Agnosia

Agnosia is an impaired ability to recognize objects, as a result of brain damage, in the absence of primary sensory disorders, attention or intellectual impairment.

Agnosia occurs with damage to the associative sensory fields of the cerebral cortex. It can be observed in dementia, Alzheimer’s disease, brain injuries, meningitis, encephalitis, stroke, brain tumors, hereditary diseases, etc.

The following types of agnosias are distinguished:

Visual agnosias

In visual agnosias, recognition of visual stimuli is impaired.
The following forms are distinguished:

Object agnosia – the recognition of objects through vision is impaired. In some cases, the patient recognizes the individual parts, but cannot synthesize them into a complete image. The damage is in the parieto-occipital areas, most often bilaterally.

In other cases, the patient distinguishes the general configuration, but cannot recognize and make sense of what is seen. The damage is in the middle and inferior temporal gyrus bilaterally or on the left.

Prosopagnosia – recognition of human faces is impaired.

Color agnosia – the ability to recognize colors and the association between the object and its characteristic color is impaired. Color vision is preserved. Occurs with damage in the occipito-temporal areas.

Letter agnosia (alexia) – the recognition of written speech symbols is impaired, due to which the patient cannot read and understand written speech. He can, however, write spontaneously or under dictation, which is why the condition is also called alexia without agraphia .

Auditory agnosias

Non-verbal auditory agnosia – objects are not recognized by their characteristic sounds. It is due to bilateral superior temporal lesions.

Amusia – loss of the ability to recognize familiar melodies. The damage is most often in the temporal gyrus.

Speech auditory (verbal) agnosia (verbal deafness) – the recognition of speech sounds and words is impaired. The patient does not understand spoken speech, cannot repeat words and write under dictation. However, he can speak, write and read correctly. It is due to bilateral damage to the associative auditory cortex.

Aprosody – there is a violation in the prosody of the speech – stress, intonation, pitch, tempo.

Tactile agnosias (stereognosias)

Tactile agnosia is impaired recognition of objects by touch. The patient cannot determine what the object is, but can describe it.

Somatoagnosias

Somatoagnosia is a disorder of the perception and image of one’s own body. Unilateral and bilateral somatoagnosias are observed.

Unilateral somatoagnosias – the perception of one body half, more often the left, as one’s own is disturbed and there is a lack of care for it.
Bilateral somatognosias – recognition of parts of both halves of the body, for example fingers (finger agnosia), is impaired.

Spatial violations

Visual-spatial agnosias. Patients cannot orient themselves in space, and in severe cases they get lost, they cannot find their way home, even to their room. They are observed in dementia.

Simultanagnosia – the perception of several objects at the same time is impaired. Clove:
– dorsal – part of Ballint’s syndrome. The patient cannot fixate more than one object in the field of vision and it is very difficult to move in space.

– ventral – a milder form, in which the perception of more objects at the same time is delayed, but not impossible.

Unilateral visuospatial ignoring. It manifests itself by ignoring one half of the space, most often the left. The patient does not draw on the left half of the sheet, does not read the left side of the book.