Language Disorders

The Brain

The human brain is bilateral, meaning that there are two halves, referred to as left and right hemispheres. While this presents a rough physical symmetry, as with the human body, much study has gone into understanding the functional asymmetry of the brain hemispheres, specializations that are primarily or exclusively contributed by areas of only one side. Handedness, being dominant in the right or left hand for tool use, is one asymmetrical specialization with which most are familiar. Many additionally favor one ear or one eye. Observation and experimentation have identified many specializations regarding perceptual and productive processes that are localized within one hemisphere, or that heavily rely on particular pathways through the brain, which are often restricted to a single half of the brain.

The two hemispheres are connected or wired together by means of the corpus callosum. While the human brain has been described as functionally asymmetrical because scientists have identified many specialized regions, structures, and pathways within the brain that are localized to only one hemisphere, the corpus callosum allows these two hemispheres and their specialized areas to communicate with each other. One can think of interhemispheric communication as a secondary process. The primary perceptual and motor pathways are between each hemisphere and the opposite side of the body, or contralateral, meaning “other side.” That is why a stroke or injury to the right side of the brain sometimes results in paralysis or loss of function on the left side of the body.

In popular terms, language processing is sometimes seen as the province of the left hemisphere because injuries to the left half of the brain more often result in noticeable impairments to speech processing than injuries to the right half of the brain. Music involves regions of both hemispheres, broadly distributed, with greater variability than [Page 644]language processing, perhaps in part because of the wider range of musical exposure, experience, training, and practice. However, this is an oversimplification of the complexities and range of meanings involved in these two domains of human behavior.

The French composer Joseph-Maurice Ravel in 1914. Late in his life, Ravel was afflicted with aphasia, apraxia, and eventually amusia, which is an umbrella term to describe deficits that reduce musical abilities in isolation or in combination with other deficits affecting speech or motor skills. Prior to his illness, Ravel was one of the most prominent figures associated with Impressionist music.

Aphasia

In the late 19th century, two European researchers identified regions in the left hemisphere of the brain that seemed to provide crucial pathways for language processing. These are Broca's and Wernicke's areas, named for Carl Wernicke and Pierre Paul Broca. These regions are most associated with pathologies referred to as the aphasias, or deficits of language. There are several varieties of aphasia, which can be grouped according to the particular deficits that they exhibit or the specific regions of the brain that have caused the disorder.

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