Ganong's Review of Medical Physiology, 23rd Edition

sylvian fissure (lateral cerebral sulcus) of the categorical hemisphere.
A region at the posterior end of the superior temporal
gyrus called Wernicke’s area (Figure 19–7) is concerned with
comprehension of auditory and visual information. It projects
via the arcuate fasciculus to Broca’s area (area 44) in the
frontal lobe immediately in front of the inferior end of the motor
cortex. Broca’s area processes the information received
from Wernicke’s area into a detailed and coordinated pattern
for vocalization and then projects the pattern via a speech articulation
area in the insula to the motor cortex, which initiates
the appropriate movements of the lips, tongue, and
larynx to produce speech. The probable sequence of events
that occurs when a subject names a visual object is shown in
Figure 19–8. The angular gyrus behind Wernicke’s area appears
to process information from words that are read in such
a way that they can be converted into the auditory forms of the
words in Wernicke’s area.
It is interesting that in individuals who learn a second language
in adulthood, fMRI reveals that the portion of Broca’s
area concerned with it is adjacent to but separate from the
area concerned with the native language. However, in children
who learn two languages early in life, only a single area
is involved with both. It is well known, of course, that children
acquire fluency in a second language more easily than
adults.
LANGUAGE DISORDERS
Aphasias are abnormalities of language functions that are not
due to defects of vision or hearing or to motor paralysis. They
are caused by lesions in the categorical hemisphere (see Clinical
Box 19–2). The most common cause is embolism or thrombosis
of a cerebral blood vessel. Many different classifications of the
aphasias have been published, but a convenient classification
divides them into fluent, nonfluent, and anomic aphasias. In
nonfluent aphasia, the lesion is in Broca’s area (Table 19–1).
Speech is slow, and words are hard to come by. Patients with severe
damage to this area are limited to two or three words with
which to express the whole range of meaning and emotion.
Broca’s
area
Arcuate
fasciculus
Angular gyrus
Wernicke’s area
FIGURE 19–7 Location of some of the areas in the categorical
hemisphere that are concerned with language functions.
CHAPTER 19 Learning, Memory, Language, & Speech 297
Broca’s area
Facial area of
motor cortex
(area 4)
Wernicke’s
area
(area 22)
Angular gyrus
(area 39)
Higher order visual
cortical areas
(area 18)
FIGURE 19–8 Path taken by impulses when a subject names a
visual object projected on a horizontal section of the human brain.
Sometimes the words retained are those that were being spoken
at the time of the injury or vascular accident that caused the
aphasia.
In one form of fluent aphasia, the lesion is in Wernicke’s
area. In this condition, speech itself is normal and sometimes
the patients talk excessively. However, what they say is full of
jargon and neologisms that make little sense. The patient also
fails to comprehend the meaning of spoken or written words,
so other aspects of the use of language are compromised.
Another form of fluent aphasia is a condition in which
patients can speak relatively well and have good auditory
comprehension but cannot put parts of words together or
conjure up words. This is called conduction aphasia because
it was thought to be due to lesions of the arcuate fasciculus
connecting Wernicke’s and Broca’s areas. However, it now
TABLE 19–1 Aphasias. Characteristic
responses of patients with lesions in various
areas when shown a picture of a chair.
Type of Aphasia and Site of Lesion
Nonfluent (Broca’s area) “Tssair”
Characteristic
Naming Errors
Fluent (Wernicke’s area) “Stool” or “choss” (neologism)
Fluent (areas 40, 41, and 42; conduction
aphasia)
6
4
Arcuate
fasciculus
5
From lateral
geniculate nucleus
1
3 2
Left Right
Primary visual cortex
(area 17)
“Flair . . . no, swair . . . tair.”
Anomic (angular gyrus) “I know what it is . . . I have a
lot of them.”
Modified from Goodglass H: Disorders of naming following brain injury. Am Sci
1980;68:647.