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Aphasia is defined as a disturbance of language processing caused by damage to the brain. It can be one of the most devastating consequences of structural or functional damage to the dominant hemisphere of the brain, that is, the hemisphere dominant for language. The left hemisphere is dominant for language in over 90% of all individuals—in virtually all persons who are right-handed, and in a majority of persons who are left-handed. Aphasia has long been recognized as a consequence of brain damage in the medical literature, and variants thereof were most clearly described by Broca and Wernicke in the 19th century. These were based on pathological studies and were the basis for the localization-based approach that has largely persisted to this day. During the 20th century, other variants of aphasia were identified and described, and in the dawning of the 21st century, a more systems-based approach has come into favor. This chapter will set out to accomplish the following:

  • Define terminology important for understanding language-based discussions.

  • Define basic neuroanatomic regions in the dominant (usually the left) hemisphere, which are important in primary language processing and output; and the corresponding regions in the nondominant (usually the right) hemisphere related to the processing and output of the emotional or nonverbal aspects of language.

  • Outline aphasic syndromes in their classic localization-based descriptions, as they remain essential to understand the “input and output” aspects of language, with the understanding that many different cortical–subcortical, and even inter-hemispheric, networks are activated in parallel, which allow for the comprehensive experience of “language.”

  • Discuss pitfalls and pearls in the evaluation of the patient with language deficits.

CASE 23-1

You are asked to see a 68-year-old man admitted into the ICU for sepsis. The patient presented initially with delirium and had somewhat incomprehensible speech. But as the delirium started clearing, the treating physician noted that the patient continued to have problems with speech or language. So, you were contacted for assessment. You ask what speech or language problem the patient might have.


First, it is important to understand the difference between a “speech” impairment and a “language” impairment. A deficit of speech is one that affects the articulatory and phonetic aspects of verbal expression. A language deficit is one which reflects an abnormality of the brain that causes impairments in the comprehension and/or generation of language.1 There are several terms that will be important to define before proceeding with any discussion of aphasia:1-3

  • Phoneme: smallest individual speech sounds

  • Morpheme: the joining of individual speech sounds, which become the units of words

  • Mutism: lack of any verbal output

  • Dysphonia: production of crude vowels only

  • Dysarthria: a problem of motor speech execution. Production of poorly articulated consonants, often with a slow pace, resulting in “slurring” of speech

  • Dyspraxia: altered motor planning of speech—faulty phrasing, ...

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