428 Neuroanatomy: Draw It to Know It
Language Disorders
Here, we will learn the major language disorders as a
window into the neuroanatomy of language. First, draw
an outline of a left lateral cerebral hemisphere and then
list the following headings: aphasia, fl uency, comprehen-
sion, and repetition. Note that in regards to the laterality
of language, in 90 % of individuals, the language centers
lie within the left hemisphere, which is why we draw a
left hemisphere, here.^1
Begin with Broca’s aphasia, which is a nonfl uent apha-
sia with preserved comprehension and impaired repeti-
tion. Broca’s aphasia is agrammatic, has a monotonous
(or fl at) melody, and is dysarthric, eff ortful, and hesitant.
Show that Broca’s aphasia localizes to the inferior frontal
g yrus, which is the site of Broca’s area, and also involves
the precentral g yrus, basal ganglia, insula, and related
white matter pathways.^2
Now, list Wernicke’s aphasia, which is a fl uent aphasia
with poor comprehension and impaired repetition. In
Wernicke’s aphasia, there is preserved melody and
rhythm but the speech content is empty or meaningless,
producing a word salad (a high-frequency, unintelligible
jumble of words), and there are paragrammatic and para-
phasic substitution errors, and even the production of
new, meaningless words, called neologisms. Indicate that
the site of injury in Wernicke’s aphasia is the posterior
superior temporal g yrus (Wernicke’s area) and the neigh-
boring supramarginal g yrus and angular g yrus and the
surrounding temporal and parietal lobes and insula.^2
Next, list global aphasia, which is most easily thought
of as a combined Broca’s and Wernicke’s aphasia; it is a
nonfl uent aphasia with poor comprehension and impaired
repetition. Indicate that global aphasia is due to extensive
injury to the left middle cerebral artery territory.^3
Now, list transcortical motor aphasia, which, like
Broca’s aphasia, is a nonfl uent aphasia with preserved
comprehension. However, in transcortical motor apha-
sia, unlike in Broca’s aphasia, repetition is intact. In fact,
make a notation that repetition is such a prominent
aspect of the transcortical aphasias that they all can cause
echolalia — the parrot-like tendency to repeat words
and sentences.^4 Show that transcortical motor aphasia
is commonly due to anterior and middle cerebral artery
watershed injury with resultant injury to the dorsolat-
eral prefrontal cortex and with sparing of the perisyl-
vian region — the presumptive reason for the preserved
repetition.^5 – 7
Next, list transcortical sensory aphasia, which, like
Wernicke’s aphasia, is a fl uent aphasia with poor single-
word comprehension. However, in transcortical sen-
sory aphasia, unlike in Wernicke’s aphasia, repetition is
intact. Indicate that transcortical sensory aphasia is
due to middle and posterior cerebral artery watershed
distribution injury with involvement of the temporo-
parieto-occipital junction and with sparing of the peri-
sylvian region.^5 – 7
Now, list mixed transcortical aphasia, which, like
global aphasia, is a nonfl uent aphasia with poor compre-
hension. However, in mixed transcortical aphasia, unlike
in global aphasia, repetition is intact. Indicate that mixed
transcortical aphasia can occur with combined anterior
and middle cerebral artery and middle and posterior
cerebral artery watershed distribution strokes that spare
the perisylvian region.^5 – 7
Finally, list conduction aphasia, which is essentially
the opposite of mixed transcortical aphasia; it is a fl uent
aphasia with normal comprehension but impaired repe-
tition. In conduction aphasia, speech is hesitant and
paraphasic, presumably from an inability to accurately
transmit the intended word choice from the comprehen-
sion center to the speech production center. Indicate
that conduction aphasia classically localizes to the arcu-
ate fasciculus, most notably, and also to the associated
supramarginal g yrus and insula.^2 Note, however, that
although historically and still commonly we consider
the arcuate fasciculus to be the tract that carries language
from the comprehension center to the production center
(as we have shown, here), this process may actually occur
through the superior longitudinal fasciculus, middle
longitudinal fasciculus, and the extreme capsule (see
Drawing 17-2).^8