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

Abstract

Disorders of tactile object recognition (TOR) may result from primary motor or sensory deficits or higher cognitive impairment of tactile shape representations or semantic memory. Studies with healthy participants suggest the existence of exploratory motor procedures directly linked to the extraction of specific properties of objects. A pure deficit of these procedures without concomitant gnostic disorders has never been described in a brain-damaged 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 under the condition of spontaneous exploration. Tactile exploration of shapes was disorganized and exploratory procedures, such as the contour-following strategy, which is necessary to identify the precise shape of an object, were severely disturbed. However, recognition of 2D shapes under manually or verbally 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 hand showed preserved activation of the spared primary sensory cortex in the right hemisphere. We interpret the deficit of our patient as a pure tactile apraxia without tactile agnosia, i.e. a specific inability to use tactile feedback to generate the exploratory procedures necessary for tactile shape recognition.

Modulation of somatosensory perception by motor intention

“…This limb-dependent alteration in perceptual experience is also accompanied by a significant decrease in the BOLD response within the parietal operculum (SII) following stimulation to the moving arm relative to the nonmoving arm. This result is consistent with the previous finding of a reduced BOLD response in SII for self-produce somatosensory stimulation (Blakemore et al, 1998) but runs somewhat counter to the fact that the parietal operculum, particularly SII, has been linked to sensorimotor integration and tactile object recognition functions; and to previous reports that SII activation is increased during tactile attention and manual exploration tasks (Burton, 2001;Nelson, 1996;Valenza et al, 2001). For example, it is known that SII increases its activity more than SI when sensory stimulation is coupled with a motor task (Huttunen et al, 1996), and lesions to SII impair can tactile object recognition while leaving basic somatosensory functions remain intact (Valenza et al, 2001).…”

Predictive coding accounts of shared representations in parieto-insular networks

“…Mima et al (1999) demonstrated that human SII and ventral premotor cortex (PMv) of humans are activated during active finger movement and Binkofski et al (1999) underlined that the activation of SII-PMv is particularly strong during hand-manipulation tasks in which complex object manipulation in comparison to simple object manipulation. Moreover, patients with tactile apraxia and tactile agnosia caused by damaging unilateral parieto-temporal cortices in either hemisphere, possibly including SII, exhibit abnormal hand-manipulation (Caselli, 1991;Valenza et al, 2001). In non-human primates, SII and the adjacent posterior insular cortex (pIC) show multiple digits and hand representations (Robinson and Burton, 1980;Krubitzer et al, 1995;Fitzgerald et al, 2004).…”

Generalized movement representation in haptic perception.

“…The optimal reference frame depends on the task at hand. For example, to identify an object one must combine the successively touched parts into a coherent whole, and it has been shown that exploratory movement sequences play an essential role in this process (Valenza et al, 2001). To reach an object, one must locate it in egocentric space.…”