Dissociated active and passive tactile shape recognition: a case study of pure tactile apraxia

Disorders of tactile object recognition (TOR) may result from primary motor or sensory deficits or higher cognitive impairment of tactile shape repres entations or semantic memory. Studies with healthy participants suggest the existence of exploratory motor procedures directly linked to the extractio n of specific properties of objects. A pure deficit of these procedures wit hout concomitant gnostic disorders has never been described in a brain-dama ged patient. Here, we present a patient with a right hemispheric infarction who, in spite of intact sensorimotor functions, had impaired TOR with the left hand. Recognition of 2D shapes and objects was severely deficient unde r the condition of spontaneous exploration. Tactile exploration of shapes w as disorganized and exploratory procedures, such as the contour-following s trategy, which is necessary to identify the precise shape of an object, wer e severely disturbed. However, recognition of 2D shapes under manually or v erbally guided exploration and the recognition of shapes traced on the skin were intact, indicating a dissociation in shape recognition between active and passive touch. Functional MRI during sensory stimulation of the left h and showed preserved activation of the spared primary sensory cortex in the right hemisphere. We interpret the deficit of our patient as a pure tactil e apraxia without tactile agnosia, i.e. a specific inability to use tactile feedback to generate the exploratory procedures necessary for tactile shap e recognition.