What is Agnosia?
Agnosia is a rare brain disorder in which a person cannot use their senses to identify particular objects or people. The condition is usually caused by an injury or event that damages a part of the brain responsible for sensory processing.
Agnosia usually affects only one of the senses, and the sense involved depends on the location of the brain damage. In addition, the severity of the damage may also influence the severity and treatability of the symptoms.
Types of Agnosia
Agnosia may affect any of the senses, and some types of the disorder affect precise, complex sensory processes. Types of agnosia include:
- Visual agnosia. People with this type of agnosia cannot recognize objects when they see them, but they can identify them using other senses, such as touch.
- Auditory agnosia. This form of the disorder makes a person unable to identify sounds, such as a telephone’s ring.
- Somatosensory agnosia. In this type of agnosia, a person can’t identify an object by touching it but can identify the object if they can see it.
- Olfactory agnosia. People with this type can sense odors but can’t identify them.
- Gustatory agnosia. As with olfactory agnosia, people with gustatory agnosia are unable to identify tastes.
- Prosopagnosia makes a person unable to recognize familiar faces.
- Environmental agnosia causes an inability to recognize familiar places.
- Anosognosia causes a person to be unaware of a disability. For example, it may occur when a person suffers paralysis because of a stroke but cannot admit the paralysis exists.
- Simultanagnosia makes a person unable to recognize multiple objects (or multiple parts of a single object) at the same time.
What Causes Agnosia?
Agnosia is caused by an injury, medical event, or underlying disorder that causes damage to specific parts of the brain. Symptoms of agnosia arise when brain damage interferes with the normal processing of sensory input and memory.
Common causes of agnosia include:
- Traumatic brain injury
- Brain tumors
- Brain infections
- Exposure to toxins such as carbon monoxide
- Alzheimer’s disease
- Other types of progressive dementia
- Agenesis of the corpus callosum
- MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)
Is Agnosia Hereditary?
Because agnosia is caused by an injury, an underlying disorder, or brain damage from an external event, it is not directly inherited. However, some of the disorders that may underlie agnosia, such as Alzheimer’s disease, can have an inherited component. In these cases, the inherited risk for developing agnosia is linked to the risk of developing the underlying condition.
How Is Agnosia Detected?
The onset of agnosia is often rapid immediately following a brain injury or stroke. If a doctor suspects that agnosia might be present, they may ask the patient to identify everyday objects using various senses. When these primary assessments suggest agnosia, further diagnostic testing will likely be recommended.
How Is Agnosia Diagnosed?
A doctor may diagnose agnosia if sensory symptoms coincide with underlying brain damage or injury. The diagnostic process may include:
- Physical exams and neurological exams to rule out other possible causes of the symptoms
- Neuropsychologic tests to measure the patient’s executive functioning, attention, memory, language, motivation, mood and emotion, quality of life, and personality
- Magnetic resonance imaging (MRI) or computerized tomography (CT) looks for brain damage that may cause agnosia.
PLEASE CONSULT A PHYSICIAN FOR MORE INFORMATION.
How Is Agnosia Treated?
No treatment directly reverses agnosia symptoms, but the treatment of the underlying cause, if effective, may improve agnosia. The appropriate treatment depends on the underlying condition, but possible options include:
- Antibiotics to treat brain infections
- Surgery to relieve brain abscesses
- Surgery to remove brain tumors
- Radiation to reduce brain tumors
Therapies such as speech therapy or occupational therapy may help the patient find ways to cope with agnosia symptoms.
How Does Agnosia Progress?
The long-term outlook for people with agnosia varies depending on whether or not the condition’s underlying cause can be treated effectively. If agnosia symptoms are severe and the underlying condition is not reversible, agnosia can significantly negatively impact the patient’s quality of life. The likelihood of recovery from agnosia depends on several factors, including:
- The type and location of the underlying brain damage
- The severity of agnosia symptoms
- The age of the patient
- The response of the underlying condition to treatment
When recovery from agnosia is possible, symptoms usually begin to resolve in a matter of months.
