Global aphasia | |
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Global aphasia occurs due to a lesion in the perisylvian cortex, including Broca's and Wernike's areas. [1] |
Global aphasia is a severe form of nonfluent aphasia, caused by damage to the left side of the brain, that affects [1] receptive and expressive language skills (needed for both written and oral language) as well as auditory and visual comprehension. [2] Acquired impairments of communicative abilities are present across all language modalities, impacting language production, comprehension, and repetition. [3] [1] Patients with global aphasia may be able to verbalize a few short utterances and use non-word neologisms, [4] but their overall production ability is limited. [1] Their ability to repeat words, utterances, or phrases is also affected. [1] Due to the preservation of the right hemisphere, an individual with global aphasia may still be able to express themselves through facial expressions, gestures, and intonation. [3] [5] [6] This type of aphasia often results from a large lesion of the left perisylvian cortex. The lesion is caused by an occlusion of the left middle cerebral artery [4] [7] and is associated with damage to Broca's area, Wernicke's area, and insular regions which are associated with aspects of language. [8] [9]
It is most common for the onset of global aphasia to occur after a thrombotic stroke (at the trunk of the middle cerebral artery), with varying severity. [10] [11] The general signs and symptoms include the inability to understand, create, and repeat speech and language. [1] These difficulties also persist in reading, writing, and auditory comprehension abilities. [10] [12] Verbal language typically consists of a few recognizable utterances and words (e.g., hello), overlearned phrases (e.g., how are you), and expletives (e.g., a curse word). [2] However, those affected by global aphasia may express themselves using facial expressions, intonation, and gestures. [5] Extensive lexical (vocabulary) impairment is possible, resulting in an inability to read simple words or sentences. [13] [2] Global aphasia may be accompanied by weakness of the right side of the face and right hemiplegia (paralysis), [12] but can occur with or without hemiparesis (weakness). [14] Additionally, it is common for an individual with global aphasia to have one or more of the following additional impairments: apraxia of speech, alexia, pure word deafness, agraphia, facial apraxia, and depression. [11] [15]
Persons with global aphasia are socially appropriate, usually attentive, and task-oriented. [2] Some are able to respond to yes/no questions, but responses are more reliable when questions refer to family and personal experiences. [2] Automatic speech is preserved with normal phonemic, phonetic and inflectional structures. [12] Right hemiparesis or hemiplegia, right-sided sensory loss, and right homonymous hemianopsia may manifest as well. [16] Persons with global aphasia may recognize location names and common objects’ names (single-words), while rejecting pseudo-words and real but incorrect names. [17]
Global aphasia typically results from an occlusion to the trunk of the middle cerebral artery (MCA), [2] which affects a large portion of the perisylvian region of the left cortex. [7] Global aphasia is usually a result of a thrombotic stroke, which occurs when a blood clot forms in the brain's blood vessels. [16] [2] In addition to stroke, global aphasia can also be caused by traumatic brain injury (TBI), tumors, and progressive neurological disorders. [18] The large areas in the anterior (Broca's) and posterior (Wernicke's) area of the brain are either destroyed or impaired because they are separate branches of the MCA that are supplied by its arterial trunk. [16] Lesions usually result in extensive damage to the language areas of the left hemisphere, however global aphasia can result from damage to smaller, subcortical regions. [16] It is well known that a lesion to the cortex can cause aphasia. However, a study by Kumar et al. (1996) suggests that lesions to the subcortical regions of the cortex such as the thalamus, basal ganglia, internal capsule, and paraventricular white matter can also cause speech and language deficits. This is due to the fact that the subcortical regions are closely associated with the language centers in the brain. Kumar et al. state that while lesions to the subcortical regions could cause certain types of aphasia, a lesion to these regions would rarely cause global aphasia. [19] In a study performed by Ferro (1992), it was found that five different brain lesion locations were linked to aphasia. [20] These locations include: "fronto-temporo-parietal lesions", "anterior, suprasylvian, frontal lesions", "large subcortical infarcts", "posterior, suprasylvian, parietal infarcts", and "a double lesion composed of a frontal and a temporal infarct". [20]
If a suspected brain injury has occurred, the patient undergoes a series of medical imaging, which could include MRI (magnetic resonance imaging) or CT (computed tomography) scan. [21] After the diagnosis of a brain injury, a speech and language pathologist will perform a variety of tests to determine the classification of aphasia. [11] Additionally, the Boston Assessment of Severe Aphasia (BASA) is a commonly used assessment for diagnosing aphasia. [11] BASA is used to determine treatment plans after strokes lead to symptoms of aphasia and tests both gestural and verbal responses. [22] Cognitive functions can be assessed using the Cognitive Test Battery for Global Aphasia (CoBaGa). [23] The CoBaGa is an appropriate measure to assess a person with severe aphasia because it does not require verbal responses, rather manipulative answers. The CoBaGa assesses cognitive functions such as attention, executive functions, logical reasoning, memory, visual-auditory recognition, and visual-spatial ability. Van Mourik et al. conducted a study in which they assessed the cognitive abilities of people with global aphasia using the Global Aphasic Neuropsychological Battery. This test assesses attention/concentration, memory, intelligence, and visual and auditory nonverbal recognition. The results of this study helped the researchers determine there were varying levels of severity among individuals with global aphasia. [24]
