Autotopagnosia (body-image agnosia) is the inability to correctly orient or perceive different body parts; patients cannot obey commands to point to parts of their own or the examiner's body (e.g., foot, hand, nose). The responsible lesion is usually, though not always, in the tem-poroparietal region (angular and supramarginal gyri). An aphasic patient may appear to have au-totopagnosia because he cannot understand verbal instructions, but aphasia may also coexist with true autotopagnosia. Finger agnosia is the inability to identify, name, or point to fingers. These patients cannot mimic the examiner's finger movements or copy finger movements of their own contralateral hidden hand with the affected hand. Right-left disorientation is the inability to distinguish the right and left sides of one's own or another's body; these patients cannot obey a command to raise their left hand or touch it to their right ear. This type of disorientation can cause dressing apraxia (p. 128) and similar problems.
Anosognosia is the unawareness or denial of a neurological deficit, such as hemiplegia. Patients may claim that they only want to give the paralyzed side a rest, or attempt to demonstrate that their condition has improved without realizing that they are moving the limb on the unaffected side. Most such patients have extensive lesions of the nondominant hemisphere. Anosognosia may also accompany visual field defects due to unilateral or bilateral lesions of the visual cortex (homonymous hemianopsia, cortical blindness). The most striking example of this is Anton syndrome, in which cortically blind patients act as if they could see, and will even "describe" details of their surroundings (incorrectly) without hesitation.
Constructional apraxia is characterized by the inability to represent spatial relationships in drawings, or with building blocks. Affected patients cannot copy a picture of a bicycle or clock. Everyday activities are impaired by the inability to draw diagrams, read (analog) clocks, assemble pieces of equipment or tools, or write words in the correct order (spatial agraphia). Hemineglect is the inability to consciously perceive, react to, or classify stimuli on one side in the absence of a sensorimotor deficit or exceeding what one would expect from the severity of the sensorimotor deficit present. Hemineglect may involve unawareness of one side of the body (one-sided tooth brushing, shaving, etc.) or of one side of an object (food may be eaten from only one side of the plate, eyeglasses may be looked for on only one side of the room). When addressed, the patient always turns to the healthy side. Neurological examination reveals that double simultaneous stimulation (touch, finger movement) of homologous body parts (same site, e.g., face or arm) is not felt on the affected side (extinction phenomenon). In addition, perception of stimuli on the affected side is quantitatively lower than on the healthy side, there is limb akinesia despite normal strength on the side of the lesion, and spatial orientation is impaired (e. g., the patient copies only half of a clock-face).
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