212 Chapter 8
others. These abilities are required for the acquisition of social
skills and perhaps also of language, a possibility supported by
the observation that human mirror neurons are found in Broca’s
area, needed for language (see fig. 8.14 ). Because autism, bet-
ter termed autism spectrum disorder, involves impairments in
social interactions, the ability to imitate other people, language
ability, and empathy (among other symptoms), some scientists
have proposed that autism may be at least partly due to impair-
ment of mirror neuron function.Visualizing the Brain
Several relatively new imaging techniques permit the brains
of living people to be observed in detail for medical and re-
search purposes. The first of these to be developed was x-ray
computed tomography (CT). CT involves complex computer
manipulation of data obtained from x-ray absorption by tissues
of different densities. Using this technique, soft tissues such as
the brain can be observed at different depths.
The next technique to be developed was positron emission
tomography (PET). In this technique, radioisotopes that emit
positrons are injected into the bloodstream. Positrons are like
electrons but carry a positive charge. The collision of a positron
and an electron results in their mutual annihilation and the emis-
sion of gamma rays, which can be detected and used to pinpoint
brain cells that are most active. Medically, PET scans are used to
determine the stage of cancer and to monitor patient responses
to cancer treatments. Scientists have used PET to study brain
metabolism, drug distribution in the brain, and changes in blood
flow as a result of brain activity. For example, PET was used
in a recent study of volunteers who were injected with (^18 F)
fluorodeoxyglucose to measure how the glucose metabolism
of the brain was affected by cell phone use: metabolism was
increased in regions closest to the antenna after prolonged
exposure.
A newer technique for visualizing the living brain is
magnetic resonance imaging (MRI). This technique is basedinvolved in the interpretation and association of auditory and
visual information. The occipital lobe is the primary area
responsible for vision and for the coordination of eye move-
ments. The functions of the temporal and occipital lobes will
be considered in more detail in chapter 10, in conjunction with
the physiology of hearing and vision.
The insula ( fig. 8.7 ) is implicated in the encoding of mem-
ory and in the integration of sensory information with visceral
responses. It receives olfactory, gustatory (taste), auditory,
and somatosensory (principally pain) information, and helps
control autonomic responses to the viscera and cardiovascu-
lar system. Because it receives sensory information from the
viscera, it is believed to be important in assessing the bodily
states that accompany emotions. One study demonstrated that
those neurons that fire in response to pain applied to the hand
also fire when the subject was told that pain would be applied
to the hand of a loved one; in another study, the neurons within
the insula that responded to a disgusting odor also fired when
the subject saw an expression of disgust in another person.
Studies first performed in macaques demonstrated neurons
in the frontal and parietal lobes that fired when the monkeys
performed goal-directed actions and when they observed oth-
ers (monkeys and people) perform the same actions. These neu-
rons, termed mirror neurons, have been identified using fMRI
(discussed next) in similar locations in the human brain. Mir-
ror neurons in the premotor areas of the frontal lobes become
active when a person performs a goal-directed action or sees
another individual perform the same action. Other mirror neu-
rons involved in higher somatosensory processing in the pari-
etal lobe respond when a person is touched in a body location
or sees another individual touched in the same location. Mirror
neurons also have neural connections to the insula ( fig. 8.7 )
and cingulate gyrus (see fig. 8.18 ), which can provide an affec-
tive (emotional) component to the vicarious experience.
Scientists believe that mirror neurons are involved in the
ability to imitate others, understand the intentions and behav-
ior of others, and empathize with the emotions displayed by
Figure 8.8 An MRI image of the brain reveals the sensory cortex. The integration of MRI and EEG information shows the
location on the sensory cortex that corresponds to each of the digits of the hand.