Brain and Language:
1. The Human Brain: The brain is the most complex organ of the body. The surface of the brain is the cortex, often called “gray matter,” consisting of billions of neurons (nerve cells) and glial cells (which support and protect the neurons). The cortex is the decision-making organ of the body. It receives messages from all of the sensory organs, initiates all voluntary and involuntary actions, and is the storehouse of our memories and the seat of our consciousness. It is the organ that most distinguishes humans from other animals. Somewhere in this gray matter resides the grammar that represents our knowledge of language. The brain is composed of a right and a left cerebral hemisphere, joined by the corpus callosum, a network of more than 200 million fibers.
2. The Localization of Language in the Brain: In the early 19th century, Franz Joseph Gall proposed the localization theory, which is the idea that different cognitive abilities and human behaviors are localized to specific parts of the brain. He also introduced a pseudoscientific theory called "organology" which later became known as phrenology, which is the practice of determining personality traits, intellectual abilities. Gall's view that the brain is not a uniform mass, and that linguistic and cognitive abilities are functions of localized brain areas, has been confirmed by scientific research on brain disorders and over the last two decades.
3. Aphasia: The study of aphasia has been an important area of research in understanding the relationship between the brain and language. Aphasia is the neurological term for any language disorder that results from acquired brain damage caused by disease or trauma. In the second half of the nineteenth century, significant scientific advances were made in localizing language in the brain based on the study of people with aphasia. In the 1860s the French surgeon Paul Broca proposed that language is localized in the left hemisphere of the brain, and more specifically in the front part of the left hemisphere (now called Broca’s area).
4. Split Brains: In people who have had split-brain surgery, the two hemispheres appear to be independent, and messages sent to the brain result in different responses, depending on which side receives the message. Studies of split-brain patients have also shown that when interhemispheric visual connections are severed, visual information from the right and left visual fields is confined to the left and right hemispheres, respectively. Because of the crucial endowment of the left hemisphere for language, written material delivered to the right hemisphere cannot be read aloud if the brain is split, because information cannot be transferred to the left hemisphere.
5. Dichotic listening: Dichotic listening is an experimental technique that uses auditory cues to observe the behavior of individual hemispheres of the human brain. Subjects listen to two different sound signals simultaneously through headphones. They can hear a curl in one ear and a girl in the other, or a cough in one ear and a laugh in the other. When asked to say what they heard in each ear, subjects were more likely to report linguistic stimuli (words, nonsense syllables, etc.) delivered directly to the right ear, but more likely to report nonverbal stimuli (musical chords, ambient sounds, etc.) delivered to the left ear. Such experiments provide strong evidence for lateralization.