Figure 18.1. Cell layers in the human cerebral cortex made visible using Nissl
stain (left), a dye that colors cell bodies but not axons and dendrites, and Golgi
stain (right), which stains only a small fraction of the neurons but stains the
axons and dendrites as well as the cell bodies. Drawings by Ramon y Cajal.It has long been appreciated that individuals may experience
specific problems in their ability to speak, write, or understand lan-
guage after suffering a stroke or other injury to the brain. Aphasia
refers to neurologically based impairment in language function. A pi-
oneer in investigating the neuroanatomy of language was the French
physician Paul Broca (1824-1880). In the mid-1800s Broca performed
postmortem studies of patients who had developed aphasias as a
result of brain injuries sustained during their lifetimes. He found an
association between lesions in the left frontal lobe and the capacity to
speak. “Broca’s aphasia” is now used to describe a condition in which
a person has problems with the production of spoken and written
language. Such an aphasia of language production is often associated
with lesions in the left frontal premotor area of the brain, a region
called Broca’s area (Fig. 18.2).