Astereognosis

Astereognosis

Astereognosis is the failure to recognize a familiar object, such as a key or a coin, palpated in the hand with the eyes closed, despite intact primary sensory modalities. Description of qualities, such as the size, shape and texture of the object may be possible. Hence, this is a failure of higher order (i.e., cortical) processing and is associated with lesions of the posterior parietal lobe (post central gyrus) association cortex. There may be associated impairments of two-point discrimination and graphesthesia (cortical sensory syndrome). Astereognosis was said to be invariably present in the original description of the thalamic syndrome by Dejerine and Roussy.
Some authorities recommend the terms stereoanesthesia or stereohypesthesia as more appropriate terms for this phenomenon, to emphasize that this may be a disorder of perception rather than a true agnosia (for a similar debate in the visual domain, see Dysmorphopsia).

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