Apraxia is a disorder of brain function in which a person is unable to perform learned motor acts even though the physical ability exists and the desire to perform them is there. Brain damage to the parietal lobes, particularly in the dominant hemisphere, results in apraxia. Unlike paralysis, movements remain intact but the patient can no longer combine them sequentially to perform desired functions like dressing. Damage to the parietal lobes can arise from a variety of causes including metabolic diseases, stroke, and head injuries.
The German neurologist Hugo Liepmann (1863-1925) introduced the term apraxia in 1900 after observation of an impaired patient. Based on anatomic data, he suggested that planned or commanded actions are controlled not in the frontal lobe of the brain but in the parietal lobe of the brain's dominant hemisphere. Liepmann then postulated that damage to this portion of the brain prevents the activation of "motor programmes," learned sequences of activities that produce desired results on command. He also divided apraxia into three types: ideational, ideomotor, and kinetic.
Ideational apraxia, sometimes called object blindness, renders patients incapable of making appropriate use of familiar objects upon command, even though they can name the object and describe how to use it. Ideomotor apraxia is the inability to follow verbal commands or imitate an action, such as waving goodbye. The harder the patient tries, the more difficult execution becomes. Ironically, the patient often performs the gesture spontaneously or as an emotional response, like waving goodbye when a loved-one leaves. Kinetic apraxia refers to clumsiness in performing a skilled act that is not due to paralysis, muscle weakness, or sensory loss.
Other types of apraxia have been described since Liepmann's time. Apraxia of speech is the inability to program muscles used in speech, resulting in incorrect verbal output. It is frequently seen in conjunction with aphasia, the inability to select words and communicate via speech, writing, or signals. In dressing apraxia, patients can put clothes on but cannot program the appropriate movement sequences. Therefore, a coat goes on back-to-front, or socks over shoes. Facial apraxia leaves patients unable to move portions of their face upon command. They often, however, use other parts of their body to achieve a similar end. For example, when asked to blow out a match, the patient may step on it. Constructional apraxia refers to the inability to apply well-known and practiced skills to a new situation, like drawing a picture of a simple object from memory.
Although intense research has increased scientific understanding of this complex disorder, many mysteries remain.
Brown, Jason W., Aphasia, Apraxia and Agnosia, Clinical and Theoretical Aspects. Springfield, IL: Charles C. Thomas, 1979.
Brown, Jason W., ed. Agnosia and Apraxia: Selected Papers of Liepmann, Lange, and Potzl. Mahwah, NJ: Lawrence Erlbaum Associates, 1988.
Hammond, Geoffrey R., ed. Cerebral Control of Speech and Limb Movements. Amsterdam: North-Holland, 1990.
Roy, E. A., ed. Neuropsychological Studies of Apraxia and Related Disorders. Amsterdam: North-Holland, 1985.
Williams, Moyra. Brain Damage, Behavior, and the Mind. New York: John Wiley & Sons, 1979.
Marie L. Thompson