Global aphasia
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| 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]
Causes
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]
Diagnosis
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]