sections include: mechanisms of aphasia, mechanisms of dysarthria, diagnosis and treatment
To have trouble communicating can be one of the most frustrating neurological symptoms a person may suffer. Such difficulty threatens our ability to express our needs, desires, and thoughts and to maintain relationships with the people we love. Problems with speech and language arise in many disorders, affecting people in different degrees.
Language being a complex function, there are many ways a person can develop a problem speaking, so it is useful to break down the process. By language, we refer to the way we use symbols, spoken or written, to communicate. There are many languages (English, Spanish, Chinese, and so on) and many types of language (spoken, written, and signed, plus musical notation, mathematical symbols, and other specialized forms). But most language processing and disorders that impair it are all similarly situated in the brain. Speech refers to the mechanics of how we usually produce language: controlling our breathing, voice box, tongue, and lips to form sounds. We can further divide that communication into four steps:
- semantics—the meaning
- syntax—the organization of words into sentences
- phonology—the mechanical and sound aspects of spoken language
- pragmatics—the social aspects of conversation, such as taking turns
Each of these stages can be disturbed by brain disorders and neuropsychiatric diseases that prevent someone from carrying on a normal conversation.
The term aphasia refers to the disruption of a person’s ability to communicate with language after developing a brain disease. Dysarthria refers to abnormalities in articulating that disturb a person’s speech as a result of impairment of the motor function.
Mechanisms of Aphasia
Language is mediated primarily by the left hemisphere of the brain. The rear part is responsible for processing the meaning of language (semantics), and the front part for the syntactical elements of speech (grammar, arrangements of words into sentences, and so on).
The most common cause of aphasia is a stroke (ischemic, hemorrhagic). Strokes involving the rear, or posterior, part of the brain where language meaning is handled thus produce a “fluent aphasia,” characterized by many words strung together in long sentences but communicating little meaning. Strokes involving the front part of the brain produce a “nonfluent aphasia,” in which a person tends to give short, grammatically simple replies. Patients with fluent aphasia (posterior) typically have difficulty understanding other people’s language, whereas patients with nonfluent aphasia can often understand what they hear. If a large stroke involves both the posterior and anterior parts of the left hemisphere, however, the person will have both nonfluent output and difficulty understanding others. When aphasia is due to a single brain lesion such as a stroke, the person generally knows what he or she wants to say but has difficulty formulating the words (nonfluent aphasia) or formulates them incorrectly (fluent aphasia). In general, large brain injuries produce more severe aphasia from which it is more difficult to recover. Brain imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) demonstrates the lesion and shows its size.
Risk factors for strokes include hypertension, obesity, cigarette smoking, and high levels of blood cholesterol or fat. Controlling your blood pressure, diet, and weight and not smoking will therefore reduce your likelihood of ever developing aphasia. It is much easier to avoid a stroke than to try to recover from one.
Alzheimer’s disease also commonly produces aphasia. The aphasia of Alzheimer’s disease is of the fluent type. In most cases, it is mild in the early stages of the disease and progresses slowly as the illness worsens. In a few cases, aphasia is very severe. Do not assume, however, that any difficulty remembering words or otherwise using language is a sign of incipient Alzheimer’s. Such events are normal as we age.
Brain injury in automobile accidents or other types of trauma and brain cancers can produce aphasia if they affect particular parts of the left side of the brain. In rare cases, such brain infections as encephalitis cause the problem as well.
Aphasia is commonly accompanied by alexia (difficulty reading) and agraphia (difficulty writing). The features of the alexia are similar to those of the aphasia (fluent or nonfluent) because speaking and reading depend on the same basic language regions of the brain. Alexia occurs more often with lesions in the back part of the left hemisphere than in the front part. Some children with dyslexia have had brain injury at a young age, producing an aphasic syndrome. In most cases, however, dyslexia is a developmental disorder involving reading and writing only.
Mechanisms of Dysarthria
Dysarthrias can be produced by any disturbance of the complex motor apparatus we use to produce sounds: the tongue, lips, vocal cords, and muscles that push air out through our mouths. We can see a temporary form of this difficulty in intoxicated individuals; their speech is slurred because they cannot coordinate their lip and tongue movements. Strokes and tumors that affect the parts of the brain responsible for motor function can produce a more long-lasting dysarthria, as can amyotrophic lateral sclerosis and similar motor neuron disorders. Such brain diseases as Parkinson’s reduce voice volume, leading to soft-spoken speech. People with dysarthria are usually able to understand language well and can sometimes communicate by other means.
Naturally, people who express themselves through sign language develop the equivalent of dysarthrias if they cannot use their hands to form words. This condition might arise due to strokes, peripheral neuropathy, apraxias and other muscle disorders. Signers can also experience aphasia in sign if they sustain injury to the language-related areas of the left hemisphere.
Brain trauma and cancers can produce dysarthria or other conditions that interfere with communication if they affect the movement and coordination regions of the brain. Usually a person with these conditions experiences other symptoms as well.
Diagnosis and Treatment
Someone having a stroke often notices paralysis of an arm and leg on the same side, or difficulties with vision. Because language is mediated by the left hemisphere of the brain, which controls the right side of the body, the onset of aphasia is frequently accompanied by paralysis of the right arm or leg or both. Any possible stroke is an emergency, and the person must be taken to a hospital immediately. There, doctors will diagnose the type of stroke with a brain scan and may administer clot-dissolving chemicals, blood-thinning agents, or other treatments.
A short-lived aphasia, especially in conjunction with right-sided weakness, may be due to a transient ischemic attack (TIA), which temporarily reduces the flow of blood to part of the brain. This, too, is a medical emergency. It is also a warning of the possibility of serious strokes unless one takes preventive steps.
Speech therapists often help people who have aphasia after a stroke recover as much of their language function as possible through the optimal use of uninjured brain areas. Fluent and nonfluent aphasia respond to different therapeutic approaches; music and singing often helps a person with nonfluent aphasia speak more freely. Speech therapy maximizes the recovery of injured brain regions and recruits brain areas not typically devoted to language. The prognosis for recovering language after a stroke varies. People with severe aphasia tend to have limited recovery, but those with a mild condition have a better prognosis. Most people exhibit some degree of spontaneous recovery, and speech therapy may help them regain more linguistic skills. Most of the restoration likely to occur is evident within six months of the stroke, and it is nearly complete within two years. After that, if they have not regained speech, people may be able to gesture in order to communicate simple needs but will never return to their previous language skills. Medications are typically of little use.
When an older person slowly develops aphasia along with abnormalities of memory, it is frequently a sign of a degenerative brain disease such as Alzheimer’s. Individuals experiencing such a condition should be assessed by a neurologist. There are treatments that can help improve the symptoms of Alzheimer’s disease or slow the loss of function, though there is no cure.
If aphasia is due to Alzheimer’s disease, then treatment will be directed at the underlying illness. Speech therapy is usually of little value for people with this disorder because Alzheimer’s is progressive, meaning the aphasia and other symptoms will get worse.
Speech therapy may be useful in reducing some aspects of dysarthria. Therapists can teach people how to articulate best with the abilities they still have and help them and their families develop alternate means of communication that work well.
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