No one, even scientists
don't exactly understand how emotion is worked out. Yet it is known that the
emotional brain - the limbic system plays an important role in the experience
and expression of emotions. Actually, the limbic system at first is evolved for
evaluating smells, but responding to stimuli and making appropriate emotional
reactions have become more and more important in the limbic system as smelling
has become less important than vision and hearing.
When we are cheerful
or furious, our limbic system is active. But when our limbic system is stimulated
by electrodes, not only we will give emotional reactions but it also leads to
damages and our emotional reactions will become less normal. Besides limbic system,
emotions can be involved in many other brain areas.
Let me give you
an example. A mouse is pressing the button to look for food but suddenly it is
given an electrical shock, 2 things will happen. First, the heart rate of the
mouse will go up and it won't press the button for a moment. These are unlearnt
fears. Later, if an electrical shock is given, it will also ring for a few seconds.
When the mouse is got used to the ringing, the ringing itself will cause the
heart rate of the mouse increases and the mouse can also press the button at
the same time. Then, these are learnt fears of the ringing. Now, if a tiny lesion
is made in the hypothalamus of mouse, its heart rate won't increase but it will
stop pressing the button if the bell rings again. The lesion made inside the
mouse will cancel one of the expressions of learnt fear. But the mouse then later
receives an electrical shock without the ringing, the 2 measures of unlearnt
fear - increasing of the heart rate and the stop of the button pressing will
happen again. As a conclusion, different brain circuits will bring different
learnt fear and unlearnt fears, they are all depended upon the circuits.
