Developmental psychology.pdf

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Physiology and Behavior 103
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Figure 4.12
Electrical Self-Stimulation. Even as
the number of days of food
deprivation increased, subjects chose
electrical stimulation of the brain in
the hypothalamic region (Spies,
1965).
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Days of food deprivation
behaved as if they were experiencing pleasure, some stimulating themselves 2,000 times
per hour for a full day. So the researcher called this particular brain region, discovered
partly by accident, the pleasure center (Olds, 1956).
Experimental rats were put on a food-deprivation schedule in which they lost
more than one-fourth of their original weight. Yet, when offered a choice of food or
electrical stimulation in a maze, they chose electrical stimulation. Control rats, with
electrodes implanted in other brain regions, preferred the food reward (Figure 4.12).
Eventually this technique was used with chronically depressed or disturbed
persons, and stimulation in some cases produced "a glowing feeling" and other positive
sensations. Further stimulation was sought, just as with the animals (Monroe, Heath,
et al., 1954; Sem-Jacobsen & Torklidsen, 1960).
But the nature of these pleasure centers is still puzzling, especially because
this stimulation sometimes does not have a temporary satiation point, at which the
organism no longer seeks stimulation, as in eating, sexual activity, and so forth. The
motivating effects of this stimulation may be more readily interpreted as some sort of
addiction. In any case, this whole topic has developed into a broad research field now
called intercranial self-stimulation (Olds & Forbes, 1981).
Most important, a very small difference in placement, such as .002 of an inch,
can make a very large difference in reaction. Also, perhaps owing to the intricate nature
of this region, some sites initially appearing as pleasure centers have become aversive
later. The animal abruptly terminates this stimulation for long periods, and
depressive reactions have been observed in psychiatric patients. Such experiments provide
evidence that these brain areas are involved in emotion, but distinctions within
the hypothalamus and other areas need further clarification.
Serendipity in Science According to one version, the discovery of the pleasure
centers shows the difficulty of electrode placement and also the nature of science. James
Olds, the researcher in this instance, was intending to implant the electrode elsewhere,
but the needle was bent in the process. The animal was stimulated in an unexpected
area, and it behaved in an unexpected manner, persistently stimulating itself. Olds then
went on to further studies of this phenomenon (Olds, 1956).
In science a fortuitous, unexpected result is called a serendipitous finding, after
Horace Walpole's story of The Three Princes of Serendip, who were always making
lucky discoveries, finding things for which they were not even searching. In the scientific
process, however, such findings usually do not fall totally to chance. They are
typically uncovered by a well-prepared scientist, ready to perceive the potential significance
of such an event and to take advantage of it.