What are aphasias?
Nearly all definitions of aphasia agree on the following four points: aphasia refers to a condition in which a person suffers a loss in the ability to understand or produce language-based material; the deficits can be in speech, reading, or writing; the impairment is assumed to be caused by cerebral rather than peripheral impairments; and aphasias represent a devastation of a previously manifested ability rather than a developmental failure.
A fifth point, included or implied in most descriptions of aphasias, is that they occur as a result of structural damage or disease processes that directly affect the brain—an organic etiology. This view is taken because functional mental disorders, such as major depression, that produce aphasic-like symptoms are best understood in the context of the psychological and environmental events that produce them, while aphasias are best comprehended in relationship to the physical injuries and structural changes that cause them to manifest. Furthermore, interventions that would be effective for the treatment of aphasias would have little or no relevance for the amelioration of aphasic-like symptoms that result from functional causes.
Aphasia is most commonly associated with damage to the left hemisphere of the brain, which is where most people's language abilities are localized; damage to the right side of the brain seldom results in any noticeable effect on language skills. The fact that left-handed people sometimes show speech impairments following injury to the right side of the brain has often been taken as evidence that they are right-brain dominant in regard to language, but research has failed to support this contention. Most left-handed people show bilateral or left-hemisphere dominance for language, with no more than 15 percent showing primary control of speech via the right hemisphere.
Anyone can acquire aphasia, but most people who have this disorder are in their middle to late years. Men and women are equally affected, and there are no apparent ethnic differences in the prevalence of aphasia. Vascular disorders, particularly strokes, are the most frequent cause of aphasia; other conditions likely to lead to aphasia include traumatic head injuries, brain tumors, infections, toxins, and dementia. In 2011, the National Aphasia Association estimated that approximately one million people in the United States had been diagnosed with aphasia, with over one hundred thousand new cases diagnosed each year.
Aphasias can be divided into three general categories: expressive aphasias, receptive aphasias, and mixed or global aphasias. Most persons with aphasia show a mixture of expressive and receptive symptoms.
Expressive aphasia is often referred to as Broca’s aphasia, motor aphasia, nonfluent aphasia, executive aphasia, or verbal aphasia. It describes a condition in which language comprehension remains intact but speech, and quite often the ability to write, is impaired. People who suffer from expressive aphasia understand what is being asked of them, and their ability to read is unaffected, but they have difficulty communicating their understanding. Expressive aphasia can be considered to subsume subfluent aphasia, anarthric aphasia, expressive dysprosody, kinetic (efferent) motor aphasia, speech apraxia, subcortical motor aphasia (pure word dumbness), transcortical motor aphasia (dynamic aphasia), conduction (central) aphasia, anomic (amnestic or nominal) aphasia, and agraphia, or the inability to write.
Verbal fluency, the capacity to produce uninterrupted phrases and sentences, is typically adversely affected in expressive aphasias. As a result of word-finding difficulties, speech may become halting and labored. For example, a person with Broca’s aphasia may say “Walk dog” instead of “I will take the dog for a walk.” The same sentence could also mean “You take the dog for a walk” or “The dog walked out of the yard,” depending on the circumstances. When expressive aphasia is extreme, the affected person may be totally unable to speak (aphonia) or may only be able to speak in so distorted a way that he or she becomes incomprehensible. Still, as is the case with all other forms of aphasia, the abilities to sing and swear are generally preserved.
Paraphasias are a common form of expressive aphasia. Paraphasia differs from articulation problems, which are also quite prominent. When people with expressive aphasia have difficulties with articulation, they have trouble making recognizable speech sounds; paraphasia, on the other hand, refers to a condition in which articulation is intact but unintended syllables, words, or phrases are inserted. For example, one patient, in referring to his wife, always said “my dog.”
Telegraphic speech, in which speech is reduced to its most elemental aspects, is frequently encountered in expressive aphasia. In telegraphic speech, the meaning is often clear, but communications are reduced to the bare minimum and consist of simple noun-verb phrases.
Receptive aphasia is often referred to as Wernicke’s aphasia, sensory aphasia, fluent aphasia, or agnosia. Receptive aphasia can be considered to subsume semantic aphasia, jargon aphasia, visual aphasia (pure word blindness), transcortical sensory aphasia (isolation syndrome), syntactical aphasia, and alexia. In receptive aphasia, speech is generally fluent, with few, if any, articulatory problems; however, deficits in language comprehension are always present.
