Astereognosia and tactile agnosia: symptoms and causes

Astereognosia, also called tactile agnosiaIt is a little-known disorder because it does not usually affect the lives of people who suffer from it in a very negative way. It is a type of agnosia (that is, a disorder in the identification of objects that is not due to sensory alterations) that specifically impairs recognition through touch.

In this article we will describe the most significant clinical features and the most common causes of astereognosia or tactile agnosia. Before proceeding we will dwell briefly on the concept of agnosia, since it is important to adequately contextualize astereognosia and compare it with other disorders of the same class.

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What are agnosias?

Agnosias are a group of disorders characterized by the lack of recognition of stimuli that are presented in a certain sensory modality, such as touch or sound ear. In these cases the deficits are not the consequence of alterations in the sense organs, but at higher levels of the perceptual pathways.

This type of symptom generally appears as a consequence of lesions that damage the cerebral cortex, interfering with the transmission of sensory impulses to pathways related to recognition aware. Some of the most common causes of agnosia include ischemic strokes and neurodegenerative diseases.

In general, agnosias occur in only one modality, and they are often classified according to the direction in which the alteration occurs. So, we can find visual, auditory, tactile or somatosensory, motor, and body agnosias, which consist of difficulties in identifying one's own body or a part of it, often one of the halves.

An example of this type of disorder would be the inability to recognize that the object in front of the person is a towel through sight, although they could identify it by touch; in this case we would speak of visual agnosia. Sometimes, if the brain damage caused by the disturbance is very severe, several sensory modalities may be affected.

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Defining astereognosia and tactile agnosia

"Astereognosia" is a term that is commonly used to refer to tactile agnosia, that is, to the inability to identify objects through touch in the absence of abnormalities in perception itself same. On the contrary, stereognosis would be the basic ability that allows us to perceive and recognize this type of stimuli in a normal way.

In this type of agnosia, the person cannot recover from the memory the information needed to identify touch-related stimulus cues, such as temperature, texture, size, or weight. However, it is capable of doing so when using other senses (usually sight), unless other kinds of agnosia are present.

Some authors use the name “tactile agnosia” only in cases where the affectation is limited to one of the hands or at most two, while if the problem involves tactile perception in a more general way they prefer to speak of astereognosy. In any case, there does not seem to be a consensus around these nomenclatures.

On many occasions, astereognosia and tactile agnosia are not diagnosed because they do not usually significantly interfere with the functioning of those who suffer from them. This has led to an underestimation of the number of cases of astereognosia, as well as the paucity of research in this regard that is detected when reviewing the scientific literature.

Causes of this disorder

The available evidence reveals that astereognosia appears as a consequence of lesions in two specific regions of any of the cerebral hemispheres: the parietal lobe and the association cortex (composed of parts of the parietal, temporal, and occipital lobes). It is also associated with damage to the dorsal or posterior column of the spinal cord.

The specific location of the lesions determines the peculiarities of the symptoms. Thus, when the ventral part of the cortex is damaged, the tactile perception of objects is especially affected. three-dimensional, while if the same thing happens in the dorsal cortex, it is more common for recognition problems to have a cognitive character.

One of the disorders that is most directly related to astereognosia is the disease of Alzheimer's, characterized by a progressive cognitive deterioration that affects in a particularly intense way the memory. This association supports the approaches that defend that agnosias are primarily a memory disorder, and not perception.

Tactile agnosia, or more specifically digital (affecting the fingers), is also a characteristic sign of Gerstmann syndrome. In this disorder, astereognosia occurs with other peculiar symptoms such as difficulties in orient themselves between left and right, to calculate or to make graphic representations, especially for write.