Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 19

Learning, Memory, Language, & Speech 297

sylvian fissure (lateral cerebral sulcus) of the categorical hemi-
sphere. 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 mo-
tor 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 ar-
ticulation area in the insula to the motor cortex, which ini-
tiates 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 ap-
pears 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 lan-
guage 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 chil-
dren who learn two languages early in life, only a single area
is involved with both. It is well known, of course, that chil-
dren 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 se-
vere damage to this area are limited to two or three words with
which to express the whole range of meaning and emotion.

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

FIGURE 19–7
Location of some of the areas in the categorical
hemisphere that are concerned with language functions.

Arcuate

fasciculus

Angular gyrus

Wernicke’s area

Broca’s

area

FIGURE 19–8

Path taken by impulses when a subject names a

visual object projected on a horizontal section of the human brain.

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

Characteristic

Naming Errors

Nonfluent (Broca’s area) “Tssair”

Fluent (Wernicke’s area) “Stool” or “choss” (neologism)

Fluent (areas 40, 41, and 42; conduc-

tion aphasia)

“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.

Wernicke’s

area

(area 22)

Angular gyrus

(area 39)

Higher order visual

cortical areas

(area 18) Primary visual cortex

(area 17)

From lateral

geniculate nucleus

Arcuate

fasciculus

Facial area of

motor cortex

(area 4)

Broca’s area

Left Right

6

5

4

3

2

1