Astereognosis
Definition and Clinical Testing
Astereognosis (also known as tactile agnosia) is the neurological failure to recognize a familiar object palpated in the hand while the eyes are closed. For a diagnosis of true astereognosis, the patient's primary sensory modalities—such as light touch, pain, temperature, and vibration—must remain intact. The patient may even be able to accurately describe the physical qualities of the object, such as its size, shape, temperature, and texture, but remains entirely unable to synthesize this information to name or recognize the object itself.
Clinically, stereognosis is tested by asking the patient to close their eyes and extending their hand. The examiner places a familiar, everyday object (like a coin, key, or paperclip) into the patient's palm and asks them to manipulate and identify it. Inability to do so indicates astereognosis.
Astereognosis is tested by asking a patient to identify a familiar object, such as a key or coin, using only their sense of touch while their eyes are closed.
Pathophysiology and Anatomical Correlates
Astereognosis represents a failure of higher-order (cortical) sensory processing and integration. It is most classically associated with lesions of the contralateral posterior parietal lobe, specifically involving the superior parietal lobule and the somatosensory association cortex located just behind the postcentral gyrus.
Because it is a cortical sensory deficit, astereognosis is frequently accompanied by other features of a "cortical sensory syndrome," including impairments in two-point discrimination and graphesthesia (the ability to recognize writing on the skin).
While parietal lesions are the most common cause, astereognosis can also occur with deep subcortical lesions. Notably, it was described as being invariably present in the original description of the thalamic syndrome by Dejerine and Roussy (Dejerine-Roussy syndrome), which results from infarction of the posterior thalamus.
Terminology and Clinical Debates
The exact nosological classification of astereognosis is a subject of debate among neurologists and neuropsychologists. Some authorities argue that it is not a true agnosia (which implies a pure disconnection between intact perception and memory/meaning). Instead, because the spatial and structural synthesis of the object is often subtly impaired, they recommend using the terms stereoanesthesia or stereohypesthesia to emphasize that this is fundamentally a disorder of complex tactile perception rather than a pure associative agnosia. This mirrors a similar debate in the visual domain regarding dysmorphopsia versus visual agnosia.
Cross References
Agnosia; Dysmorphopsia; Graphesthesia; Two-point discrimination