Aphasia is a disorder of language.
Broadly considered, there are four distinct types of aphasia: 1) Wernicke's Receptive Aphasia--which is a reduced ability to comprehend or perceive spoken words. 2) Broca's Expressive Aphasia--which is a reduced ability to speak beyond a few simple words. 3) Conduction Aphasia--which is due to a lesion which cuts the fiber passageways which link Wernicke's receptive auditory area with Broca's expressive speech area. Patients with conductive aphasia know what they want to say, but can't gain access to the words in order to speak them. 4) Global aphasia is an inability to speak or understand the sounds of language due to a massive left hemisphere lesion.
LANGUAGE & THE LEFT HEMISPHERE
Among 80-90% of right handers, and over 50-80% of those who are left handed, the left half of the brain is dominant for the perception and production of almost all aspects of non-emotional language, including reading, writing, speaking, spelling, naming, and the comprehension of the grammatical, syntactical, and descriptive components of language, including time sense, rhythm, musical scales, verbal concept formation, analytical reasoning, and verbal memory.
As demonstrated with functional imaging and blood flow studies, when reading, speaking, and naming, the left hemisphere becomes highly active. Likewise, when playing musical scales, or listening to the rhythmical aspects of music, the left temporal lobe increases in activity (Evers et al., 1999; Parsons & Fox, 1997).
As demonstrated through lesion studies, functional imaging, and dichotic listening, the human left hemisphere adominates in the perception and processing of real words, word lists, rhymes, numbers, backwards speech, morse code, consonants, consonant vowell syllables, nonsense syllables, the transitional elements of speech, and single phonemes. It is also dominant for recognizing phonetic, conceptual, and verbal (but not physical) similarities; for example, determining if two letters (g & p vs g & q) have the same vowel ending.
However, the left hemisphere is not only dominant for language, but specific regions within the left hemisphere are responsible for the ability to comprehend vs speak the sounds of language.
PURE WORD DEAFNESS
The the primary auditory receiving areas are located within the right and left superior temporal lobes. If these areas are destroyed bilaterally, such as due to a bilateral stroke, the individual becomes cortically deaf. Although able to hear they cannot perceive or comprehend non-verbal sounds or understand spoken lanugage.
When the primary auditory area is destroyed, the auditory association areas (Wernicke's area in the left hemisphere) are disconnected from all sources of auditory input and thus cannot extract meaning from the auditory environment. When individuals are unable to perceive and identify linguistic and non-lingusitic sounds the deficit is described as a global or generalized auditory agnosia (Schnider et al. 1994). Cerebrovascular disease is the most common cause of this abnormality.
These patients are not deaf, however, as this can be ruled out by testing pure-tone threadholds. In fact, even with complete bilateral destruction of the primary auditory cortex there is no permanant loss of acoustic sensitivity (Rubens, 1993). This is because sounds continue to be received in thalamic and subcortical centers including the amygdala. Hence, patients can still detect sounds. However, they are unable to identify them and cannot recognize the sounds of speech, including spoken language.
Nevertheless, these patients can still speak. Unfortunately, they are unable to perceive the words they are saying as that information can no longer be received within the neocortex and cannot be transferred to Wernicke's area which is responsible for comprehending the sounds of speech.
Wernicke's area is located within the left superior temporal lobe and extends from the border zones of the primary auditory reception area toward the inferior parietal lobule.
Wernickes area (in conjunction and with the aid of the inferior parietal lobule; Kimura, 1993) acts to decode the sounds of language so that spoken as well as written words and sentences can be understood and comprehended.
For example, Wernicke's area provides the auditory equivalent of a visually perceived written word so that we know what the words we read sound like.
Wernicke's area is also referred to as the "auditory receiving area." If the auditory association (Wernicke's) area is damaged patients will have great difficulty comprehending spoken or written language. Naming, reading, writing and the ability to repeat or understand what is said are severely effected.
Frequently disturbances involving linguistic comprehension are due to an impaired capacity to discern the individual units of speech and their temporal order. This is because the sounds and speech must be separated into discrete interrelated linear units or they will be perceived as a blur, or even as a foreign language (Carmon & Nachshon, 1975; Efron, 1963; Joseph, 1982, 1988a; Lackner & Teuber, 1973). Hence, a patient with Wernicke's aphasia may perceive a spoken sentence such as the "big black dog" as "the klabgigdod". However, comprehension is improved if the spoken words are separated by long intervals.
