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Chapter 16: The Frontal Lobes
thus derive their information from the object-recognition or motor streams of
Recall that both streams project to the prefrontal cortex, although to different
places (see Figure 16.3), which suggests temporal memory for both motor
and object information, although the memory will be localized in different
places in the frontal cortex. The dorsolateral areas are especially engaged in the
selection of behavior based on temporal memory.
People whose temporal memory is defective become dependent on environmental
cues to determine their behavior. That is, behavior is not under the control
of internalized knowledge but is controlled directly by external cues. One
effect of this condition is that people with frontal-lobe injuries have difficulty
inhibiting behavior directed to external stimuli.
In our dinner-party example, frontal-lobe patients would enter a shoe store
or chat with friends as they responded to environmental cues that they encountered.
We have probably all experienced occasions when the temporal organization
of our behavior failed and we were controlled by external cues rather
than internalized information. How many times have you started to do something,
been distracted by a question or event, and then been unable to recall
what you were going to do? (Sadly, this phenomenon increases with age, which
is not reassuring information about the state of one’s prefrontal cortex.)
One type of environmental cue is feedback about the rewarding properties
of stimuli. For example, if you imagine that a certain stimulus, such as a photograph
of your grandmother, is always associated with a reward, such as wonderful
food, then you learn the association between the visual stimulus (the
photograph of grandma) and the reinforcement (food). Learning such associations
is central to much of what we do as we learn about the world, and the orbitofrontal
cortex is central to learning by association.
We humans live complex lives. We live in social groups in which we have multiple
simultaneous roles as children, parents, friends, siblings, lovers, workers,
and so on. Each role is governed by rules of behavior that we are expected to
follow: our behavior around our grandparents is certainly different from our
behavior with our high-school friends. Similarly, our behavior varies with the
environment: we are quiet at a movie theater or in a library, but we may be
noisy at a football game or at a picnic.
Behavior, then, is context dependent. Hence, behavior that is appropriate at
one moment may not be appropriate if there are subtle changes in the context.
This point is beautifully illustrated in Jane Goodall’s graphic descriptions of the
different behavioral patterns exhibited by chimpanzees.
The makeup of the social group at any given time dictates the behavior of
each chimpanzee. Given the presence and position of certain animals, a particular
chimp may be bold and relaxed, whereas, with a different group of animals,
the chimp is quiet and nervous. Further, an error in evaluating the context can
have grievous consequences.
It may be no accident that the frontal lobe has grown so large in highly social
primates. We can easily see the importance of social context when we reflect on