The 5 types of agnosia and their symptoms

Brain injuries often cause cognitive deficits that affect a specific sensory modality, such as sight or touch.

When these problems are due to lack of recognition of stimuli, the diagnosis of "agnosia" is used. In this article we will describe the 5 types of agnosias: visual, auditory, tactile, bodily and motor.

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What are agnosias?

Agnosia is defined as inability to process certain kinds of sensory stimulation. Depending on the cognitive systems that are affected, deficits in different functions may appear, for example in the recognition of visual information, in the execution of sensorimotor patterns or in the understanding of the language.

Agnosias generally appear as a consequence of brain injuries; are very common in those resulting from ischemic strokes, neurological disorders such as dementias or traumatic brain injury, particularly when the regions where the occipital lobes and the occipital lobes meet temporary.

In these disorders the perception of stimuli is not altered in itself

, but rather the problem is located in a higher stage of the perceptual process: it is associated with memory (more specifically with recovery) of specific keys that allow us to relate the information we perceive with that we have stored in the memory.

The term "agnosia" comes from classical Greek and can be translated as "absence of knowledge" or "of recognition". It was coined by Sigmund Freud, the father of psychoanalysis, in 1891, but pioneers of the neuropsychology such as Carl Wernicke or Heinrich Lissauer had theorized around similar concepts in previous decades.

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Main types of agnosias

The most common is that agnosias occur in a single sensory modality. Therefore it is useful to divide the main classes of agnosias and their corresponding subtypes depending on whether they fundamentally affect the perception of visual information, that of sounds, touch, motor patterns or the perception of our own body.

1. Visuals

Most visual agnosias consist of deficits in the recognition of objects through sight without any involvement of the sensory organs. The most famous case of visual agnosia is probably the one that gave the title to "The Man Who Mistook His Wife for a Hat," the neurologist Oliver Sacks best-seller.

This class of agnosias usually occurs due to lesions in the left occipital lobe or in any of the temporal lobes. We can divide visual agnosias into two categories: the apperceptive ones, in which there are problems to categorize objects, and the associative ones, characterized by the inability to name them.

Prosopagnosia, which consists of a deficit in face recognition (but is also associated with trouble naming animals or car brands, for example), it is the most associative type of visual agnosia known. As for the apperceptives, simultagnosia is worth noting, in which the elements are processed properly but not the whole.

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2. Auditory

In auditory agnosia, recognition problems occur in relation to sound stimuli. Although when the brain lesions that cause agnosia are very important, the deficits can have a general nature, the most common is that they affect only the a type of auditory stimulation, such as receptive language or music (amusia).

Auditory verbal agnosia, also known as "pure deafness for words", is one of the most relevant agnosias within this category. In these cases, the affected person has difficulty distinguishing the sounds of speech from rest of auditory stimuli that it perceives, or to recover the meaning of the sets of phonemes.

3. Tactile or somatosensory (astereognosias)

Tactile or somatosensory agnosia can be defined as a inability to identify objects through touch, based on aspects such as its texture or its size, despite the fact that there are no sensory alterations. Another name for this type of disorder is "astereognosia."

A clinically significant subtype is digital agnosia, which specifically affects finger recognition. It usually occurs in conjunction with agraphia, acalculia, and left-right disorientation in the context of Gerstmann syndrome, caused by lesions in the lower part of the parietal lobe.

4. Motor (apraxia)

The term "motor apraxia" is used very infrequently due to the great popularity of one of its synonyms: "apraxia." Apraxias consist of difficulties in remembering and executing motor schemes learned intentionally; however, the same movements can appear spontaneously in their natural contexts.

Three main types of motor agnosia have been described: ideational apraxia, in which there are difficulties in carrying out sequences of movements, ideomotor, characterized by the inability to carry out actions in response to a verbal request, and the constructive one, which consists of problems to build shapes or to draw figures.

5. Bodily

In bodily agnosia there is a inability to identify one's own body. We speak of somatognosia when the problems are related to the whole body, of hemiasomatognosia if they appear only in one of its halves and of autotopagnosia in cases in which the person is able to spatially locate the parts of his Body.