Language And The Brain

Language and the brain
It is ironic that until recently, progress in our understanding of brain functions has come not from the study of normal individuals but largely from the study of individuals with injured brains. Whenever disease or injury affects the left side of the brain, some aspect of the ability to perceive, process or produce language may be disturbed. Individuals with such braindisease or injury are said to be aphasic and their brain disturbances can give us insight into how the human brain carries out its language-related tasks.
Aphasia is a broad term encompassing numerous syndromes of communicative impairment.
Neurolinguists are interested in the correlation between brain damage and speech and language deficits. Of the many questions of interest for them, three arefundamental:
•Where in the brain are speech and language localized?
•How does the nervous system function to encode and decode speech and language?
•Are the components of language –phonology, syntax, semantics—neuroanatomically distinct and therefore vulnerable to separate impairment?
Where is language localized in the brain?
Language: A left hemisphere phenomenon
In 1861, Paul Brocadescribed a patient who in life had had extreme difficulty in producing speech, later, at autopsy, the patient was found to have damage in the posterior inferior part of the frontal lobe in the left cerebral hemisphere, now known as Broca’s area. Broca became the first individual to substantiate the claim that damage to a specific area of the brain results in a speech deficit. In 1865, Broca extended hisclaim about speech localization by reporting that damage to sites in the left cerebral hemisphere produced aphasia, whereas destruction of corresponding sites in the right hemisphere left linguistic capacities intact.
In 1874, Carl Wernicke published a monograph-describing patient with speech comprehension deficits who had damage (lesions) outside Broca’s area. Wernicke’s work strengthenedBroca’s claim that left hemisphere structures are essential for speech.
Today scientists agree that specific neuroanatomic structures, generally of the left hemisphere, are vital for speech and language, but debate continues as to which structures are committed to the various linguistic capacities.
In 1949, J. Wada reported that the injection of sodium amytal into the main (carotid) artery on thelanguage-dominant side of the brain induces a temporary aphasia.
In 1959, Wilder Penfield and LaMar Roberts surgically removed portions of the brain of patients to provide relief from intractable seizures in patients with epilepsy. They discovered that when electrical current was applied to a brain area involved in speech, one of two things occurred; the patient either had trouble talking or uttered avowellike cry. However, no patient ever produced an intelligible word as result of electrical stimulations. Finally, they were able to conclude that three areas of the left hemisphere are vital to speech and language: Broca’s area, Wernicke’s area and the supplemental motor area.
The nervous system
The brain and spinal cord constituted the central nervous system (CNS) and are linked to theperipheral nervous system. Impulses received from peripheral receptors are sorted, interpreted and responded to by the CNS.
Levels of the Central Nervous System
The CNS is hierarchically organized, higher structures being more complex than lower ones. At the lowest level is the spinal cord, which acts as a cable through which streams of neuronal messages between the body and the brain aretransmitted. Above the spinal cord is the brain stem. Lower nervous systems structures are primarily reflexive and controlled by higher centers. At the highest level of nervous system are the cerebral hemispheres, responsible for voluntary activity. The cerebral hemispheres emerge from the higher brain stem and are covered with a convoluted sheath of gray matter, called the cortex. The degree of...