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THE PROMISE OF REWARD
Once Olds and Milner had discovered the “pleasure” center of their rat’s brain, they set to work
demonstrating just how euphoric stimulating this area of the brain was. First they starved the rat for
twenty-four hours, then placed him in the middle of a short tunnel with food at both ends. Normally,
the rat would run to one end and gobble down the rat chow. But if they shocked the rat before he made
it to the food, he would stop at that spot and never budge. He preferred to wait for the possibility of
another shock rather than the guaranteed reward of food.
The scientists also tested whether the rat would shock himself if given the opportunity. They set up
a lever that, when pressed, would electrically stimulate the rat’s pleasure center. Once the rat figured
out what the lever did, he began giving himself shocks every five seconds. Other rats given free
access to self-stimulation showed no signs of satiation, and would continue to press the lever until
they collapsed from exhaustion. Rats even found self-torture acceptable if it led to brain stimulation.
Olds put self-stimulating levers at the opposite ends of an electrified grid, and set it up so that a rat
could only receive one shock at a time from each lever. Rats willingly ran back and forth across the
electrified grid until their charred feet were so injured they could not continue. Olds became even
more convinced that the only thing that could produce this behavior was bliss.
It didn’t take long for a psychiatrist to think this experiment would be a pretty neat thing to try with
humans.
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At Tulane University, Robert Heath implanted electrodes into his patients’ brains, and gave
them a control box to self-stimulate the newly discovered pleasure center. Heath’s patients behaved
remarkably like Olds and Milner’s rats. When given permission to self-stimulate at any rate they
liked, they averaged forty shocks per minute. When a food tray was brought in for a break, the patients
—who admitted they were hungry—didn’t want to stop the self-stimulation to eat. One patient put up
vigorous protests whenever the experimenter tried to end the session and disconnect the electrodes.
Another participant continued to press the button over two hundred times
after
the current was turned
off, until the experimenter finally demanded that he stop.
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Somehow these results convinced Heath
that self-stimulation of the brain was a viable therapeutic technique for a wide range of mental
disorders (heck, they seemed to like it), and he decided it would be a good idea to leave the
electrodes in his patients’ brains and give them small portable self-stimulators they could wear on
their belts and use whenever they wanted.
At this point, we should consider the context of this research. The dominant scientific paradigm at
the time was behaviorism. Behaviorists believed the only thing worth measuring—in animals or
humans—was
behavior
. Thoughts? Feelings? Waste of time. If an objective observer couldn’t see it,
it wasn’t science, and it wasn’t important. This may be why early reports of Heath’s work lack any
detailed firsthand reports from his patients about what the self-stimulation felt like. Heath, like Olds
and Milner, assumed that because his subjects continuously self-stimulated, and ignored food for the
opportunity to keep shocking themselves, they were being “rewarded” for it with euphoric pleasure.
And it’s true that the patients said the shocks felt good. But their near-constant rates of self-
stimulation, combined with anxiety about having the current turned off, suggested something other than
true satisfaction. What few details we have about his patients’ thoughts and feelings reveal another
side to this seemingly blissful experience. One patient, who suffered from narcolepsy and was given
the portable implant to help him stay awake, described the feeling of self-stimulation as intensely
frustrating. Despite his “frequent, sometimes frantic pushing of the button,” he was never able to
achieve the sense of satisfaction he felt he was close to experiencing. The self-stimulation left him
anxious, not happy. His behavior looked more like compulsion than a man experiencing pleasure.
What if Olds and Milner’s rats weren’t self-stimulating to exhaustion because it felt so good that
they didn’t want to stop? What if the area of the brain they were stimulating wasn’t rewarding them
with the experience of profound pleasure, but simply
promising
them the experience of pleasure? Is it
possible the rats were self-stimulating because their brains were telling them that if they just pressed
that lever one more time, something wonderful was going to happen?
Olds and Milner hadn’t discovered the pleasure center—they had discovered what neuroscientists
now call the
reward
system. The area they were stimulating was part of the brain’s most primitive
motivational system, one that evolved to propel us toward action and consumption. That’s why Olds
and Milner’s first rat kept hanging around the corner where he was first stimulated, and why the rats
were willing to forgo food and electrocute their feet for the chance at another brain jolt. Each time the
area was activated, the rat’s brain said, “Do this again! This will make you feel good!” Every
stimulation encouraged the rat to seek more stimulation, but the stimulation itself never brought
satisfaction.
As you will see, it’s not just electrodes in the brain that can trigger this system. Our whole world is
full of stimuli—from restaurant menus and catalogs to lottery tickets and television ads—that can turn
us into the human version of Olds and Milner’s rat chasing the promise of happiness. When that
happens, our brains become obsessed with “I want,” and it gets harder to say, “I won’t.”
“Promise of Reward” System of Midbrain
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