Astereognosis

ASTEREOGNOSIS (from the Greek a- negative particle, stereos- solid, and gnosis- knowledge), a disorder of the stereognostic sense, i.e., the recognition of an object by palpation. Astereognosis is observed: 1) in disorders of peripheral and deep sensitivity, especially the muscular sense, due to insufficient perception of external stimuli; 2) in disorders of the synthetic function of the brain (elementary sensitivity may be preserved), since peripheral stimuli alone are insufficient for recognizing an object, and their comparison with previously received stimuli corresponding to the given object is necessary; only then do mental representations of the object and its recognition arise. True astereognosis, without sensory disturbance, is a characteristic symptom of a lesion of the cerebral cortex in the lower part of the middle third of the central gyri near the Rolandic sulcus.