The 5 types of agnosias (and their characteristics)

Agnosia is defined as that inability to recognize familiar stimuli and attribute meaning to them. Depending on different parameters, we find different types of agnosias.

In this article we will focus on the types of agnosias according to the sensory modality affected. We will learn about the characteristics of each one and the subtypes of agnosia that we find within each group.

The agnosias prevent us from making a correct interpretation of the meaning of the stimuli. It is not caused by sensory deficits, but by the existence of lesions in associative areas of the cerebral cortex. There are different types of agnosias depending on the criteria we choose to classify them.

Different classification criteria

Depending on the number of senses “affected”, we find unimodal agnosias (a single sense) and polymodal agnosias (more than one). On the other hand, If they only affect one side of the body, we find hemiagnosias.

Depending on the altered sensory channel, we find visual agnosias (which are the most frequent), auditory, tactile, gustatory, olfactory and somatosensory agnosias.

Finally, These may appear in isolation, or accompany other disorders. (for example, hemineglect). Let’s now see the different types of agnosias according to the sensory modality affected.

Types of agnosias according to their sensory modality

Depending on the modality that is altered, we find different types of agnosias. Let’s see the details of each of them:

Visual agnosias

Visual agnosias involve altered visual recognition. Thus, they prevent us from recognizing objects, colors, people… They occur in the absence of visual defects, and in the presence of lesions in the visual association areas.

In them there are no attention deficits either, and the person’s mental level is preserved. Visual recognition ability was preserved before the injury.

Within this group we find visual agnosias for objects, as well as other types of visual agnosia. The latter include: simultagnosia, prosopagnosia, chromatic agnosia, agnostic alexia and movement agnosias.

Auditory agnosias

Auditory agnosias lead to difficulty recognizing the meaning of acoustic stimuli. They appear as a result of lesions in the temporal lobe of the brain.

However, the primary auditory areas are preserved. There are different types of auditory agnosia, depending on whether the altered recognition is musical (called amusia), whether it is the recognition of non-verbal sounds (sound agnosia) or verbal recognition (pure verbal agnosia).

Somatosensory agnosias

Somatosensory agnosias involve a loss of the ability to recognize the physical qualities of an object by touch. Thus, it implies difficulty in determining its weight, size, shape, density or texture.

It occurs in the absence of hypoesthesia (pathological decrease in sensitivity). It appears as a consequence of lesions in the somesthetic associative cortex of the parietal lobe. Wernicke (1885) spoke of two different modalities of auditory agnosia:

Primary asterognosia: inability to recognize tactile features of an object. Secondary asterognosia or asymbolia: it would be an aserognosia itself (unlike the previous one).

Types of somatosensory agnosias

Beyond Wernicke’s classification, there are different variants of somatosensory agnosias. Thus, we find:

Tactile agnosia: prevents the recognition of objects by touch while the primary areas of the brain are preserved. Barognosia: is the inability to estimate the weight of an object due to impairments in the parietal association areas. Autotopagnosia: prevents locating and orienting the different parts of the body under orders or through imitation. Digital agnosia: loss of ability to recognize, identify, select and orient the fingers of the hand. Spatial agnosia: the inability to recognize familiar places or to orient yourself in space.

Olfactory agnosias

They involve a temporary or prolonged loss in the ability to identify odors, which is called anosmia. They are frequently underdiagnosed. Within olfactory agnosias, there are different variants:

Hyposmia: partial deficit in the ability to recognize odors. Selective anosmia: to certain substances or odors. Hyperosmia: the ability to discriminate different odors is exacerbated. Parosmia: erroneous perception of odors. It usually occurs in some brain tumors. Cacosmia: permanent sensation of bad odor.

Agnosias for diseases

Within the agnosias for diseases we find different types of them. Between them: anosognosia, asomatognosia, anosodiaphoria, misoplegia, somatoparaphrenia and analgoagnosia. What does each one consist of?

Anosognosia

It is the lack of awareness of sensory, motor, cognitive or linguistic deficits. They occur as a consequence of brain damage in people with various psychiatric pathologies or dementia.

Asomatognosia

It is the denial of a part of the body corresponding to the hemiplegic area. It is characteristic of patients with hemineglect syndrome.

Anosodiaphoria

It is a form of light asomatognosia. It is characterized by the lack of sufficient awareness of the neurological disease, although the patient does not deny its existence. It is also known as the beautiful indifference.

Misoplegia

Misoplegia is exacerbation of the feeling of neurological disease. It is characterized by responses of hatred or rejection of the paralyzed limb.

Somatoparaphrenia

It is the distorted perception of neurological disease. It is characterized by the attribution of the injured limb to another person.

Analgoagnosia

It is defined as the inability to understand pain despite the fact that there is no hypoesthesia in the face of painful stimuli. An asymbolism occurs in the face of nocioceptive stimuli, that is, the meaning of the stimulus is unknown.

As we have seen, the field of neuropsychology and neurology is as mysterious as it is interesting. There are a large number of symptoms, stimuli and disorders that we are unaware of, and that suffer from people who have suffered a brain injurywhich includes agnosias of all kinds.

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