Tactile agnosia and tactile aphasia: symptomatological and anatomical differences.

Two patients with tactile naming disorders are reported. Case 1 (right hand tactile agnosia due to bilateral cerebral infarction) differentiated tactile qualities of objects normally, but could neither name nor categorize the objects. Case 2 (bilateral tactile aphasia after operation of an epidural left parietal haematoma) had as severe a tactile naming disturbance as Case 1, but could categorize objects normally, demonstrating that tactile recognition was preserved. Case 1 may be the first case of tactile agnosia clearly differentiated from tactile aphasia. CT scans of Case 1 revealed lesions in the left angular gyrus, and in the right parietal, temporal, and occipital lobes. Case 2 had lesions in the left angular gyrus and of posterior callosal radiations. Our findings suggest that tactile agnosia appears when the somatosensory association cortex is disconnected by a subcortical lesion of the angular gyrus from the semantic memory store located in the inferior temporal lobe, while tactile aphasia represents a tactual-verbal disconnection.