How Is Agnosia Prevented?
There is no known way to prevent agnosia after the disorder-causing brain damage occurs. Steps taken to reduce the risk of head injuries, stroke, or any other potential cause of agnosia are the only way to reduce the risk of the condition.
Agnosia Caregiver Tips
- Be patient and understanding. Remember that agnosia is caused by underlying brain damage, and your loved one can’t simply stop being confused by trying harder.
- Use alternative communication methods. Use labels and signs to help your loved one identify everyday objects and places. Label pictures of familiar people.
- Make sure your loved one understands you. Explain things simply and use gestures to support the words you use. Repeat yourself if necessary, and double-check to verify that you’re being understood.
Agnosia Brain Science
The various types of agnosia are caused by damage to different parts of the brain. Researchers believe that brain damage interferes with a person’s ability to process sensory input or connect sensory information to memories that allow the person to identify what they’re sensing.
Types of agnosia associated with specific areas of the brain include:
- Visual agnosia (occipital lobe)
- Auditory agnosia (temporal lobe)
- Somatosensory agnosia (parietal lobe)
- Olfactory agnosia (temporal lobe)
- Gustatory agnosia (temporal lobe)
- Prosopagnosia (inferotemporal lobe)
- Anosognosia (right parietal lobe)
- Environmental agnosia (occipital or temporal lobe)
Title: Orientation Agnosia: Clinical and Anatomical Study (AGNORIENT)
Principal investigator: Olivier Martinaud
The area of the brain responsible for visuospatial processing data and, more specifically, the orientation of an object or image, is located in the parietal lobe, especially on the right side. Therefore, dysfunction of this region would result in a disorder of recognizing the orientation of objects and images that the investigators call orientation agnosia. Several isolated cases are reported in the literature, but to the investigators’ knowledge, the deficit has never been systematically researched or put into perspective compared to other neuropsychological deficits. Moreover, the precise location of the lesion responsible for such a disorder remains uncertain. Therefore, the objectives of this study are (1) to detect the existence of orientation agnosia in the case of a right parietal lesion and (2) to improve the understanding of such a deficit allowing better management of this disorder.
Title: Brain Imaging and Pain: Analysis of Placebo Analgesia
Principal investigator: Michael E Robinson, Ph.D.
University of Florida
This study is a basic science study of the mechanisms of placebo analgesia in asymptomatic healthy individuals. Each participant receives a baseline pain testing session, followed by a conditioning paradigm that results in the expectation of pain relief and conditioning. They then undergo functional magnetic resonance imaging during either placebo (conditioned analgesia) or baseline. To examine order effects and habituation, the participants also either undergo a repeated placebo or a repeated baseline. The primary dependent measures in the study are the fMRI determined regions of interest in a network of brain areas associated with pain processing. The anticipated outcome of the study is the alteration of network connectivity between sensory, affective, evaluative areas of the brain associated with placebo.
Because this is not a traditional clinical trial, there are not traditional efficacy criteria. Instead, the outcomes are changes in brain function from manipulations of patient expectation and classical conditioning.
Title: Functional Magnetic Resonance Imaging (fMRI) of Anosognosia in Amnestic Mild Cognitive Impairment (MCI) and Alzheimer’s Disease (AD)
University of Wisconsin
This is a three-year fMRI study conducted at the University of Wisconsin (UW) Hospital and the William. S. Middleton VA Hospital. This study is guided by the hypothesis that reduced fMRI activity and connectivity cortical midline structures (i.e., medial frontal and ventral posterior cingulate cortex) are physiologic abnormalities that relate strongly to the compromised insight into cognitive deficits, or anosognosia, shown by a subset of individuals with amnestic MCI (aMCI) and AD. Further, the investigators hypothesize that these regional changes in fMRI activity are predictive of faster progression from aMCI to AD.