Rediscovering tactile agnosia.

Eighty-four patients with damage to various levels of the nervous system, ranging from the peripheral nerves to the cerebral cortex, underwent somesthetic assessment in order to determine the degree to which basic and complex perceptual and motor disorders affect tactile object recognition (TOR) and to determine whether TOR can be impaired in the absence of more basic sensorimotor imperception. The results suggest that (1) basic and intermediate disorders of somesthetic function impair TOR but are commensurately more severe for any given degree of TOR impairment in patients with peripheral lesions than in patients with cortical lesions; (2) neither hemiparesis nor hemianopia alone precludes normal TOR; (3) hemineglect contributes substantially to TOR impairment; (4) impairment of TOR can occur in the absence of more basic somesthetic dysfunction and constitutes tactile agnosia; (5) tactile agnosia is a subtle, nondisabling disorder that should be distinguished from the nonagnosic, severe and disabling disorder, astereognosis; and (6) tactile agnosia results from unilateral damage to parietotemporal cortices, possibly including the second somatosensory cortex, in either hemisphere.