or the most part, human motivation is intuitive. From
giving the rats quinine, a bitter liquid, resulted in decidedly
the anxiety of a looming deadline to the enticement
of a cash bonus, positive and negative scenarios are powerful and obvious motivators that dictate how
Needing more than mere facial reactions, Wheeler also measured fluctuations in dopamine, a key neurotransmitter
we respond to a given situation. Behaviorists, like the noted B.F.
in the brain responsible for a wide variety of behavioral and
Skinner, have long studied the ways in which positive reinforce-
cognitive functions, including reward and motivation. Using a
ment affects human behavior and cognition.
technique known as fast-scan cyclic voltammetry, Wheeler was
Dr. Robert Wheeler, an assistant professor of biomedical
able to measure dopamine concentrations, in real time, in one
sciences at Marquette, is interested in negative affective states,
of the brain’s reward centers known as the nucleus accumbens.
those “bad feelings,” which he posits impact life the most.
Not surprisingly, the rats’ dopamine levels spiked significantly
And his research has uncovered a counterintuitive relationship
immediately after the Kool-Aid treat. Turning back to addiction,
between positive and negative reinforcement in cocaine addicts.
Wheeler then wondered: How would the animals react to the
“Positive reinforcement is the best way for us to learn. However, the negative has a profound influence on life,” Wheeler says. “But we don’t have a good neuroscientific understanding of it.” Wheeler focuses his research on what he calls “the tragedy
Kool-Aid when paired with an infusion of cocaine? Taking a prompt from the Pavlovian playbook, Wheeler taught the rats that they would receive cocaine (something they enjoy) immediately after the Kool-Aid (something else they
of addiction,” a disease marked by a cycle of abstinence and
enjoy). Over time, the rats’ dopamine levels measured incredibly
relapse. The relapse, he says, is normal human behavior; how-
low after the administration of the sugary drink. Further, they
ever, it’s also the most tragic part of the disease.
showed decreased reward sensitivity and displayed visually
“As addicts use more and more, they stop doing things they enjoy,” Wheeler says. “They are pushed in one direction at the exclusion of everything else they used to love.” This study of reward-seeking behavior, known as “hedonics,” is helpful in understanding the behavior of those addicted to cocaine and other narcotics. More important, he says, it can
aversive behaviors, such as negative facial expressions. The rats were also given a differently flavored, but similarly sweet, concoction, which resulted in increased dopamine and favorable behaviors. Only the Kool-Aid, which they now associated with cocaine, caused a negative reaction. “It seems counterintuitive, but essentially the cocaine changes
help unravel the intricate neurological circuitries and chemical
the way the rats feel about the Kool-Aid,” Wheeler says. “What
signals that cause these behaviors. And better understanding the
they once loved, they now have no taste for.”
neurophysiology of addiction could lead to improved clinical treatment options.
Wheeler’s findings, published in 2011 in Biological Psychiatry, counter previous research contending that a stimulus
To measure hedonics, Wheeler turned to the same subject
associated with cocaine causes an increase in dopamine and a
that Skinner did: the rat. As a baseline, he first examined how
pleasurable feeling in rats, suggesting that the positive feelings
the animals reacted to something they enjoy — in this case,
promoted drug seeking. “This is important for recognizing and
Kool-Aid. The saccharine-infused water garnered positive facial
hopefully avoiding the complex psychological forces that cause
expressions and mouth movements, which Wheeler says are
relapse in cocaine addicts,” Wheeler notes.
relatively universal among mammals. On the other hand,
But the significance of his work extends beyond combating addiction. Associations are environmental influences that infiltrate everyone’s lives, and Wheeler suggests that negative emotional influences promote other undesired behaviors, such as compulsive overeating and gambling. “We examine decreased dopamine release, reward insensitivity, and drug-seeking behaviors as a way to understand how our environment changes our emotional state and our behavior,” he says. “The next step will be figuring out what we can do about it.” Wheeler adds, “The true value of this work, we hope, is that it contributes to a more complete understanding of the human condition.”² Marquette University
Published on Mar 5, 2013