Broca's area

Broca's area is a region of the human brain responsible for the coordination of words and speech. The area was discovered by its namesake, Pierre Paul Broca, a nineteenth-century doctor who studied the brains of patients with severe language disabilities. Broca's area is located in the frontal lobe of the left hemisphere of the brain. Researchers believe the region processes sensory information from other parts of the brain and coordinates it with motor-controlling sections responsible for mouth movements. Damage to the region does not affect language comprehension but may cause a person to have difficulty forming words or speaking coherently.

Background

The human brain is an organ that acts as the control center for the body. It oversees both voluntary and involuntary functions, such as regulating heart rate and breathing, coordinating movement, and processing sensory information. The brain is divided into several sections, each with its own specialized responsibilities. The oldest part of the brain is called the brain stem, a section that connects the upper sections of the brain to the spinal cord. The brain stem is responsible for many automatic body functions such heartbeat, breathing, and digestion. The second largest section of the brain is the cerebellum. It is located near the back of the brain and is responsible for coordinating muscle movements, motor control, and balance.

The uppermost and largest section of the brain is the cerebrum, which is responsible for more complex brain functions such as vision, speech, learning, and fine motor skills. The cerebrum is divided by a deep fissure that separates the brain into right and left hemispheres that oversee different functions. For example, the right hemisphere is generally more creative, focusing on artistic skills, three-dimensional recognition, and visual comprehension; the left hemisphere is more logic based, with a focus on math, science, language skills, and analytic thought. Each hemisphere is also further divided into four sections, or lobes, each with its own specialized functions. The outer layer of the cerebrum is known as the cerebral cortex, which is a folded network of nerve cells called neurons. Neurons are specialized cells that transmit electrochemical instructions to the rest of the body. The cerebral cortex contains about 70 percent of the brain's neurons.

Overview

In the mid-nineteenth century, scientists were at odds over how the human brain functioned. Some thought the body utilized the entire brain to oversee functions, while others thought that tasks were localized in certain sections of the brain. In 1861, Pierre Paul Broca, a French neurologist and proponent of the localization theory, began seeing a patient named Louis Victor Leborgne. Leborgne was a fifty-one-year-old man with epilepsy who had suffered from a severe speech disability for twenty years. Leborgne could not communicate in a normal fashion, but could only utter the syllable tan. After Leborgne's death from other causes, Broca autopsied his brain and discovered a damaged area, or lesion, in his left frontal lobe.

A few months later, Broca came into contact with Lazare Lelong, an eighty-four-year-old man with a similar condition to Leborgne. Lelong had lost his ability to speak a year earlier and could only manage a five-word vocabulary consisting of the French words for yes, no, always, three, and an attempt to say his name. When Broca examined Lelong's brain after his death, he found a lesion in the same region as in Leborgne's brain. These two discoveries led Broca to deduce that speech was localized in a specific section of the brain and any damage to that section would severely limit the ability to speak. Broca termed the condition, aphémie, or the loss of articulated speech. Broca continued his neurological work until his death in 1880. The area of the brain he studied was eventually named after him as was the condition of aphémie, which became known as Broca's aphasia.

Broca's area is located in the frontal lobe of the cerebral cortex just above and behind the left eye. It was later discovered the region works in tandem with another part of the brain called Wernicke's area, named after Carl Wernicke, the German neurologist who discovered it in 1876. Wernicke's area is located near the parietal and temporal lobes at the rear of the brain. The two areas are connected by a bundle of nerve fibers called the arcuate fasciculus. Researchers had long known Broca's area was associated with forming articulate speech while Wernicke's area was associated with language comprehension; however, the exact nature of the relationship was unknown until the twenty-first century. Patients suffering from Broca's aphasia are capable of understanding language and ideas but have difficulty with verbal communication; patients with Wernicke's aphasia can speak with a full vocabulary but have trouble comprehending language and often speak incoherently.

In 2015, researchers at Johns Hopkins University School of Medicine in Baltimore, Maryland, and the University of California, Berkeley, discovered that Broca's area is neurologically active in the moments before words are spoken and enters a resting state as a person is speaking. The researchers used a technique monitoring electrochemical activity to map the flow of information through the brain. They found that Broca's area interacts with the temporal lobe of the cerebral cortex, a region responsible for sensory input and organization as well as language comprehension. As the temporal lobe absorbs the input, Broca's area becomes active as it processes and coordinates the information, formatting it into verbal communication before passing it along to the motor cortex. The motor cortex is the section of the brain that handles voluntary responses, such as the proper mouth movements necessary for speech. Scientists hope that continued study of Broca's area and the speech process could help in the treatment of language disabilities caused by epilepsy, stroke, and brain injuries.

Bibliography

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