Developmental psychology.pdf

102 The Human Organism
Figure 4.11
Electrical Brain Stimulation. Here,
the charge of a Spanish bull is
stopped by stimulating the animal's
brain with a transistorized device and
an implanted electrode. This
stimulation can result in inhibitory as
well as excitatory processes.
The hypothalamus, although not solely responsible for a full emotional experience,
is clearly a necessity. When the cerebral cortex is removed from the cat, an
abbreviated emotional reaction occurs, but when there is no hypothalamus, emotional
arousal is completely absent. Numerous experiments have verified this integrative role
of the hypothalamus in aggressive behavior (Smith & Flynn, 1980; Stoddard-Apter
& MacDonnell, 1980).
An adjacent brain region, lying just forward of the hypothalamus, called the
septal area, has an important connection with the hypothalamus and serves many of
the same functions. It influences the strength of the emotional reaction by sending
impulses to the hypothalamus, and it too can be artificially stimulated by a needle
electrode. Using a transistorized device with the implanted electrode, a Spanish scientist
was able to control the charge of a wild bull (Figure 4.11).
Aversion Centers Hess believed that he had discovered a center for negative
emotions, particularly fear and rage, but some investigators called them sham emotions
because the response seemed so stereotyped. The animals behaved as if they were fearful
or enraged, but perhaps these symptoms lacked the underlying feelings in emotion
(Masserman, 1943). Subsequent research suggested, however, that stimulation in this
region produced both the emotional expression and a negative emotional state, for when
a very weak current was induced, the experimental animal ceased all activity, including
eating. Stimulation through control electrodes in other brain areas produced only a
momentary disruption, not a prolonged avoidance reaction.
The middle and rear hypothalamic regions, in particular, appear responsible
for unpleasant emotions. Stimulation in this concentration of neural tissue provoked
changes in blood pressure and muscle tension, and it disturbed the overall tranquility
of the subject. In fact, brain areas have been intentionally destroyed in psychiatric
procedures, with the aim of producing greater calmness in the patient. Among the
several sites in which this surgery has been performed, an operation in the hypothalamus
has been the most sedative (Sano, 1962).
Pleasure Centers In the mid-1950s Hess's technique was used in a different context,
revealing another dimension of the hypothalamus. A rat with an implanted electrode
was placed in a Skinner box, which is an enclosed chamber with a bar that delivers
food or some other reward when it is pressed. In this case, a press of the bar activated
a weak electric current instead, which was transmitted via the electrode to the animal's
brain. The subject was capable of stimulating itself and to the investigator's surprise,
it eventually did so at the rate of 500 to 5,000 times per hour. Other animals also