hearing and vision are unimpaired, a patient with Wernicke’s aphasia
cannot understand—cannot interpret the meaning of—spoken and
written language. Wernicke found this kind of aphasia to be associ-
ated with lesions in a region of the posterior left temporal lobe that
has come to be called Wernicke’s area.
Wernicke’s aphasia is a sensory agnosia specific to language. Like
other sensory agnosias, it is associated with lesions in the cortical
regions near where the temporal, parietal, and occipital lobes come
together. This area of the brain is involved in integration and interpre-
tation of a variety of different kinds of sensory information, coming
from the visual, auditory, and tactile channels. Although patients
with Wernicke’s aphasia can often speak and write, often their spoken
and written language is garbled, sometimes even to the point of being
incomprehensible: twilight car hill frosted gasoline does remarkable
planetary hum pizza.
The findings of Broca and Wernicke in the nineteenth century
suggested that the brain regions involved in human language are
located primarily in the left cerebral hemisphere. Another century
of paying attention to the connection between symptoms of aphasia
and locations of brain lesions demonstrated that, although aphasias
are more often associated with lesions to the left cerebral hemisphere
than to the right, both hemispheres are involved in language. In most
people, nonetheless, the left side of the cerebral cortex is the domi-
nant hemisphere for language production and comprehension.
In some people suffering from severe seizure disorders, small regions
of the cerebral cortex can be pinpointed as the loci of generation of
seizures (see Chapter 7). Procedures have been developed to surgically
locate and excise such regions to reduce the onset and severity of de-
bilitating and life-threatening seizures. Frequently such seizure loci