A loss of ability to carry out skilled movement despite adequate understanding of the task and normal motor power.
Constructional and dressing apraxia: See page 109, non-dominant parietal disease. Gait apraxia-. Difficulty in initiating walking - frontal lobe/anterior corpus callosum disease.
Oculomotor apraxia'. Impaired voluntary eye movement - parieto-occipital disease. Ideamotor apraxia: Separation of idea of movement from execution - cannot carry out motor command but can perform the required movement under different circumstances -dominant hemisphere (see later).
Ideational apraxia: Inability to carry out a sequence of movements each of which can be performed separately - frontal lobe disease.
HIGHER CORTICAL DYSFUNCTION the disconnection syndromes
Cortical function is described, on the previous pages, 'lobe by lobe'. These functions integrate by means of connections between hemispheres and lobes. Lesions of these connecting pathways disorganise normal function, resulting in recognisable syndromes -the disconnection syndromes. APRAXIA is a feature of some of these disorders.
The connecting pathways may be divided into:
/wirahemispheric: lying in the subcortical white matter and linking parts of the same hemisphere.
/«ferhemispheric: traversing the corpus callosum and linking related parts of the two hemispheres.
THE INTRAHEMISPHERIC DISCONNECTION SYNDROMES
1. Conduction Aphasia
Lesion of the arcuate fasciculus /
linking Wernicke's and Broca's *J
Characterised by: \ y Fluent dysphasic speech. Good ""-a-V v comprehension of written/spoken \ material. Poor repetition.
2. Pure word deafness
Lesion of the connection between the .
primary auditory cortex (Herschl's gyrus) /
and auditory association cortex. /
Characterised by: lis Impaired comprehension of spoken word. V'
Self-initiated language is normal. The * patient seems deaf, but audiometry is normal.
3. Buccal lingual and 'sympathetic' apraxia
Involves the links between left and right association motor cortices in the subcortical region. ^
Characterised by: Broca's area
Right brachiofacial weakness and apraxia of tongue, lip and left limb movements.
THE INTERHEMISPHERIC DISCONNECTION SYNDROMES
1. Left side apraxia
Lesion of the anterior corpus callosum with interruption of the connections between the left and right association motor cortices. Characterised by:
Apraxia of left sided limb movements,
3. Agenesis of the corpus callosum
2. Pure word blindness or alexia without agraphia
Lesion of the posterior corpus callosum and dominant occipital lobe with interruption of connections between the visual cortex and the angular gyrus/Wernicke's area. Characterised by: Inability to read, to name colours, to copy writing, but with normal spontaneous writing and the ability to identify colours.
This is a developmental disorder with no connection between the two hemispheres. Characterised by:
A failure to name an object presented visually or by touch to the non-dominant hemisphere. (The right and left visual fields cannot match presented objects.)
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