Even the most rapacious smokers understand that cigarettes are bad for their health, and many would happily quit the habit, if only they could resist their cravings. So what's actually going on inside the brains of addicted individuals when they are weighing whether to light up?
A new study, published in the journal Proceedings of the National Academy of Sciences, identifies the specific brain regions and circuitry involved in exercising self-control, offering a glimpse into how and why people with addictions give in to craving-inducing triggers. Researchers suggest their findings could help pave the way to developing new therapies for various addictions.
The study, co-authored by neurologist Alain Dagher of the Montreal Neurological Institute and Hospital at McGill University, zeroes in on two key areas of the brain: the medial orbitofrontal cortex, which is involved in assigning value to the potential choices people face, and the dorsolateral prefrontal cortex, which has the ability to increase or decrease that value signal depending on the situation.
The researchers found that by temporarily disabling the dorsolateral prefrontal cortex – using a non-invasive procedure called transcranial magnetic stimulation, which transmits focused magnetic impulses through the skull – they were able to eliminate participants' desire to smoke, reducing craving-related brain signals.
Dagher suggests the findings lend support to the idea that addiction is actually dysfunctional decision-making, a result of abnormal communication between the two areas of the brain.
"What we're saying … is that addiction is a disorder of choice," he says. "It's true that people who are smokers choose to smoke. … But they choose to smoke because of some sort of brain dysfunction and that dysfunction is what makes people addicts."
The study used functional magnetic resonance imaging (fMRI) to scan the brains of 10 moderate-to-heavy smokers on four occasions. On each occasion, the researchers tested different variables, examining what would happen when they inactivated the dorsolateral prefrontal cortex immediately prior to scanning participants' brains, versus when they used a "sham stimulation," where no actual magnetic impulses were applied.
They also tested what would happen if they told the participants not to smoke for four hours after the brain scan, compared with telling participants they could smoke immediately after the scan was finished.
During each scan, participants were shown videos of people smoking, which triggered cravings, and were asked how much they wanted to light up.
The participants' cravings were enhanced when they knew they were permitted to smoke immediately afterward, providing evidence that drug availability strengthens desire. But the scientists found that disabling the dorsolateral prefrontal cortex eliminated that effect.
Unfortunately, one cannot simply do away with cravings once and for all by permanently disabling the dorsolateral prefrontal cortex. Dagher explains that doing so would have serious consequences, since it would hurt one's ability to make rational decisions. Transcranial magnetic stimulation is also not ideal for treating addiction, since its effects on reducing cravings last only up to an hour, he says.
What is promising is that by understanding the mechanisms of self-control, it may be possible to use behavioural therapy or biofeedback to improve brain function to suppress cravings.
"That is one of our next steps – to see how we can try to train up this part of the dorsolateral prefrontal cortex," he says.
Dagher adds: "The main takeaway is that we can use these techniques – brain imaging and transcranial magnetic stimulation – to understand the circuitry of the brain while we're making decisions. So [it's] not just seeing which part of the brain lights up when and how; it's actually understanding what each part of the brain … is contributing to the process of decision-making. And that has implications, not just for drug addiction, but for any condition for which we make decisions."
So how does the decision-making process become disordered in the first place? Dagher says people can be born with a vulnerability to addiction. But certain situations and drugs can alter the communication between the two key areas of the brain. Stress, cocaine and alcohol, for instance, disrupt normal function of the dorsolateral prefrontal cortex, reducing self-control. Nicotine does not, Dagher says, but it activates the medial orbitofrontal cortex, the reward-recognition area of the brain.