Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 2) pptx

Aphasia, Memory Loss, and Other Focal Cerebral Disorders Part 2 THE LEFT PERISYLVIAN NETWORK FOR LANGUAGE: APHASIAS AND RELATED CONDITIONS Language allows the communication and elabora

Chapter 027 Aphasia, Memory Loss, and Other Focal Cerebral Disorders

(Part 2)

THE LEFT PERISYLVIAN NETWORK FOR LANGUAGE: APHASIAS AND RELATED CONDITIONS

Language allows the communication and elaboration of thoughts and experiences by linking them to arbitrary symbols known as words The neural substrate of language is composed of a distributed network centered in the

perisylvian region of the left hemisphere

The posterior pole of this network is located at the temporoparietal

junction and includes a region known as Wernicke's area An essential function of

Wernicke's area is to transform sensory inputs into their lexical representations so that these can establish the distributed associations that give the word its meaning

The anterior pole of the language network is located in the inferior frontal

gyrus and includes a region known as Broca's area An essential function of this

area is to transform lexical representations into their articulatory sequences so that the words can be uttered in the form of spoken language The sequencing function

of Broca's area also appears to involve the ordering of words into sentences that

contain a meaning-appropriate syntax (grammar)

Wernicke's and Broca's areas are interconnected with each other and with additional perisylvian, temporal, prefrontal, and posterior parietal regions, making

up a neural network subserving the various aspects of language function Damage

to any one of these components or to their interconnections can give rise to

language disturbances (aphasia) Aphasia should be diagnosed only when there

are deficits in the formal aspects of language such as naming, word choice, comprehension, spelling, and syntax

Dysarthria and mutism do not, by themselves, lead to a diagnosis of aphasia The language network shows a left hemisphere dominance pattern in the vast majority of the population In ~90% of right handers and 60% of left handers, aphasia occurs only after lesions of the left hemisphere In some individuals no hemispheric dominance for language can be discerned, and in some others (including a small minority of right handers) there is a right hemisphere dominance for language A language disturbance occurring after a right

hemisphere lesion in a right hander is called crossed aphasia

Clinical Examination

The clinical examination of language should include the assessment of naming, spontaneous speech, comprehension, repetition, reading, and writing A

deficit of naming (anomia) is the single most common finding in aphasic patients

When asked to name common objects (pencil or wristwatch), the patient may fail

to come up with the appropriate word, may provide a circumlocutious description

of the object ("the thing for writing"), or may come up with the wrong word

(paraphasia) If the patient offers an incorrect but legitimate word ("pen" for

"pencil"), the naming error is known as a semantic paraphasia; if the word

approximates the correct answer but is phonetically inaccurate ("plentil" for

"pencil"), it is known as a phonemic paraphasia Asking the patient to name body

parts, geometric shapes, and component parts of objects (lapel of coat, cap of pen) can elicit mild forms of anomia in patients who can otherwise name common objects In most anomias, the patient cannot retrieve the appropriate name when shown an object but can point to the appropriate object when the name is provided

by the examiner This is known as a one-way (or retrieval-based) naming deficit

A two-way naming deficit exists if the patient can neither provide nor recognize the correct name, indicating the presence of a language comprehension

impairment Spontaneous speech is described as "fluent" if it maintains

appropriate output volume, phrase length, and melody or as "nonfluent" if it is sparse, halting, and average utterance length is below four words The examiner

should also note if the speech is paraphasic or circumlocutious; if it shows a relative paucity of substantive nouns and action verbs versus function words (prepositions, conjunctions); and if word order, tenses, suffixes, prefixes, plurals,

and possessives are appropriate Comprehension can be tested by assessing the

patient's ability to follow conversation, by asking yes-no questions ("Can a dog fly?", "Does it snow in summer?") or asking the patient to point to appropriate objects ("Where is the source of illumination in this room?") Statements with embedded clauses or passive voice construction ("If a tiger is eaten by a lion, which animal stays alive?") help to assess the ability to comprehend complex syntactic structure Commands to close or open the eyes, stand up, sit down, or roll over should not be used to assess overall comprehension since appropriate responses aimed at such axial movements can be preserved in patients who otherwise have profound comprehension deficits

Repetition is assessed by asking the patient to repeat single words, short

sentences, or strings of words such as "No ifs, ands, or buts." The testing of repetition with tongue-twisters such as "hippopotamus" or "Irish constabulary" provides a better assessment of dysarthria and palilalia than aphasia Aphasic patients may have little difficulty with tongue-twisters but have a particularly hard time repeating a string of function words It is important to make sure that the number of words does not exceed the patient's attention span Otherwise, the failure of repetition becomes a reflection of the narrowed attention span rather

than an indication of an aphasic deficit Reading should be assessed for deficits in reading aloud as well as comprehension Writing is assessed for spelling errors, word order, and grammar Alexia describes an inability to either read aloud or comprehend single words and simple sentences; agraphia (or dysgraphia) is used

to describe an acquired deficit in the spelling or grammar of written language