Speech and language therapy is typically the primary treatment for individuals with aphasia. The goal of speech and language therapy is to increase the person’s communication abilities to a level functional for daily life. Goals are chosen based on collaboration between speech language pathologists, patients, and their family/caregivers. [25] Goals should be individualized based on the person’s aphasia symptoms and communicative needs. In 2016, Wallace et al. found the following outcomes were commonly prioritized in therapy: communication, life participation, physical and emotional well-being, normalcy, and health and support services. [26] However, available research is inconclusive about which specific approach to speech and language therapy is most effective in treating global aphasia.
Therapy can be either group or individual. Group therapies that integrate the use of visual aids allow for enhanced social and communication-skill development. [16] Group therapy sessions typically revolve around simple, preplanned activities or games, and aim to facilitate social communication. [16]
One particular therapy designed specifically for treatment of aphasia is Visual Action Therapy (VAT). [6] VAT is a non-verbal gestural output program with 3 phases and 30 total steps. [27] The program teaches unilateral gestures as symbolic representations of real life objects. Research on the effectiveness of VAT is limited and inconclusive. [27]
One important therapy technique includes teaching family members and caregivers strategies for more effectively communicating with their loved ones. Research offers such strategies including, simplifying sentences and using common words, gaining the person's attention before speaking, using pointing and visual cues, allowing for adequate response time, and creating a quiet environment free of distractions. [16]
Research supporting the efficacy of pharmacological treatments for aphasia is limited. To date, no large scale clinical trials have proven benefits of pharmacological treatment. [25]
When evaluating the prognosis of a patient, the main contributing participant factors that influence the extent of neuroplasticity, or the brain's ability to change are: age, lesion location, pre-existing cognitive status, motivation, overall health, and interaction amongst these. [28] After brain damage, initial signs of global aphasia may appear within the first two days due to brain swelling (cerebral edema). With some time and natural recovery, impairment presentation may progress into expressive aphasia (most commonly) or receptive aphasia. [2] [16] Due to the size and location of the lesion associated with global aphasia, the prognosis for language abilities is poor. [29] Research has shown that the prognosis of long-term language abilities is determined by the initial severity level of aphasia within the first four weeks after a stroke. [29] As a result, there is a poor prognosis for persons who retain a diagnosis of aphasia after one month due to limited initial language abilities. [2] [7] Nonetheless, in the first year post-stroke, patients with global aphasia showed improvement in their Western Aphasia Battery (WAB) scores from baseline. When compared to individuals with Broca’s, Wernicke’s, anomic, and conduction types of aphasia, those with Broca’s aphasia showed the best rate and extent of improvement followed by global aphasia. The rate of improvement in language function was highest in the first four weeks after stroke. [30]
Although the prognosis for persons diagnosed with global aphasia is poor, improvement in varying aspects of language is possible. For example, in 1992, Ferro performed research in which he studied the recovery of individuals with acute global aphasia, resulting from the five different lesion sites. [20] The first lesion site was in the fronto-tempo-parietal region of the brain; patients with lesions in this location saw the least amount of gains out of all of the participants in the study, and they often never recovered from global aphasia. [20] However, the second lesion site was the anterior, suprasylvian, frontal part of the brain; the third lesion site was the subcortical infarcts; and the fourth lesion site was the posterior, suprasylvian, parietal infarcts. [20] Participants with lesions two, three, and four often recovered to a less severe form of aphasia, such as Broca's or transcortical. [20] The fifth lesion site was a double lesion in both the frontal and temporal infarcts; patients with lesions at this site showed slight improvement. [20] However, studies show that spontaneous improvement, if it happens, occurs within six months, but complete recovery is rare. [31]
Studies have shown that persons with global aphasia have improved their verbal and nonverbal speech and language skills through speech and language therapy. [32] [33] One study examined the recovery of a group of individuals who were classified as having global aphasia at 3 months poststroke. The individuals received intensive speech and language intervention. The results of the study illustrated that all of the patients showed improvement. The greatest area of improvement was in auditory comprehension, and the least in the use of propositional speech. After 6 months poststroke, the individuals showed an increased use of gestures to communicate, as their communication skills remained severely impaired. [34]
During therapy, most progress is seen within the first 3 years, but it is possible for language abilities to continuously improve at a steady rate due to long-term intensive language intervention. [33] While improvement in language abilities is possible with intervention, only 20 percent of persons diagnosed with global aphasia achieve functional use of language. [2] Communication of basic needs and the comprehension of simple conversations on highly familiar topics, are examples of common functional language use for this population. [2]
In aphasia, a person may be unable to comprehend or unable to formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in the Global North. Aphasia can also be the result of brain tumors, epilepsy, autoimmune neurological diseases, brain infections, or neurodegenerative diseases.
