Figure Caption: The major cortical brain centers involved in the control of movement. Subcortical centers include the cerebellum, basal ganglia and substantia nigra.

Apraxia: Inability to carryout purposeful movements in the absence of paralysis or paresis.

Ideomotor Apraxia

This apraxia is associated with great difficulty in the sequencing and execution of movements. A common test of apraxia is to request the patient to demonstrate the use of a tool or household implement (e.g., "Show me how to cut with scissors"). Difficulties are apparent when the patient moves the hand randomly in space or uses the hand as the object itself, such as using the forefinger and middle finger as blades of the scissors. They have additional trouble sequencing the correct series of movements and make errors in orienting their limbs in space consistent with the desired action. Imitation of the movements of others will usually improve performance but it is still usually defective.

Memories for skilled acts are probably stored in the angular gyrus of the parietal lobe in the left hemisphere. Lesions of this area result in impairment of the execution of motor acts and the patients cannot recognize the correct motor expressions of others. However, the motor execution of skilled acts is mediated by the motor control areas of the frontal lobes. If these areas are lesioned or disconnected from the motor memories in the angular gyrus then the patient also has difficulty expressing the actions but can recognize the correct motor expressions of others. This results in two manifestations of ideomotor apraxia.

Ideational Apraxia

Patients with ideational apraxia cannot perform a series of acts although they may be able to perform the individual components of the series. For example, making coffee requires filling the coffee maker with coffee, adding water then turning on the coffee maker. Patients with ideational apraxia may correctly perform each step but place them out of order, such as turning on the coffee maker first. This disorder results from loss of the conceptual knowledge associated with objects and the overall goal of the activity sequence. Ideational apraxia does not have clear localizing significance and is most often observed among patients with dementia related illnesses.

Buccofacial Apraxia

Patients with this apraxia have difficulty performing skilled movements with the lips, face, tongue, larynx, and pharynx. When asked to blow out a match, suck on a straw or blow a kiss, they appear unable to make the movements or make uncoordinated movements. They may substitute incorrect movements or perseverate. They may also substitute verbal expressions for the movement. For example, when asked to blow out a match, the patient might say "Blow". Face and mouth motor control areas in the frontal lobes probably mediate these actions. Broca's aphasia and buccofacial apraxia can exist independently, indicating that control of language expression is independent of simple movement control of the muscles in the vocal apparatus. However, to make matters more confusing, oral apraxia can exist with Wernick'e aphasia, suggesting that it is more complex than an incoordination of simple motor programs residing in the frontal lobes.

Kinetic Limb Apraxia

Patients who have this form of apraxia cannot make fine motor movements with the limb contralateral to a brain lesion. They have great difficulty performing fine movements, such as picking a coin from a table surface, but will correctly perform gross movements. Lesions of the primary sensory and motor cortex, secondary motor cortex and pyramidal tracts may cause this disorder.

Assessment

Apraxia involves the impairment of coordinated movement and action sequences. It ranges from simple actions, such as blowing out a match to following complex muli-step commands, such as those involved in following a recipe. Assessment always involves requesting the patient to execute these acts and observing the patient's performance. There are roughly three levels of ability: 1) perfomance to command (e.g. "Show me how you cut with scissors"); 2) imitation of the examiner's performance; 3) performance while actually using an object that is part of the task (e.g. holding scissors while cutting paper). Performance to command without the examiner's demonstration and without objects represents the highest level of praxis.