Dysphasia occurs when something, usually a lesion or injury to the brain, disrupts the connection between human thought and human language production. This is not the same as a sensory impairment (blindness or deafness) and therefore can be a little more difficult to diagnose and to differentiate from other cognitive impairments--such as memory loss, dementia or schizophrenia. Receptive language dysphasia has particular symptoms.
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Patients suffering from receptive language dysphasia will still be able to produce speech in a near-fluent manner, but the speech itself will be a "word-salad"--a jumble of meaningless or disconnected words. This is also a symptom of schizophrenia. However, schizophrenic patients will also display manic behaviour and other serious mental illnesses, whereas dysphasic patients only have difficulty with their speech facilities, not any other mental processes.
Receptive vs. Expressive Dysphasia
The line between receptive and expressive dysphasia (also commonly referred to as aphasia), in practice, is often blurred. In theory, receptive aphasics can produce fluent speech sounds (e.g., "my father go went where bathroom door being to"), but there is no meaning to the sentences. In addition, receptive aphasics have difficulty comprehending language, whether spoken or written. Expressive aphasics can comprehend language that is spoken to them or written for them to read, but they have difficulty producing speech. Their sentences make sense, but are broken up by repeated pauses and stutters, and they have difficulty forming grammatically correct verb tenses (for example, if they wanted to say their father went to the store yesterday, their speech might sound something like: "uh... my... dad... uh... go... the store... yesterday").
Types of Receptive Dysphasia
There are several subtypes of receptive dysphasia. The most well known is Wernicke's aphasia, which is caused by lesions in the Wernicke's area of the brain. Wernicke's area is responsible for comprehension, word retrieval and semantic content of language. Thus, damage to this area leaves the patient unable to comprehend speech, but still able to produce it.
Transcortical sensory aphasia can cause similar symptoms, such as impaired comprehension and frequent nonsensical words in speech, but the symptoms are in general less severe. The patient can form coherent sentences some of the time, and he may be aware when he begins to produce a word-salad.
Global aphasia is the most severe form of aphasia. It occurs when there is extensive damage to the left hemisphere of the brain, and generally results in both receptive and expressive dysphasia. The patient is normally unable to comprehend or produce speech.
One of the most common tests for receptive dysphasia involves asking patients to read aloud words from a written passage, and then asking the patient to explain the passage. Then she would be asked to listen to a recorded, spoken-word passage,and to explain what the passage discussed. If the patient is unable to verbally express comprehension of either spoken or written passages, a nonverbal test of comprehension may be performed. For example, the doctor may hand the patient a sheet with pictures of items on it and then ask the patient to point to the red ball. If the patient is suffering from receptive dysphasia, she should be able to point to the red ball but may not be able to verbally express her comprehension of the doctor's command.
Typically receptive aphasia is caused by damage to the left hemisphere of the brain. The most common cause of this damage is a stroke, or insufficient oxygen supply to the brain. However, aphasia can also be caused by an infection of the brain, a brain tumour that is located near or within any of the language facilities or severe head trauma or injury.
Patients with less severe forms of receptive dysphasia are more likely to recover fully. Patients who contracted aphasia due to a head injury or external trauma are more likely to recover than patients who suffered the damage due to a stroke. Approximately one in three aphasics will recover fully within 3 months of his injury. If the patient has not recovered within 6 months of the injury or stroke, complete recovery is unlikely.
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