FoundationalConceptsNeuroscience

lateralization of language. For right-handed people, approximately
97 percent have left-hemisphere language dominance, and 3 percent
have right-hemisphere language dominance. For non-right-handed
(meaning left-handed and ambidextrous) people, approximately 70
percent have left-hemisphere language dominance, 15 percent have
right-hemisphere language dominance, and 15 percent have substan-
tial language control by both hemispheres.
Functional brain imaging has also provided additional information
as to precisely which cortical regions are active during various activi-
ties related to language. When listening to spoken language, not sur-
prisingly, neurons are activated in the primary auditory cortex, Al,
just as would happen for any kind of analysis of sound by the auditory
system. If the sounds have a linguistic quality to them—that is, if they
seem to be words strung together in ways that might have meaning—
then in addition to A1, Wernicke’s area is also active. This is true even
if the language being heard is a foreign tongue that is not understood
by the listener. Wernicke’s area may be considered a secondary or
higher-order auditory area, involved in analysis of sounds with lan-
guage-like properties.
Finally, if the language is one that is understood by the listener—
that is, if the words actually carry meaning for the listener—then, in
addition to activity in Al and Wernicke’s areas, there is also activity in
Broca’s area in the frontal lobe. This was a bit of a surprise when it was
first discovered, because for many years Broca’s area was assumed to
be exclusively a motor area. We now know that activity in Broca’s area
is not restricted to speaking and writing but is also relevant for lis-
tening, reading, and understanding language. Neurons in Broca’s area
are in fact premotor mirror neurons, active when observing (reading,
listening, and understanding) language, as well as when generating
(writing and speaking) language.