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Chapter 8
image. Subcortical areas such as the thalamus and basal gan-
glia may also be directly involved in conscious experience, but
it seems that the hippocampus and cerebellum are not.
Saying that we can use one set of neurons and then shift
to a new set at a later time may be the same as saying we can
focus attention on—that is, bring into conscious awareness—
one object or event and then shift our focus of attention to
another object or event at a later time. Thus, the mechanisms
of conscious awareness and attention must be intimately
related.
Motivation and Emotion
Motivation is a factor in most, if not all, behaviors, while
emotions accompany many of our conscious experiences.
Motivated behaviors such as sexual behaviors play a part in
controlling much of our day-to-day behavior, while emotions
may help us to achieve the goals we set for ourselves as well as
express our feelings.
Motivation
Those processes responsible for the goal-directed quality of
behavior are the
motivations,
or “drives” for that behavior.
Motivation can lead to hormonal, autonomic, and behavioral
responses.
Primary motivated behavior
is behavior related
directly to homeostasis—that is, the maintenance of a relatively
stable internal environment, such as getting something to
drink when you are thirsty. In such homeostatic goal-directed
behavior, specifi c body “needs” are satisfi ed. Thus, in our
example, the perception of need results from a drop in body
water concentration, and the correlate of need satisfaction is
the return of body water concentration to normal. We will dis-
cuss the neurophysiological integration of much homeostatic
goal-directed behavior later (thirst and drinking, Chapter 14;
food intake and temperature regulation, Chapter 16).
In many kinds of behavior, however, the relation between
the behavior and the primary goal is indirect. For example,
the selection of a particular fl
avor of soft drink has little if any
apparent relation to homeostasis. The motivation in this case is
secondary. Much of human behavior fi ts into this latter category
and is infl uenced by habit, learning, intellect, and emotions—
factors that can be lumped together under the term “incen-
tives.” Often, it is diffi cult to distinguish between primary and
secondary goals. For instance, you may fi nd certain foods more
appealing if you are defi
cient in some of the elements in that
food. Sometimes the primary homeostatic goals and secondary
goals confl ict, as, for example, during a religious fast.
The concepts of reward and punishment are inseparable
from motivation. Rewards are things that organisms work
for or things that make the behavior that leads to them occur
more often—in other words, positive reinforcers. Punishments
are the opposite.
The neural system subserving reward and punishment is
part of the reticular activating system, which you will recall
arises in the brainstem and comprises several components. The
component involved in motivation is known as the
mesolim-
bic dopamine pathway
meso-
because it arises in the mid-
brain (mesencephalon) area of the brainstem;
limbic
because it
goes to areas of the limbic system, such as the prefrontal cor-
tex, the nucleus accumbens, and the under-surface of the fron-
tal lobe (
Figure 8–9
); and
dopamine
because its fi bers release
the neurotransmitter dopamine. The mesolimbic dopamine
pathway is implicated in evaluating the availability of incen-
tives and reinforcers (asking, “Is it worth it?” for example) and
translating the evaluation into action.
Much of the available information concerning the neural
substrates of motivation has been obtained by studying behav-
ioral responses of animals to rewarding or punishing stimuli.
One way in which this can be done is by using the technique of
brain self-stimulation.
In this technique, an unanesthetized
experimental animal regulates the rate at which electric stimuli
are delivered through electrodes implanted in discrete brain
areas. The small electrical charges given to the brain cause the
local neurons to depolarize, thus mimicking what might hap-
pen if these neurons were to fi re spontaneously. The experi-
mental animal is placed in a box containing a lever it can press
(
Figure 8–10
). If no stimulus is delivered to the brain when
the bar is pressed, the animal usually presses it occasionally at
random.
If, in contrast, a stimulus is delivered to the brain as a
result of a bar press, a different behavior occurs, depending on
the location of the electrodes. If the animal increases the bar-
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Model
Patient’s copy
Figure 8–8
Unilateral visual neglect in a patient with right parietal lobe damage.
Although patients such as these are not impaired visually, they do
not perceive part of their visual world. The drawings on the right
were copied by the patient from the drawings on the left.
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