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Agnosia
Last reviewed: 04.07.2025
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Agnosia is the inability to identify an object using one or more of the senses. Diagnosis is based on clinical symptoms, often with neuropsychological testing and brain imaging (CT, MRI) to identify the cause. Prognosis depends on the nature and extent of the lesion and the age of the patient. There is no specific treatment, but occupational therapy may help patients compensate for the condition.
[ Types of agnosia
Some types of brain damage cause different forms of agnosia, which may involve any sense. Typically, only one sense is affected; the ability to identify objects through other senses is not affected. Examples include the inability to identify objects by a perceived sound, such as a telephone ringing (auditory agnosia), taste (gustatory agnosia), smell (olfactory agnosia), touch (tactile agnosia, or astereognosis), or visual input (visual agnosia).
Other forms of agnosia involve very specific and complex processes within a single type of sensitivity. For example, prosopagnosia is the inability to identify familiar faces, including close friends, or, in other cases, to distinguish individual objects from a class of objects, despite the ability to identify facial features and objects with certain generic features.
Anosognosia often accompanies damage to the right subdominant parietal lobe. The patient denies his disease, insisting that there is nothing wrong, even when one side of the body is completely paralyzed. When shown a paralyzed body part, the patient may deny that it belongs to him, a violation of the body scheme - autotopagnosia is possible. Anosognosia is often combined with denial of paralyzed or insensitive parts of the body ("loss of half the trunk" or anosognosia of hemiplegia) or space ("loss of half space", unilateral spatial agnosia or ignoring half the space), which is typical for left-sided lesions.
Combined lesions of the occipital and temporal lobes may cause an inability to recognize familiar places - a disturbance of topographic orientation (environmental agnosia), visual impairment (visual agnosia), or color blindness (achromatopsia). Right-sided temporal lesions may cause an inability to interpret sounds (auditory agnosia) or impaired perception of music (amusia).
How is agnosia recognized?
The patient is asked to identify common objects using different senses (vision, touch, or other). If there is a suspicion of hemispace denial, the patient is asked to identify paralyzed body parts or objects in the corresponding hemispace. Neuropsychological testing can help identify more complex types of agnosia. Tests should be performed to differentiate disturbances of sensation and understanding in order to distinguish such defects from agnosia.
Brain imaging (CT or MRI with or without angiography) is necessary to characterize central lesions (e.g., infarction, hemorrhage, space-occupying intracranial process) and to detect cortical atrophy characteristic of degenerative diseases. Physical examination usually reveals primary disturbances of certain types of sensory functions that may complicate further evaluation of the patient.
Treatment of agnosia
Agnosia has no specific treatment. Rehabilitation with the help of a speech therapist or occupational therapist can help the patient achieve compensation for the disease. The degree of recovery depends on the size and location of the lesions, the degree of damage and the age of the patient. Recovery occurs mostly within the first three months, but generally lasts up to one year.