Apraxia(redirected from Cogan's oculomotor apraxia)
Also found in: Dictionary, Thesaurus, Medical.
An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. The apraxic person knows the act to be carried out, and has the requisite sensory-motor capacities, yet performance is defective. The abnormality is highlighted when the act must be performed on demand and out of context. Defects in performance vary from total inability to initiate the action, to incorrect serial ordering of elements, to partial approximations. A common apraxic behavior is the use of a body part as an object. Pantomiming the act of brushing the teeth, for example, a person may run the index finger across the teeth as though it were a toothbrush, while in normal performance, the hand assumes the posture of holding and moving the brush.
Apraxia is usually observed in both upper extremities. When it occurs unilaterally, it is usually the left arm and hand that are affected. This has been explained by assuming that the left cerebral hemisphere is specialized in the organization of voluntary movements, just as it is in language. The left hand is under the immediate control of the right hemisphere, but for skilled voluntary actions, the right hemisphere is dependent on information transmitted from the dominant left hemisphere over the corpus callosum. Callosal lesions produce apraxia of the left hand, because the right hemisphere is incapable of organizing the plan of movement independently. With an appropriately placed left-hemisphere lesion, a bilateral apraxia will result. When the left-hemisphere lesion also destroys the primary motor zone, the right arm is paralyzed and the apraxia is masked. The observable apraxia on the left side is referred to as sympathetic apraxia. This is seen in many individuals with right hemiplegia (unilateral paralysis of the body) and Broca's aphasia. Another apraxia often coupled with Broca's aphasia is nonspeech oral apraxia (or buccofacial apraxia). Individuals with this disorder can be observed to struggle to perform such simple acts as protruding the tongue or licking the lips on command or imitation, even though these movements are executed easily as part of the act of eating. See Aphasia, Hemispheric laterality
There are several disorders that are controversial with regard to their interpretation as forms of apraxia. The nonfluent speech pattern of Broca's aphasia, often riddled with speech-sound errors, is considered as apraxia of speech by some authorities, while others view it as an integral part of the linguistic deficit of the aphasia. In dressing apraxia and in some types of constructional apraxia, the defect appears to be perceptually based. Limb-kinetic apraxia is widely interpreted today as a mild spastic paresis, while ideational apraxia, commonly associated with dementia, is likely due to conceptual confusion rather than to a disturbance of motor organization. See Agnosia
the inability to execute purposeful movements and actions, occurring in consequence of disorders of various sections of the cerebral cortex. Apraxia is evident in cases of brain tumors, softening of parts of the brain as the result of nutritional deficiencies, encephalitis, and other disorders. There are several kinds of apraxia, depending on the sites that have been affected.
Spatial apraxia occurs when the occipital and lower sincipital regions have been affected. Spatial orientation becomes disrupted and the patient cannot distinguish between right and left sides, vertical and horizontal positions, and so forth. He finds it difficult to copy geometrical figures containing asymmetrically placed elements. These optical-spatial disorders come under “constructive” apraxia, or apractic agnosia. Kinesthetic apraxia occurs in diseases of the sincipital region (the rear sections of the central convolutions) of the left hemisphere in consequence of disruption of the conduction of nerve motor impulses. The patient is unable to pick up an object, fasten a button, or tie a shoelace. In oral apraxia the motor foundation of speech is disrupted. The patient cannot imitate lip and tongue movements. Dynamic apraxia is observed in disorders of the postfrontal sections of the cerebral cortex, which are located to the front of the central convolutions. The patient is unable to smoothly perform habitual operations requiring the use of both hands. He finds it difficult to change from one movement to another. Frontal apraxia occurs in disorders of the frontal lobes of the cerebral cortex and is characterized by inertia of voluntary movements and actions. For example, the patient may be induced to make a fist which he cannot always voluntarily relax. Plans of action and the sequence of separate links in the action become disrupted. In attempting to light a cigarette, the patient will light a match and bring it toward his mouth. The treatment must be directed at eliminating the causes of apraxia.
Z. IA. RUDENKO