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Stereognosis is the ability to recognize and identify common objects through tactile manipulation without the use of visual cues. Conversely, difficulty in recognizing items by touch when primary sensory modalities (e.g., pain, temperature, and vibration) are intact is termed astereognosis or tactile object agnosia.
Astereognosis is a type of tactile agnosia.
Lesions to the somatosensory cortex, specifically the postcentral gyrus of the parietal lobe are implicated in the development of astereognosis, with damage usually being expressed contralaterally (Campbell, 2005; DeMyer, 2003; Husain, 2002; Roland, 1976; Tomberg & Desmedt, 1999). Because the vast majority of healthy individuals can identify common objects by touch, even one mistake on a test for stereognosis may be pathognomic of cerebral dysfunction (Dean & Davis, 2007).
Testing for stereognosis commonly includes blindfolding the patient, and then having them identify a series of commonly known shapes, items, or objects solely by manipulating them in their hand. Examples of assessment objects include keys, paperclips, coins, and buttons (Dean & Woodcock, 2003; Reitan & Wolfson, 2002). Such tasks are considered effective screeners because they test the entire sensory pathway, beginning with the finger tips all the way through to the parietal lobes and their cortical and subcortical connections (Bauer & Demery, 2003).
While diagnosis of astereognosis is not difficult, addressing treatment options can be complicated by the fact that difficulty in identifying objects through manual manipulation can stem from a number of problems not necessarily related to a primary somatosensory deficit. Imaging research using functional MRI techniques has shown multiple areas of activation in the brain during tactile object recognition tasks, implicating not only the parietal somatosensory region but also the visual association cortex and the frontal polar cortex (Deibert, Kraut, Kremen, & Hart, 1999). Such findings may suggest that tactile object representation includes multiple networks of cortical pathways, including those necessary for motor, visual, and lexical processing. Deficits in any of these pathways could result in difficulty with tactile object recognition. Other deficits, including memory disorders, dysnomia, dementia, nerve damage, spinal cord damage, and motor deficits, can all contribute to symptoms that manifest as difficulty in recognizing and identifying shapes through touch (Bauer & Demery, 2003; Campbell, 2005; Husain, 2002; Ropper & Brown, 2005). Because of this, evidence of astereognosis must be carefully reviewed and differentially diagnosed from other disorders that might mimic the effects of astereognosis when considering treatment options.
References and Readings
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