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

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.