Although fluent, the speech of a person with receptive aphasia is seldom normal. People who have receptive aphasia may insert nonwords, or neologisms, into their communications, and in severe cases their communications may contain nothing but jargon speech. For example, one patient, when asked what he had for breakfast, responded, “Eating and food. Got no more heavy come to there. No come good, very good, in morning.”
Unlike people who have expressive aphasia, who generally show great distress regarding their disorder, people with receptive aphasia may appear oblivious to their disorder. They may produce lengthy nonsensical utterances and then look at the listener as if confused by the listener’s lack of comprehension.
Global aphasia describes a condition in which there is a mixture of receptive and expressive deficits. Global aphasia is typically associated with less focalized brain injury. Although comprehension is generally less impaired than production in global aphasia, this disorder does not fit neatly into either the expressive or the receptive category. The prognosis is generally much poorer for persons with global aphasia than for those with purely receptive or expressive deficits.
Determining the nature and extent of an aphasia in an affected individual helps identify disease processes that may be affecting cerebral functioning, assists in the localization of brain injuries, and provides information that should be considered in making post-discharge placements. In addition, a thorough understanding of the nature and extent of symptoms in individual cases is extremely important, as aphasias cause significant communication deficits that require treatment.
There are a variety of conditions that can lead to aphasic-like symptoms: functional mental disorders, peripheral nervous system damage, peripheral motor impairments, congenital disorders, degenerative disease processes of the brain, cerebral vascular injury, central nervous system toxins, epilepsy, migraines, brain tumors, central nervous system infections, and cerebral trauma. Being able to discriminate between true aphasias caused by cerebral complications and aphasic-like symptoms brought on by other causes is necessary in order to provide the most effective treatment. For example, depression, Parkinson’s disease, and certain focal lesions can all cause a person to appear emotionally unreactive (flat affect) and speak in a manner that lacks expressive intensity and intonation (dysprosody). The treatments of choice for these disorders are substantially different, and some interventions that would be recommended for one disorder would be contraindicated for another. Similarly, knowing that cerebral hemorrhage is most often associated with global aphasia and diffuse tissue damage, whereas cerebral embolisms typically damage areas served by the left middle cerebral artery and result in more specific aphasias, can significantly affect patient monitoring, treatment, and prognosis.
The interrelationships between aphasias and localized brain injuries have important ramifications. Among other implications, knowing the neural basis for language production and processing can facilitate the identification of the best candidate sites for surgical intervention and provide clues regarding whether a disease process has been arrested or continues to spread. For example, an aphasia that begins with clear articulation and no identifiable deficits in language production would be consistent with conduction aphasia, and it might be assumed that damage to the arcuate fasciculus had occurred. If, over time, the person began to manifest increasing difficulty with speech comprehension but articulation continued to appear intact, it could be inferred that damage was spreading downward and affecting a broader region of the temporal lobe. Such information would have important ramifications for treatment and prognosis.
Given the importance of language and the ability to communicate in everyday life, the nature and the extent of a patient’s aphasia must be taken into account when making post-discharge plans. If the person’s deficits are purely expressive in nature, he or she is more likely to be able to manage his or her daily affairs, while a person with receptive aphasia may have to be referred to a more restrictive environment. Not being able to understand the communications of others can compromise safety and judgment, and a person with receptive aphasia should be carefully assessed to ascertain the degree to which he or she is competent to manage his or her affairs.
Aphasias cause significant communication problems that require treatment and amelioration. Although there is no doubt that many patients experience spontaneous recovery from aphasia, research shows that treatment can speed up the process. Furthermore, the earlier treatment is initiated, the more profound its effects.
Under most circumstances, therapy for aphasia is just one element of a more comprehensive treatment process. Aphasia seldom occurs in isolation, and, depending on the type of damage, one is likely to see paresis, memory deficits, apraxias, agnosias, and various difficulties related to information processing occurring in conjunction with the aphasia. As a result, the person with aphasia is likely to be treated by an interdisciplinary team, typically consisting of one or more physicians, nurses, nursing support personnel, physical therapists, occupational therapists, speech therapists, a rehabilitation psychologist or neuropsychologist, a clinical psychologist, and one or more social workers. Each team member is expected to have an area of expertise and specialization, but the team approach requires that team members work together and support each discipline’s treatment goals.