Many receptive aphasics can comprehend frequently used words but have difficulty with those less frequently heard. Thus loss of comprehension is not an all-or-none phonemeonon. They will usually have the most difficulty understanding relational or syntactial structures, including the use of verb tense, possessives, and prepositions. However, by speaking slowly and by emphasizing the pauses between each individual word, comprehension can be modestly improved. Fluent Aphasia.
Patients with damage to Wernicke's area are still capable of talking (due to preservation of Broca's area). However, because Wernicke's area also acts to code linguistic stimuli for expression (prior to its transmission to Broca's area), expressive speech becomes severely abnormal, lacking in content, containing neologistic distortions (e.g. "the razgabin"), and/or characterized by non-sequitars, literal (sound substitution) and verbal paraphasic (word substitution) errors, a paucity of nouns and verbs, and the ommission of pauses and sentence endings (Christman, 1994; Goodglass & Kaplan, 1982; Kertesz, 1983a; Hecaen & Albert, 1978). Patients may speak in a rush (e.g. press of speech) and what is said often convey very little actual information; a condition referred to as fluent aphasia. They also may have difficulty establishing the boundaries of phonetic (confusing "love" for "glove") and semantic (cigarrette for ashtray) auditory information.
The speech of these patients may also be characterized by long, seemingly complex (albeit unintelligible) grammatically correct sentences, such that speech is often hyperfluent and produced at an excessive rate. They thus have difficulty bringing sentences to a close and many words are unitelligibly strung together. They also suffer severe word finding difficulty which adds a circumlocutory aspect to their speech which can deteriorate into jargon aphasia such that no meaningful communication can be made. (Christman 1994; Kertesz, 1983a; Marcie & Hecaen, 1979).
For example, one patient with severe receptive aphasia responded in the following manner: "....Oh hear but that was a long time ago that was when that when before I even knew that much about this place although I am a little suspicious about what the hell is the part there is one part scares, uh estate spares, Ok that has a bunch of drives in it and a bunch of good googin, nothing real big but that was in the same time I coached them I said hey stay out of the spear struggle stay out of trouble so dont get and my kidds, uh except for the body the boys are pretty good although lately they have become winded or something...what the hell...kind of a platz goasted klack..."
Presumably because the coding mechanisms involved in organizing what they are planning tosay are the same mechanisms which decode what they hear, expressive as well as receptive speech becomes equally disrupted. In fact, one gauge of comprehension can be based on the amount of normalcy in their language use. That is, if they can repeat only a few words normally, it is likely that they can only comprehend a few words as well. Nevertheless, in testing for comprehension it is important to insure that the patient's major difficulty is not apraxia or agnosia, rather than aphasia (to be discussed).
In addition, like speech the ability to write may be preserved, although what is written is usually completely unitelligible consisting ofjargon and neologistic distortions. Copying written material is possible although it is also often contaminated by errors.
Although the speech of a patient with Wernicke's aphasia sounds quite bizarre, these individuals generally do not realize that what they say is meaningless (Maher et al. 1994). Moreover, they may fail to comprehend that what they hear is meaningless as well (Lebrun, 1987). Nor can you tell them that they are speaking gobblygoop because they are unable to comprehend or understand what you are saying. When Wernickes area is damaged, there is no other region left to analyze the linguistic components of speech and language. The brain cannot be alerted to the patient's disability. They don't know that they don't know; that they don't understand. However, they may be somewhat more capable of recogning that their writing is abnormal (Marcie & Hecaen, 1979).
APHASIA & EMOTION
Patients with Wernicke's aphasia may display euphoria due to the disorganizing effect of comprehension loss on emotional functioning.
In some cases patients become paranoid as there remains a non-linguistic emotional awareness that something is not right; that what they hear and what they observe does not mesh or seem to coincide. Moreover, when they speak, others do not respond in the manner they are expecting--which makes them upset and sometimes paranoid.
However, although the left temporal lobe is injured, because the right hemisphere is intact, their ability to perceive and express social emotional nuances remains normal.
Since these paralingusitic and emotional features of language are analyzed by the intact right cerebral hemisphere, the aphasic individual is able to grasp in general the meaning or intent of a speaker, although verbal comprehension is reduced. This in turn enables them to react in a somewhat appropriate fashion when spoken to. Unfortunately, this also makes them appear to comprehend much more than they are capable of.
