A Startling Update on Addiction
New research suggests it's not about the pleasure, it's about the craving
Posted May 20, 2015
In a previous blog post, I discussed the role of the brain's reward circuitry in addiction. Briefly, this circuitry consists of clusters of neurons that release the neurotransmitter dopamine. The function of this reward circuitry is to enable us to remember the circumstances that led to the pleasure so we can repeat the behavior and re-experience the pleasure it brought us. Our reward circuitry is vital to our ability to learn. It is what motivates us to get up in the morning and begin another day.
According to the hedonic theory of drug addiction, addiction is nothing more and nothing less than a high-jacking of this normal reward circuitry, a high-jacking that can eventually rob people of their free will to choose. As Wilson and Kuhn so eloquently put it:
“So addiction is far more than seeking pleasure by choice. Nor is it just the willingness to avoid withdrawal symptoms. It is a hijacking of the brain circuitry that controls behavior so that the addict’s behavior is fully directed to drug seeking and use. With repeated drug use, the reward system of the brain becomes subservient to the need for the drug.” Wilson & Kuhn (2005) Cerebrum, 7, 53-66; www.dana.org
A growing body of research suggests that a modification of this theory is in order. For example, rats whose dopamine neurons have been destroyed still appear to enjoy food and sex, but they no longer appear motivated to seek them out. Results like these suggest that drug-induced dopamine release hijacks the brain by inducing craving for the drug, but not pleasure at consuming it. Hence, an addict may be highly motivated to use a drug of choice, yet may derive little pleasure from it. The purpose of the drug seems to be to silence the body's overwhelming craving for it.
Moreover, neuroimaging experiments in humans have shown that not all drugs impact the release or availability of dopamine. Stimulants such as amphetamine and nicotine certainly do. But opiates (such as morphine) and THC (the active component in marijuana) have little impact on dopamine.
Other research with monkeys shows that dopamine neurons spike with unexpected rewards, and their activity is suppressed with unexpected absence of rewards. But they don’t spike when monkeys get an expected reward. These results appear consistent with the opponent process model of drug addiction also discussed in my previous blog.
More about these addiction updates (and references for the work described above) can be found at Dr. Ed Hagan's blog.
Copyright Dr. Denise Cummins May 20, 2015
Dr. Cummins is a research psychologist, an elected Fellow of the Association for Psychological Science, and the author of Good Thinking: Seven Powerful Ideas That Influence the Way We Think.
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