STEREOOGNOSIA: ORIGIN, CONCEPT, TEST, DISORDERS - ANATOMY AND PHYSIOLOGY - 2025

The estereognosia, also called stereognosis, is the ability of humans to recognize an object in common use, using only the sense of touch.

Stereoognosia is possible thanks to three types of sensitivity. These are tactile, kinesthetic, and haptic. The first refers to skin perception through touch, the second refers to the information provided by the muscles and tendons and the third combines the previous two.

Source: Image taken from Daza J. (2007). Clinical functional evaluation of human body movement. Editorial Médica Panamericana. Edited image.

That is why it can be said that stereognosia is the reflection of motor sensory perception from the tactile point of view.

In the medical field there are neurological examination tests that evaluate superficial, deep and mixed sensory capacity. If you want to evaluate stereognosia, you should look for tests that measure mixed sensitivity, also called discriminative or cortical.

For the test to be valid, it is essential that the object or objects used during the test are known to the patient, that is, they must know their name, their function and their characteristics.

That is, the brain must have previous information stored to identify it. For this reason, the test must use common objects, frequently used by any human being.

There are neurological disorders that can cause loss of stereognosia. These are caused by injuries to the cerebral cortex, a peripheral nerve, the spinal cord or at the level of the thalamus. The first cause causes a much more severe affectation than the rest.

Origin and concept

The term stereognosia comes from the union of two Greek roots, such as stereós that means solid and gnosis that means knowledge, and gnosis refers to the ability of the brain to perceive a sensation and transform it into perception, the latter allows interpreting the information collected through the senses.

Therefore, it can be said that stereognosia is the ability to perceive through touch the characteristics necessary to recognize an object, without using any other additional sense.

The characteristics that guide the recognition of an object are: shape, size, consistency, texture, among others. This sensation is perceived thanks to the presence of the Meissner corpuscles.

Test to evaluate stereognosia

It is one of the exploratory tests that evaluates cortical sensitivity. The patient's eyes will be covered and asked to try to recognize commonly used objects just by feeling them with their hands.

Before starting the test, a practice can be done with the eyes open so that the patient becomes familiar with the procedure but not with the object, because for the practice one will be used that will not be used in the test.

Once the patient has understood the test, his eyes are covered and the test begins. If the patient is able to recognize all objects, it is said that his stereognosia is intact, but if on the contrary he is not able to recognize them, the patient is said to suffer from astereognosia.

In the first stage of the test, you are asked to describe the characteristics of the object and in the second stage, you are asked to say the name of the object. Objects can be used, such as: keys, coins, rings, screws, cutlery.

To quantify the test, proceed as follows. 11 objects will be used. Each hit is worth 2 points. If the patient does not identify it but at least gives some characteristics, he accumulates 1 point, while if he cannot get it right or describe anything, it is valued as zero points.

It is considered normal to reach a range between 20 and 22 points, below 20 the stereognosia is deteriorated.

It should be noted that Gaubert and Mockett recommend this technique to evaluate post-stroke patients. These authors indicate that the test has a moderate to high sensitivity.

Other test modalities to assess stereognosia

Another way to test is by packing a box. In it the objects will be introduced and a hole will be left to put the hand. The patient must reach in his hand, take an object and try to identify it. The patient will need to issue a result before removing it from the box. Then he extracts it and the examiner will know if he was right or wrong.

Another way to do it is to show the patient a card with the figure that we want to be extracted from the box. Suppose you are shown a card with scissors drawn, the patient must discriminate between all the objects in the box and take out the one that is being asked.

It is important to note the time it takes to recognize the object and the number of hits, as these are data that can help the diagnosis.

A related disorder: a

This disorder is also known as primary somatosensory cortex syndrome, other authors describe it as tactile agnosia.

It is very common for the abnormality to be accompanied by other sensory alterations, such as agrafesthesia, loss of discrimination between two points, loss of sense of positions, among others.

It is also possible that they may coincide with other types of agnosias, such as visual.

If the only disorder is tactile agnosia, the patient can lead an almost normal life, as this does not prevent him from developing properly in the environment. This causes that this affectation is undervalued and little diagnosed.

- Categories

The syndrome of the primary somatosensory cortex consists of a complex somatosensory lack of control. It is divided into three categories:

Amorphognosis

It is called like this when the individual loses the ability to recognize the shape or size of an object.

Ahilognosia

The individual is unable to describe the weight, density, temperature, and texture of an object. Therefore, it is not able to identify what material it is made of.

Tactile asymbolism

When it is impossible for the individual to recognize an object even though he can describe its shape, size, texture, but still cannot correctly identify it.

For example, if we give a spoon as an element to identify, the patient will tell us, it is cold, smooth, light, hard, long and thin, but he will not be able to associate it with the covered.

For this reason, some authors defend the theory that the problem of astereognosia is due to memory loss, rather than perception, even more so when they observe that Alzheimer's patients suffer from poor memory and astereognosia.

- Causes

The most frequent cause is injury to the parietal cortex, but there may be other causes, such as: thalamic injuries and injuries to the spinal cord.

Lesion of the parietal cortex

Lesions at this level usually cause astereognosia, almost always unilateral. When the damage is in the parietal cortex, the manifestations are more serious.

If the ventral portion of the cortex is affected, tactile perception is affected, but if the dorsal cortex is affected, the problem will be more cognitive.

Spinal injuries

There are several syndromes with injuries to the spinal cord, such is the case of posterior cord syndrome. This is characterized by the suffering of paresthesia (tingling sensation), itching, a feeling of puffy skin.

In these patients, flexion of the neck causes a sensation of electric shock (Lhermitte's sign). There may also be incoordination of movements (ataxic syndromes).

When examining these patients with exploratory tests, what stands out in the first instance are alterations in discriminative sensitivity, especially astereognosia.

Thalamic injuries

Dejerine-Roussy syndrome or thalamic syndrome originates from lesions in the thalamus at the level of the inferior and lateral nuclei. The lesions can be caused by a cerebrovascular accident, by metabolic, inflammatory, neoplastic or infectious problems.

This disorder is characterized by paresthesia, sensitivity disorder in the middle of the body (hemihypoesthesia), increased perception of pain (hyperalgesia), abnormal perception of pain (allodynia), incoordination of movements on one side of the body (hemiataxia) and astereognosia.

Other disorders associated with astereognosia

Among them, we can mention Alzheimer's, Gerstmann syndrome or Verger-Dejerine syndrome.

References

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2. Cost C. The processing of somatosensory information and the functionality of the hand in patients with Acquired Brain Injury. Doctoral work. 2016; Rey Juan Carlos University. Available at: pdfs.semanticscholar.org/
3. Carrillo-Mora P, Barajas-Martínez K. Basic neurological examination for the general practitioner. Rev. Fac. Med. (Mex) 2016; 59 (5): 42-56. Available at: scielo.org.
4. Garrido Hernández G. Tactile perception: anatomical considerations, psycho-physiology and related disorders. Journal of Medical-Surgical Specialties, 2005; 10 (1): 8-15. Available at: Redalyc.org
5. Daza J. (2007). Clinical functional evaluation of human body movement. Editorial Médica Panamericana. Available at: books.google.com.