Neuroscience Clerkship

 

 

APHASIA, APRAXIA AND AGNOSIA


Aphasia is an acquired impairment in the ability to spontaneously produce, understand, and/or repeat speech. Defects in the ability to read and write also constitute aphasia. Deficits can be identified in the language syntax, semantics, and phonology. There are several classic types of aphasia (see learning objective on Broca's, Wernicke's and Conduction aphasias).


Apraxia is the inability to perform a motor activity on command in the presence of intact motor and sensory systems, comprehension, and cooperation. There are several types of apraxia:


Motor Apraxia. Motor apraxia is a disturbance of voluntary movement in which one cannot use objects for the purposes that they were designed for. However, the affected individual still knows what the object should be used for. So for example, a person with motor apraxia knows that a hammer is used to hammer a nail, but cannot use the hammer for that purpose.


Ideomotor Apraxia. Ideomotor apraxia is a disturbance of voluntary movement in which a person cannot translate an idea into movement. People with ideomotor apraxia can still perform automatic movements, such as using scissors. However, they cannot perform such movements upon request. They also cannot copy movements or make gestures.
 

Ideational Apraxia. Ideational apraxia is a disturbance of voluntary movement in which a person misuses objects because he/she has difficulty identifying the concept or purpose behind the objects. For example, it would be difficult to use a hammer if one could not identify what the purpose of a hammer was. It is important to note that motor movement is not lost in ideational apraxia. However, the person's movements appear confused because he/she cannot form a plan on how to sequence those movements when using an object.


Agnosia is an impairment of the ability to recognize, or comprehend the meaning of various sensory stimuli, not attributable to disorders of the primary receptors or general intellect. Agnosias are receptive defects.


Apperceptive Agnosia. This condition involves poor perception of form and the complaint of poor vision despite good acuity, intact perception of movement and colors. Distinguishing features of this condition are the inability to draw objects, copy figures, or distinguish different shapes. The lesion is most often localizable to the calcarine cortex.

Associative Agnosia. Patients with this condition cannot recognize objects through vision alone. They are unable to name, describe, or mimic the use of objects. Patients deny visual complaints and are able to draw, copy, and distinguish shapes. The lesion is usually bilateral and involves the inferior temporal occipital lobes including the visual association cortex.