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This page will provide you with a comprehensive overview on the etiology of agnosia, the symptoms of agnosia and the treatment for agnosia. Specifically, this discussion will focus on the relationship between agnosia and stroke. We sincerely hope that our website helps to further your understanding on the topic of both agnosia and stroke. If you have further questions, please contact a healthcare professional.
What is Agnosia and Stroke?
Agnosia is as rare condition in which a person is unable to recognize various stimuli such as objects, persons, smells, and sounds, but is still able to detect sensory information. Simply put, it is when an individual has a “perceptual impairment” whereby their primary sensory processing abilities (their ability to detect the stimuli) are normal but their ability to connect it to parts of the brain that store information is not. It is important to note that this does not mean the patient is suffering from significant memory loss or mental disabilities.
Typically in cases of agnosia only a single modality is affected. As such, pateints can often compensate through their other abilities. For example, if a patient has a problem connecting visual stimulus information, they may be able to use other means of processing the information, such as tactile stimulus. With this in mind, it is easy to understand how agnosia can be differentiated from other conditions that result from brain damage, such as apraxia, which affects many modalities. Another important differentiating factor is the location of damage. Agnosia is commonly associated with lesions in the parietal and temporal lobes of the brain. This is significant insofar as semantic information is stored in these lobes.
The lesions in apraxia are caused by any type, or combination, of brain injury. These include, but are not limited to stroke, poisoning, head trauma and dementia. Although agnosia is uncommon there is a correlation between agnosia and stroke. This is because ischemia often causes brain cell death. Moreover, the depletion of oxygen (hypoxia) from a stroke can lead to lesions in any of area of the brain. When these lesions are located in areas that integrate accumulated sensory information with memory recall it results in agnosia.
Types of Agnosia
Each of our 5 senses has distinct pathway of into our brain. Resultantly, there are many different types of agnosia that can occur. In other words, the variability between the different types of agnosia is due to the fact that both agnosia and stroke can occur in different areas of the brain. Some types of agnosia that demonstrate a strong correlation between agnosia and stroke include:
Is an inability to perceive motion. This produces an effect whereby the individual perceives moving objects as a series of still images.
Is one of the most common types of agnosia and clear demonstrates the correlation between agnosia and stroke. It occurs when a person has brain damage in the pathways that connect the occipital lobe to the parietal and temporal lobes. More specifically, visual agnosia is the inability to understanding visual stimuli.
There are two subtypes that can occur:
Apperceptive Visual Agnosia: Is caused by lesions on both sides of the brain. In cases of apperceptive visual agnosia, patients have difficulty assembling an entire image. That is to say that they do not understand how objects relate to one another. As such, they cannot make sense of the larger scene. However, it is important to note that this does not affect the individual’s ability to move around in their environment.
Associative Visual Agnosia: Occurs when a person cannot understand information associated with an object, such as the object’s name or use. One important factor that differentiates associative visual agnosia from apperceptive agnosia is if the person is able to sketch an object, but cannot say what it is.
Prosopagnosia: This form of agnosia is when a person cannot recognize faces. Specifically, the person has incurred damage to the fusiform face area (FFA). Although a correlation is not typically made between prosopagnosia and stroke, it can be found in individuals with autism or dementia.
Agnosic Alexia (Pure Alexia):
In cases of pure alexia, patients are unable to recognize words visually. In other words, the individual can speak and write without difficulty, but cannot read.
Pure Word Deafness: Also referred to as auditory agnosia, wherein a patient is unable understand spoken language and is unable to repeat words. Ostensibly this condition can appear to be deafness however, it is important to note that the individual can still hear, read, write and recognize environmental stimuli.
Autotopagnosia: Is caused by damage to the left parietal lobe. In cases of autopagnosia, a patient is unable to localize or orient parts of their body. That is to say that a patient cannot pinpoint certain body parts oftentimes pointing to surrounding areas, but not the body part they have been asked to locate.
There are a number of instances wherein different types of agnosia demonstrate a strong correlation between agnosia and stroke. The manifestation of symptoms and classification of a specific type of agnosia is largely dependent on the location of the stroke lesion in the brain.
Symptoms of Agnosia
The symptoms of agnosia depend upon which type of agnosia the patient has. For example, if a patient has visual agnosia then they will be able to see objects but not be able to recognize them by sight. Importantly, a patient’s motivation, intelligence or attention will not be affected. This is an important consideration because, as elucidated earlier, agnosia affects only one modality, and thus, it can help rule out other potential conditions, such as autism.
Diagnosis of Agnosia
Diagnosis of agnosia is typically clinical and involves various psychophysical tests to determine which process is disrupted in the patient. Importantly, because stroke can cause widespread brain damage, agnosia and stroke are typically not the only conditions that exist in the patient.
The doctor first verifies that the individual’s condition is not actually from a loss of sensation. They do this through a physical examination and by ensuring that the patient can communicate. The communication aspect is important because if a person has a condition, such as aphasia (a communication disorder), the doctor may incorrectly diagnose their expressions and it can interfere with the testing process.
The doctor then asks the patient to identify various objects through the use of their different senses. For example, the doctor may place a pen in the patient’s hand and ask them what it is. The ultimate goal is to see if the patient can associate the appropriate word with the object. If the doctor cannot use this process to diagnose the patient, they will investigate further by using neuropsychological testing and brain imaging.
Neuropsychological testing can also be used to help the doctor determine the specific modality affected and as a confirmatory measure. Likewise, brain imaging can be used to characterize the lesion and check for atrophy in different areas of the brain. Two important tests they may preform include: a CT (computed tomography) scan or a MRI (magnetic resonance imaging) scan.
Treatment for Agnosia
The treatment for agnosia is largely comprised of therapy and rehabilitation. For example, occupational therapy and speech therapy can help improve patients with speech problems. However, it is important to note many individuals with agnosia do not actually know the extent of their condition because they do not seek out medical help. This may be because of another related disorder, anosognosia (lack of awareness of a deficit). This perceptual impairment may cause an individual to fail to recognize that something is wrong and prevent them from getting medical help. For this reason, it is crucial for a person to be properly diagnosed by a medical professional. The most important aspect in the treatment of agnosia is to eliminate the cause, if possible. This is especially true if it is related to a tumor of some sort.
For any additional information on agnosia and stroke, please contact your local healthcare professional.