Because individuals with receptive aphasia display unusual speech, have lost comprehension, and failure to comprehend that they no longer comprehend or "make sense" when speaking, they are at risk for being misdiagnosed as psychotic or suffering from a formal thought disorder, i.e. "schizophenia". Indeed, individuals with abnormal left temporal lobe functioning sometime behave and speak in a "schizophrenic-like" manner (see Chapter 21). Given that they may also behave in a euphoric and/or paranoid manner only increases the likelihood of a misdiagnosis.
According to Benson (1993, p. 42), "those with Wernicke's aphasia often have no apparent physical or elementary neurological disability. Not infrequently, the individual who suddenly fails to comprehend spoken language and whose output is contaminated with jargon is diagnosed as psychotic. Patients with Wernicke's aphasia certainly inhabited some of the old lunatic asylums and probably are still being misplaced."
In fact, and as detailed in chapter 21, the left temporal lobe has been repeatedly implicated in schizophrenia as measured by positron-emission tomography (e.g. McGuire et al. 1998), P300 evoked potential amplitude (Bruder et al., 1999; Salisbury et al. 1998) and MRI (Jacobsen et al. 1998; Shidhabuddin et al. 1998; Kwon et al., 1999).
Global aphasia is essentially a total aphasia due to massive left hemisphere damage involving the entire language axis, i.e. the frontal, parietal and temporal convexity. Comprehension is severely reduced as is the ability to speak, read, write, or repeat. Patients are usually but not always (Legatt, Rubin, Kaplan, Healton, & Brust, 1987), paralyzed on the right side due to damage extending into the motor areas of the frontal lobe.
Frequently this disturbance is secondary to cerebrovascular disease involving the middle cerebral artery. However, tumors and head injuries can also create this condition.
ISOLATION OF THE SPEECH AREA (Or Transcortical Aphasia)
Isolation of the speech area is a condition where the cortical border zones surrounding the language axis have been destroyed due to occlusion of the tiny terrtiary blood vessels which supplies these regions (Geschwind et al. 1968). That is, the Language Axis of the left hemisphere becomes completely disconnected from surrounding cortical tissue but remains (presumably) an intact functional unit. This is in contrast, to global aphasia in which the three major zones of language have been destroyed.
Nevertheless, like global aphasia, the rest of the cerebrum is unable to communicate with the language zones. As such, an individual is unable to verbally describe what they see, feel, touch, or desire. Moreover, because the Language Axis cannot communicate with the rest of the brain, linguistic comprehension is largely abolished.
That is, although communication between Wernicke's, Broca's and the inferior parietal lobule is maintained, associations from other brain regions cannot reach the speech center. Although able to talk, the patient has nothing to say. Moreover, although able to see and hear, the patient is unable to linguistically understand what they perceive. However, they are capable of generating automatic-like responses to well known phrases, prayers, or songs.
In an interesting case described by Geschwind, Quadfasel and Segarra, (1968), a 22 year old woman with massive destruction of cortical tissue due to gas asphyxiation was found to have a preserved Language Axis. It was noted once the patient regained "consciousness" that "she sang songs and repeated statements made by the physicians. However, she would follow no commands, resisted passive movements of her extremities, and would become markedly agitated and sometimes injured hospital personnel. In all other regards, however, she was completely without comprehension or the ability to communicate.
The patients spontaneous speech was limited to a few stereotyped phrases, such as "Hi daddy", "So can daddy", "mother", or "Dirty bastard". She never uttered a sentence of propositional speech over the nine years of observation. She never asked for anything and she never replied to questions and showed no evidence of having comprehended anything said to her. Occasionally, however, when the examiner said, 'ask me no questions', she would reply 'I'll tell you no lies,' or when told, 'close your eyes' she might say 'go to sleep.' When asked, "Is this a rose?" she might say, "roses are red, violets are blue, sugar is sweet and so are you.": To the word "Coffee" she sometimes said, "I love coffee, I love tea, I love the girls and the girls love me. An even more striking phenomenon was observed early in the patients illness. She wold sing along with songs or musical commercials sung over the radio or would recite prayers along with the priest during religious broadcasts. If a record of a familiar song was played the patient would sing along with it. If the records was stopped she would continue singing correctly both words and music for another few lines and then stop. If the examiner kept humming the tune the patient would continue singing the words to the end. New songs were played to her and it was found she could learn these as evidenced by her ability to sing a few lines correctly after the record had been stopped. Furthermore, she could sing two different sets of words to the same melody. For example, she could sing "Let me call you sweetheart" with the conventional words, but also learned the parody beginning with "Let me call you rummy". Her articulation of the sounds and her production of melody were correct although she might sometimes substitute the words "dirty bastard" for some of the syllables" (pp 343-346).
