DOMINATIONnecessary condition: it demonstrated that dopamine-deficient rats
liked the treats as much as normal rats. This was important, because if
dopamine-deficient rats no longer wanted Bioserve goodies, the scien-
tists would not be able to test how hard they would work for them.
When no work was required, the dopamine-deprived rats pressed
the lever as many times as the normal rats, and devoured the treats
they had earned. This outcome was not surprising because liking and
enjoying would not be expected to change as a result of a dopamine
alteration. Things did change, though, when the rats had to work
harder:
When the required number of lever presses was increased from
one to four, the normal rats pressed their levers nearly a thousand
times over the course of 30 minutes. The dopamine-depleted
rats weren’t as motivated; they pressed the lever only about six
hundred times.When the requirement was increased to sixteen presses, the
normal rats produced nearly two thousand presses, while the
dopamine-depleted rats barely increased their presses at all. They
were getting only one-quarter the number of treats, but they
wouldn’t work harder.Finally, the requirement was bumped all the way up to sixty-four
presses for a single Bioserve tablet. The normal rats managed
about twenty-five hundred presses—more than one press per
second for the entire 30 minutes. The dopamine-depleted rats
didn’t increase their work at all. In fact, they pressed less than they
had before. They simply gave up.Removing dopamine appeared to diminish a rat’s will to work. But one
more experiment was done to confirm that it was tenacity that was
affected by dopamine destruction, not liking.
Ice cream is always nice, but if you’ve just finished a big meal,
you probably won’t want as much dessert as you would if you hadn’t