Astereognosia and tactile agnosia: symptoms and causes

Asterognosia, also called tactile agnosiaIt is a little known disorder as it usually does not 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 alters recognition by touch.

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

    What are agnosias?

    Agnosias are a set of disorders characterized by the lack of recognition of stimuli that occur in a particular sensory modality, such as touch or hearing. In such cases the deficits are not the consequence of alterations of the sensory organs, But at higher levels of perceptual pathways.

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

    Agnosias are usually given in a single modality and are often classified according to the direction in which the alteration occurs. So that we can find visual, auditory, tactile or somatosensory, motor and bodily agnosias, Which consist of difficulty identifying the body itself 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 he can identify it by touch; in this case, we would speak of visual agnosia. Sometimes, if the brain damage caused by the alteration is very severe, various sensory modalities may be affected.

      Definition of asterognosia and tactile agnosia

      “Asterognosia” is a term commonly used to refer to tactile agnosia, that is, the inability to identify objects by touch in the absence of abnormalities in perception itself. On the other hand, stereognosis would be the basic ability that allows us to perceive and recognize such stimuli normally.

      In this type of agnosia, the person fails to retrieve from memory the information needed to identify touch-related pimples, such as temperature, texture, height, or weight. However, he is able to do this using other senses (usually sight), unless other classes of agnosia are present.

      Some authors use the denomination “Tactile agnosia” only in cases where the assignment is limited to one of the hands or at most both, whereas if the problem concerns tactile perception more generally, they prefer to speak of asterognosia. In any case, there does not seem to be a consensus around these nomenclatures.

      Asterognosia and tactile agnosia often go undiagnosed because they usually do not significantly interfere with the functioning of those who have them. This has led to an underestimation of the number of cases of asterognosia, as well as the scarcity of research in this regard detected during the review of the scientific literature.

      Causes of this disorder

      The available evidence shows that asterognosia occurs as a result of lesions in two specific regions of one of the cerebral hemispheres: the parietal lobe and the association cortex (made up of parts of the parietal, temporal and occipital lobes). It is also associated with damage to the dorsal spine or posterior spinal cord.

      The specific location of the lesions determines the peculiarities of the symptoms. In this way, when the ventral part of the cortex is damaged, the tactile perception of three-dimensional objects is particularly affected, while if the same happens in the dorsal cortex, it is more common for the recognition problems to be cognitive.

      One of the disorders most directly linked to astereognosia is Alzheimer’s disease, characterized by progressive cognitive impairment which affects memory in a particularly intense way. This association supports approaches that advocate that agnosias are above all a memory disorder, And no perception.

      Tactile agnosia, or more specifically digitalis (affecting the fingers), is also a characteristic sign of Gerstmann syndrome. In this disorder, asterognosia is accompanied by other peculiar symptoms such as difficulty navigating left and right, calculating or making graphic representations, especially writing.

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