Expressive aphasia, also known as Broca's aphasia, is a type of aphasia characterized by partial loss of the ability to produce language, although comprehension generally remains intact. A person with expressive aphasia will exhibit effortful speech. Speech generally includes important content words but leaves out function words that have more grammatical significance than physical meaning, such as prepositions and articles. This is known as "telegraphic speech". The person's intended message may still be understood, but their sentence will not be grammatically correct. In very severe forms of expressive aphasia, a person may only speak using single word utterances. Typically, comprehension is mildly to moderately impaired in expressive aphasia due to difficulty understanding complex grammar.
In neuroscience and psychology, the term language center refers collectively to the areas of the brain which serve a particular function for speech processing and production. Language is a core system that gives humans the capacity to solve difficult problems and provides them with a unique type of social interaction. Language allows individuals to attribute symbols to specific concepts, and utilize them through sentences and phrases that follow proper grammatical rules. Finally, speech is the mechanism by which language is orally expressed.
Wernicke's aphasia, also known as receptive aphasia, sensory aphasia, fluent aphasia, or posterior aphasia, is a type of aphasia in which individuals have difficulty understanding written and spoken language. Patients with Wernicke's aphasia demonstrate fluent speech, which is characterized by typical speech rate, intact syntactic abilities and effortless speech output. Writing often reflects speech in that it tends to lack content or meaning. In most cases, motor deficits do not occur in individuals with Wernicke's aphasia. Therefore, they may produce a large amount of speech without much meaning. Individuals with Wernicke's aphasia are typically unaware of their errors in speech and do not realize their speech may lack meaning. They typically remain unaware of even their most profound language deficits.
Broca's area, or the Broca area, is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production.
Aphasiology is the study of language impairment usually resulting from brain damage, due to neurovascular accident—hemorrhage, stroke—or associated with a variety of neurodegenerative diseases, including different types of dementia. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known: expressive aphasia and receptive aphasia.
Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating trauma-induced damage.
Anomic aphasia is a mild, fluent type of aphasia where individuals have word retrieval failures and cannot express the words they want to say. By contrast, anomia is a deficit of expressive language, and a symptom of all forms of aphasia, but patients whose primary deficit is word retrieval are diagnosed with anomic aphasia. Individuals with aphasia who display anomia can often describe an object in detail and maybe even use hand gestures to demonstrate how the object is used, but cannot find the appropriate word to name the object. Patients with anomic aphasia have relatively preserved speech fluency, repetition, comprehension, and grammatical speech.
The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's disease, it plays important roles in various other nonmotor functions as well, including procedural learning, associative learning and inhibitory control of action, among other functions. The caudate is also one of the brain structures which compose the reward system and functions as part of the cortico–basal ganglia–thalamic loop.
Wernicke's area, also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to Broca's area, which is primarily involved in the production of language. It is traditionally thought to reside in Brodmann area 22, which is located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 70% of left-handed individuals.
Conduction aphasia, also called associative aphasia, is an uncommon form of difficulty in speaking (aphasia). It is caused by damage to the parietal lobe of the brain. An acquired language disorder, it is characterised by intact auditory comprehension, coherent speech production, but poor speech repetition. Affected people are fully capable of understanding what they are hearing, but fail to encode phonological information for production. This deficit is load-sensitive as the person shows significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce. People have frequent errors during spontaneous speech, such as substituting or transposing sounds. They are also aware of their errors and will show significant difficulty correcting them.
