders and Stroke NINDS , which conducts and supports scientific studies in the United States and around the world. This fact sheet is a basic introduction to the human brain.

It may help you understand how the healthy brain works, how to keep it healthy, and what happens when the brain is diseased or dysfunctional. The brain is like a committee of experts. All the parts of the brain work together, but each part has its own special properties. The brain can be divided into three basic units: the forebrain , the midbrain , and the hindbrain. The hindbrain includes the upper part of the spinal cord, the brain stem, and a wrinkled ball of tissue called the cerebellum 1.

The cerebellum coordinates movement and is involved in learned rote movements. When you play the piano or hit a tennis ball you are activating the cerebellum. The uppermost part of the brainstem is the midbrain, which controls some reflex actions and is part of the circuit involved in the control of eye movements and other voluntary movements. The forebrain is the largest and most highly developed part of the human brain: it consists primarily of the cerebrum 2 and the structures hidden beneath it see " The Inner Brain ".

When people see pictures of the brain it is usually the cerebrum that they notice. The cerebrum sits at the topmost part of the brain and is the source of intellectual activities. It holds your memories, allows you to plan, enables you to imagine and think. It allows you to recognize friends, read books, and play games. The cerebrum is split into two halves hemispheres by a deep fissure.

Despite the split, the two cerebral hemispheres communicate with each other through a thick tract of nerve fibers that lies at the base of this fissure. Although the two hemispheres seem to be mirror images of each other, they are different. For instance, the ability to form words seems to lie primarily in the left hemisphere, while the right hemisphere seems to control many abstract reasoning skills.

For some as-yet-unknown reason, nearly all of the signals from the brain to the body and vice-versa cross over on their way to and from the brain. This means that the right cerebral hemisphere primarily controls the left side of the body and the left hemisphere primarily controls the right side.

When one side of the brain is damaged, the opposite side of the body is affected. For example, a stroke in the right hemisphere of the brain can leave the left arm and leg paralyzed. Each cerebral hemisphere can be divided into sections, or lobes, each of which specializes in different functions. To understand each lobe and its specialty we will take a tour of the cerebral hemispheres, starting with the two frontal lobes 3 , which lie directly behind the forehead.

When you plan a schedule, imagine the future, or use reasoned arguments, these two lobes do much of the work. One of the ways the frontal lobes seem to do these things is by acting as short-term storage sites, allowing one idea to be kept in mind while other ideas are considered. In the rearmost portion of each frontal lobe is a motor area 4 , which helps control voluntary movement.

When you enjoy a good meal—the taste, aroma, and texture of the food—two sections behind the frontal lobes called the parietal lobes 6 are at work. The forward parts of these lobes, just behind the motor areas, are the primary sensory areas 7.