health May 20, 2021
Photo by Robina Weermeijer / Unsplash

Agnosia is a rare neurological disorder characterized by loss of the ability to recognize and identify objects, faces, voices, or places, smells, or sounds. It is the inability to process sensory information.

The term 'agnosia' is derived from the Ancient Greek which means "ignorance", "absence of knowledge"
The brain has several lobes such as frontal, parietal, temporal and occipital.

Photo by Robina Weermeijer / Unsplash

• The frontal lobes are responsible for problem solving and judgment and motor function.

• The parietal lobes are involved with sensation, handwriting, and body position.

• The temporal lobes are involved with memory and hearing.

• The occipital lobes contain the brain's visual processing system.

Parietal, temporal, or occipital lobes of the brain store memories of the uses and importance of familiar objects, sights, and sounds and integrate memory with perception and identification. These lobes also store semantic information and language


Agnosia is caused by damage or lesions  to the parietal, temporal, or occipital lobe of the brain. Other conditions such as strokes, head trauma, or encephalitis, dementia, brain cancer, states of anoxia (loss of oxygen supply to the brain) including carbon monoxide poisoning that damage or impair the brain, degeneration of areas of the brain that integrate perception, memory, and identification (Alzheimer disease, Parkinson disease) can also cause agnosia.

There are several types of agnosia which may involve any sense. Typically, only one sense is affected and the type of agnosia is identified by the part of the brain that is affected.

Auditory agnosia
The inability to identify objects through sound such as a ringing telephone is known as Auditory agnosia.
In the case of auditory agnosia, even though hearing is usually normal, people may feel difficulty  in distinguishing speech from non-speech sounds. They also feel difficulty in distinguishing environmental and non-verbal auditory cues.

There are two types of auditory agnosia: semantic associative and discriminative agnosia.
Semantic associative agnosia is associated with lesions to the left hemisphere, whereas discriminative agnosia is associated with lesions to the right hemisphere.

Auditory verbal agnosia
Auditory verbal agnosia is also known as pure word deafness. Any lesion in the right temporal region causes Auditory verbal agnosia.

Autotopagnosia is the loss of the ability to visually orient or recognize the parts of one's own body.
Damage to the left parietal lobe of the brain can cause this condition.

It is the lack of awareness of the existence of a deficit or lack of insight into an existing deficit. Patients with anosognosia may refuse to accept their deficit, insisting that nothing is wrong even when one side of their body is completely paralyzed. When shown the paralyzed body part, patients may deny that it is theirs.

Environmental agnosia
These individuals experience difficulty with learning routes. They are unable  to locate a specific room or building that one is familiar with, and also unable  to provide directions for how to arrive at a particular location.This form of agnosia is often associated with lesions to the bilateral or right hemisphere posterior regions. It is also associated with prosopagnosia and Parkinson's disease.

Finger agnosia
It Is the inability to distinguish the fingers on the hand. It is due to the presence of lesions in the dominant parietal lobe, and is a component of Gerstmann syndrome.

Gustatory agnosia
It is the inability to identify objects through taste.

Olfactory agnosia is the inability to identify objects through smell.

Pain agnosia
Also referred to as congenital analgesia,and it is the difficulty in perceiving and processing pain; thought to underpin some forms of self injury.

It is also known as face blindness and facial agnosia: Patients cannot consciously recognize familiar faces, well-known faces, including those of close friends, sometimes even including their own. This is often misperceived as an inability to remember names. Damage to the inferotemporal lobe can cause Prosopagnosia.

Phonagnosia is the inability to recognize and identify familiar voices. It develops when the brain suffers damage to a certain part of the sound association region. There’s usually association with a lesion in the right half of the brain.

Social-emotional agnosia
Also referred to as expressive agnosia, the person is unable to identify facial expression, and body language and social interaction can be limited.

Somatosensory agnosia
Patients with this type of agnosia have difficulty in identifying a familiar object such as key, safety pin that is placed in the hand. However, when they look at the object, they immediately recognize and can identify it.

Tactile agnosia
Tactile agnosia is the inability to recognize objects by touch.

Time agnosia
It is the loss of comprehension of the succession and duration of events.

Visual agnosia
Generally, the occipital lobe assembles incoming visual information and the parietal and temporal lobes allow us to understand the meaning of this information.

If any brain damage occurs along the pathways that connect the occipital lobe of the brain with the parietal or temporal lobe, it will cause Visual agnosia. It is an inability to name or describe the use for an object placed in front, even though the person is able to reach for it and pick it up.


The National Institute of Neurological Disorders and Stroke (NINDS) is providing support  for research for rare diseases like agnosia.
Different types of therapies can help reverse the effects of agnosia.  However, there is no clear cure for agnosia at this time.

  • Various forms of treatment such as compensatory strategies with alternate modalities, verbal strategies, alternate cues and organizational strategies, occupational therapy or speech therapy can help patients  to compensate for their deficits.
  • Alternative medicine can also be used such as using  tactile information in replacement of visual information in the case of visual agnosia and recognizing  the individuals from their speech as in the case of an individual with prosopagnosia .
  • After knowing its cause, Agnosia can also be treated by surgery and/or antibiotics for cerebral abscess, surgery and/or radiation for brain tumors.
  • Occupational and speech therapy can help improve symptoms and help patients learn to compensate for their deficits.
  • lifestyle changes and supportive care can help people with agnosia learn to cope with their symptoms.
  • Physicians may recommend people with agnosia to get sensory information through other senses, to cope with their symptoms.


By avoiding smoking, stress and anxiety, maintaining a healthy diet and regular checkups, the occurrence of this disease can be prevented.


A. Sandhya

M.Sc Zoology

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