Transcortical sensory aphasia (TSA) is a kind of aphasia that involves damage to specific areas of the temporal lobe of the brain, resulting in symptoms such as poor auditory comprehension, relatively intact repetition, and fluent speech with semantic paraphasias present. TSA is a fluent aphasia similar to Wernicke's aphasia, with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia").
Landau–Kleffner syndrome (LKS)—also called infantile acquired aphasia, acquired epileptic aphasia or aphasia with convulsive disorder—is a rare childhood neurological syndrome.
Transcortical motor aphasia (TMoA), also known as commissural dysphasia or white matter dysphasia, results from damage in the anterior superior frontal lobe of the language-dominant hemisphere. This damage is typically due to cerebrovascular accident (CVA). TMoA is generally characterized by reduced speech output, which is a result of dysfunction of the affected region of the brain. The left hemisphere is usually responsible for performing language functions, although left-handed individuals have been shown to perform language functions using either their left or right hemisphere depending on the individual. The anterior frontal lobes of the language-dominant hemisphere are essential for initiating and maintaining speech. Because of this, individuals with TMoA often present with difficulty in speech maintenance and initiation.
Mixed transcortical aphasia is the least common of the three transcortical aphasias. This type of aphasia can also be referred to as "Isolation Aphasia". This type of aphasia is a result of damage that isolates the language areas from other brain regions. Broca's, Wernicke's, and the arcuate fasiculus are left intact; however, they are isolated from other brain regions.
Auditory verbal agnosia (AVA), also known as pure word deafness, is the inability to comprehend speech. Individuals with this disorder lose the ability to understand language, repeat words, and write from dictation. Some patients with AVA describe hearing spoken language as meaningless noise, often as though the person speaking was doing so in a foreign language. However, spontaneous speaking, reading, and writing are preserved. The maintenance of the ability to process non-speech auditory information, including music, also remains relatively more intact than spoken language comprehension. Individuals who exhibit pure word deafness are also still able to recognize non-verbal sounds. The ability to interpret language via lip reading, hand gestures, and context clues is preserved as well. Sometimes, this agnosia is preceded by cortical deafness; however, this is not always the case. Researchers have documented that in most patients exhibiting auditory verbal agnosia, the discrimination of consonants is more difficult than that of vowels, but as with most neurological disorders, there is variation among patients.
Foix–Chavany–Marie syndrome (FCMS), also known as bilateral opercular syndrome, is a neuropathological disorder characterized by paralysis of the facial, tongue, pharynx, and masticatory muscles of the mouth that aid in chewing. The disorder is primarily caused by thrombotic and embolic strokes, which cause a deficiency of oxygen in the brain. As a result, bilateral lesions may form in the junctions between the frontal lobe and temporal lobe, the parietal lobe and cortical lobe, or the subcortical region of the brain. FCMS may also arise from defects existing at birth that may be inherited or nonhereditary. Symptoms of FCMS can be present in a person of any age and it is diagnosed using automatic-voluntary dissociation assessment, psycholinguistic testing, neuropsychological testing, and brain scanning. Treatment for FCMS depends on the onset, as well as on the severity of symptoms, and it involves a multidisciplinary approach.
Paraphasia is a type of language output error commonly associated with aphasia, and characterized by the production of unintended syllables, words, or phrases during the effort to speak. Paraphasic errors are most common in patients with fluent forms of aphasia, and come in three forms: phonemic or literal, neologistic, and verbal. Paraphasias can affect metrical information, segmental information, number of syllables, or both. Some paraphasias preserve the meter without segmentation, and some do the opposite. However, most paraphasias affect both partially.
Apraxia of speech (AOS), also called verbal apraxia, is a speech sound disorder affecting an individual's ability to translate conscious speech plans into motor plans, which results in limited and difficult speech ability. By the definition of apraxia, AOS affects volitional movement pattern. However, AOS usually also affects automatic speech.
Nina Dronkers is an American cognitive neuroscientist. She is known for her studies of aphasia and their application for understanding brain systems involved in normal language abilities. She is a professor in the Psychology Department at the University of California, Berkeley, and a faculty member of the Helen Wills Neuroscience Institute. She is also an Emerita Research Career Scientist of the Veterans Administration Northern California Health Care System where she established the Center for Aphasia and Related Disorders. She serves as a consultant for the Memory and Aging Center at UCSF Medical Center. In addition, she is an adjunct professor in the Department of Neurology, University of California, Davis, School of Medicine. She has published over 120 scientific papers and is the co-author with Lise Menn of a textbook: Psycholinguistics: Introduction and Applications, Second edition.
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