Nevertheless, although such patients are able to sing, curse, and even pray, it is not clear if these expressions are the product of right hemisphere activity or reflexive activation of the intact language zones (or both). I favor the former rather than the later explanations.
In some cases the isolation is only partial, involving either than anterior or posterior regions. In these instances the disorder is referred to as transcortical motor or transcortical sensory aphasia respectively (see Hecaen & Albert, 1978 for greater detail). Individuals with a partial transcortical aphasia have been reported able to read out loud, to write to dictation, and to repeat simple verbal statements. However, although repetition is somewhat preserved, spontaneous speech is severely limited. In sensory transcortical disturbances comprehension is largely lost, whereas with motor transcortical there is a greater preservation of comprehension.
THE LANGUAGE AXIS & CONDUCTION APHASIA
Wernicke's area, in conjunction with the inferior parietal lobule (IPL, transmits to Broca's expressive speech area which articulates and expresses the sounds of speech.
Broca's expressive speech area is located along the outer surface of the left frontal lobe, adjacent to the secondary and primary motor area that represents the lips, mouth, jaw, and tongue. Upon receiving linguistic impulses from Wernicke's area (and the IPL), Broca's area acts to program the primary motor areas and the oral-laryngeal pathways in order to produce fluent and grammatical speech. However, as noted, if Wernicke's area were damaged, Broca's area (although uninjured) would instead spout nonsense words: "fluent aphasia." This is because Wernicke's area, in conjunction with the IPL, not only analyzes and organizes incoming but outgoing speech sounds, which are transmitted to Broca's area along a major fiber fundle, called the arcuate fasciculus.
Damage involving the arcuate fasciculus and/or the supramarginal gyrus of the left hemisphere can result in a condition referred to as conduction aphasia (Benson et al. 1973; Geschwind, 1965). Broca's area is essentially disconnected from the inferior parietal lobule and Wernicke's area, and although comprehension is intact, the patient cannot repeat words or read out loud. In these cases the lesion may extend to the insula and auditory cortex and underlying white matter of the left temporal lob, thereby distroying the axonal fibers of passage.
Individuals with this disorder have great difficulty communicating because a lesion in this vicinity disconnects Broca's area from the posterior language zones. Although a patient would know what he wanted to say, he would be unable to say it. Nor would he be able to repeat simple statements, read out loud, or write to dictation, although the ability to comprehend speech and written language would remain intact.
Nevertheless, these individuals are still able to talk. Unfortunately, most of what they say is contaminated by fluent paraphasic errors, phonetic word substitutions and the telescoping of words due to impaired sequencing. Patients also tend to confuse words which are phonetically similar. Because they can comprehend they are aware of their disturbances and will try to come up with the correct words via the generation of successive approximations (Marcie & Hecaen, 1979). Hence, speech may be circumlocutious, seemingly tangential, as well as contaminated by paraphasic distortions. Sentences are usually short and are often unrelated to each other (Marcie & Hecaen, 1979).
When writing, grapheme formation is usually normal. However, because they produce the wrong words and/or misspell what they produce, patients may frequently cross out words and perform overwriting (i.e. writing over various letters with additional strokes). Patients are frequently very frustrated, irritable, and upset regarding their condition.
Broca's area is located within the left frontal convexity and is responsible for the expression of speech. Immediately adjacent to Broca's area is the portion of the primary motor area which subserves control over the oral-facial musculature and the right hand.
As noted, linguistic information is transferred from the posterior portion of the Language Axis (via an axonal fiber bundle, the arcuate fasciculus) and converge upon Broca's area where they receive their final sequential (syntactical, grammatical) inprint so as to become organized and expressed as temporally ordered motoric linguistic articulations, i.e. speech. These impulses are then transferred to the adjacent frontal motor areas which in turn control the oral musculature. Hence, verbal communication and the expression of thought in linguistic form is made possible.