Common treatments for aphasia include systematic stimulation, behavioral teaching programs, deblocking, and compensation therapy. Systematic stimulation involves the use of everyday objects and situations to stimulate language production and facilitate language comprehension. Behavioral teaching programs are similar to systematic stimulation but are more organized, are designed more precisely to take into account known structural damage, and frequently employ behavior modification techniques. Deblocking, a less frequently used therapy, consists of stimulating intact language functions as a vehicle for encouraging rehabilitation of damaged processes. Compensation therapy includes teaching the person alternative communication strategies and how to use intact abilities to circumvent the functional limitations caused by aphasia.
Computers may also be used in aphasia treatment. One approach incorporates software that enables a computer to understand spoken language. Another approach uses a “processing prosthesis” that allows aphasic persons to construct computer-generated spoken sentences and store them for future use. Researchers exploring computer-based methods believe that these new methods will play complementary roles with existing aphasia therapies such as systematic stimulation.
One treatment option being explored is the possibility of using medication to prevent or reduce the severity of aphasia following a stroke. Strategies include the administration of drugs to restore compromised levels of neurotransmitters, to minimize the extent of cell loss in the brain, or to restore blood flow to regions of the brain that have become ischemic following a stroke.
The study of aphasias dates thousands of years. An Egyptian papyrus dated between 3000 and 2500 BCE provides a case example of language deficits following traumatic head injury. The Greeks variously subscribed to hypotheses that mental processes were located in the brain or the heart, and it was not until the time of second-century Roman physician Galen that the brain hypothesis gained full sway. Galen based his arguments on dissection and clinical experience; he had spent five years as a physician to the gladiators of the Roman circus, where he was exposed to multiple cases of traumatic head injury.
Over the next fourteen hundred years, little progress was made in terms of cerebral anatomy or physiology. With the anatomical observations of Andreas Vesalius and the philosophical speculations of René Descartes in the sixteenth century, however, the stage was set for a new understanding of cerebral functioning. In the early nineteenth century, phrenology, which postulated that specific areas of the brain controlled particular intellectual and psychological processes, became influential. Although it was subsequently discredited, phrenology provided the foundation for the localizationist position in neuropsychology.
Paul Broca can be credited with raising the study of cerebral localization of speech to a scientific level. Broca’s first case study was a patient nicknamed “Tan,” whose receptive abilities were apparently intact but whose expressive skills had been reduced to uttering the word “tan” and a few colorful oaths. According to Broca, Tan was shown in an autopsy to have a lesion of the left anterior lobe of his brain, which caused his speech problems. The syndrome subsequently became known as Broca’s aphasia, and the posterior third of the left third frontal convolution of the left hemisphere of the brain was named Broca’s area.
Carl Wernicke was the next person to make major contributions to the understanding of cerebral organization and language functioning. Wernicke proposed a sequential processing model in which several areas of the brain affected language development, production, and expression. Following his work, the left first temporal gyrus was named Wernicke’s area, and the particular type of receptive aphasia that results from damage to this area became known as Wernicke’s aphasia.
Over the ensuing years, arguments raged over whether the localizationist position was tenable. As a general rule, researchers supporting equipotentiality (sensory input may be localized, but perception involves the whole brain) held sway. By the 1950s, however, interactionist theory had gained the ascendancy. Interactionist theory holds that basic functions are localized, but there is redundancy in regard to function. Therefore, damage to a specific area of the brain may or may not cause a deficit in higher-order behaviors, since the damaged functions may be assumed by redundant or parallel backup components.
Recent years have seen notable advances in the understanding and treatment of aphasias. Psychometric instruments founded on modern principles of test construction have become available, and experimental techniques that take into account known aspects of cerebral functioning have been developed. Furthermore, advances in brain imaging, such as positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI), have done much to aid in understanding cortical function and the effects of injury as they relate to the development of aphasias. Functional magnetic imaging (fMRI) identifies areas in the brain that are used during activities such as speaking. This imaging technique may enable the field to address previously unanswerable questions, including what role the right hemisphere plays in recovery from aphasia, how individual differences in brain organization for language contribute to recovery from aphasia, and how rehabilitation for aphasia alters brain organization for language.
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