In consequence, damage to Broca's area results in expressive aphasia, and the patient is able to speak only a few well learned and emotional words. They may also retain the ability to swear and sing the words they can no longer say; singing, swearing, and the production emotional words being a function of the right frontal-temporal emotional-melodic speech areas. Thus, in mild cases of Broca's aphasia, emotional, melodic, and prosodic sound production may remain somewhat normal; that is, unless the lesion is deep and encroaches on the cingulate gyrus in which case prosody becomes decidedly abnormal. With deep frontal lesions or if the cingulate is negatively impacted, patients may sound as if they are speaking with a foreign accent.
Often immediately following a massive stroke in the left frontal region patients will suffer a paralysis of the right upper extremity and initially are almost completely unable to speak. Comprehension, however, is generally intact.
In severe cases speech may be restricted to a few stereotyped phrases and expressions, such as "Jesus Christ" or to single words such as "Fine", "yes", "No", which are produced with much effort. Even if capable of making longer statments, much of what they say is poorly articulated and/or mumbled such that only a word or two may be intelligible. However, this allows them to make one word answers in response to questions. Nevertheless, speech is almost always aggrammatical (i.e. the production of some correct words but in the wrong order), contaminated by verbal paraphasias, i.e. "orrible" for "auto", and/or the substitution of sematically related words, e.g. mother for father and characterized by the ommission of relational words such as those which tie language together, i.e. the propositions, modifiers, articles and conjunctions.
Similarly, they sometimes have difficulty comprehending these same grammatical features. Their ability to repeat what is said to them, although grossly deficient, is usually not as severly reduced as is conversational speech.
The ability to write is always effected with left frontal lesions and among patients with Broca's aphasia. Similarly, their capacity to write to dictation is severely limited. However, the ability to copy is much better preserved. In addition reading comprehension is usually intact although they cannot read aloud.
Sex Differences in Expressive Aphasia.
Broca's speech area appears to be more functionally developed in women than men. That is, there is some evidence which suggests that expressive (and emotional) speech tends to be more clearly concentrated in the anterior regions of the female brain (Kimura, 1993) In consequence, females are far more likely to become severely aphasic with left frontal injuries, whereas males become more severely aphasic with left parietal damage (Hier et al. 1994; Kimura, 1993).
DEPRESSION & BROCA'S APHASIA
Individuals with left frontal damage and Broca's aphasia often become frustrated, sad, tearful and depressed. This is because individuals with Broca's aphasia are able to comprehend and are well aware of their deficit and become appropriately depressed. Indeed those with the smallest lesions become the most depressed --the depression as well as the ability to sing being mediated, presumably by the intact right cerebral hemisphere.
It has also been reported that psychiatric patients classified as depressed (who presumably have no signs of neurological impairment) often demonstrate, electrophysiologically, insufficient activation of the left frontal lobe (d'Elia & Perris, 1973; Perris, 1974). With recovery from depression left hemisphere activation returns to normal levels.
Functional imaging of depressed states also indicates reduced activity in the left frontal lobe and anterior cingulate (Bench, et al., 1992). And when patients ceased to be depressed, activity levels increase (Bench et al., 1995).
Depression and depressive-like features also occur with left frontal and medial lesions which spare Broca's area (Robinson et al. 1984; Robinson and Szetela 1981; Sinyour, et al. 1986). However, rather than depression per se (particularly when the frontal pole is damaged), these patients frequently appear severely apathetic, blunted, hypoactive with reduced motor functioning, and are poorly motivated. Of course they may also be depressed.
Even so, when questioned, rather than worried or truly concerned about their condition the overall picture may be one of bland confusion, disinterest and emotionally blunting and related disturbances suggestive of a blunted form of schizophrenia.
Presumably, these depressed, blunted, and apathetic states are sometimes due to disconnection from the limbic system and/or right cerebral hemisphere. Unfortunately, with frontal pole injury, tumor or degeneration the underlying neurological precursors to their condition are not very apparent until late in the disease. Hence, misdiagnosis is likely. That is, patients may be misdiagnosed as depressed when in fact they have suffered a lesion, stroke, or abnormal growth in the left frontla lobe.
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