One of my general intentions for this blog is to write about the intersection of cognitive neuroscience research and public policy, so it makes sense to begin by highlighting an extraordinarily poor example of how to do that. On December 11th, The New York Times printed an op-ed article by Martin Linstrom describing his neuroimaging research into the efficacy of warnings on cigarette packages
Most of these subjects reported that cigarette warning labels reduced their craving for a cigarette, but their brains told us a different story.
Each subject lay in the scanner for about an hour while we projected on a small screen a series of cigarette package labels from various countries — including statements like “smoking kills” and “smoking causes fatal lung cancers.” We found that the warnings prompted no blood flow to the amygdala, the part of the brain that registers alarm, or to the part of the cortex that would be involved in any effort to register disapproval.
To the contrary, the warning labels backfired: they stimulated the nucleus accumbens, sometimes called the “craving spot,” which lights up on f.M.R.I. whenever a person craves something, whether it’s alcohol, drugs, tobacco or gambling.
It’s hard to know where to begin. Put aside the fact that the article provides no information about what controls were used to derive the results about amygdala and accumbens activation. That’s to be expected from a popular press fMRI study. Even if we accept that viewing cigarette warning labels increases blood flow to the nucleus accumbens (NAcc) but not to the amygdala , Lindstrom’s conclusion is still completely unsupported.
We’ll take the two pieces of evidence in reverse order. First, Lindstrom claims that cigarette labels produce cravings based on the increased activity in the NAcc. While it is true that the NAcc is usually more active when someone is experiencing a craving, that is not the same as saying that increased activity in the NAcc is a craving. To anyone with a basic understanding of the function of dopamine neuron activity, this result should have been wholly unsurprising.
Most drugs of abuse, including nicotine, directly or indirectly elevate dopamine signaling within the NAcc, so scientists have long thought that the NAcc is involved in reinforcement. But drug abuse is a hijacking of this neural system that actually serves a much broader function in general activity. The NAcc is a target for dopaminergic projections from the ventral tegmental area, which contains cell bodies that fire in response to stimuli that reliably predict the delivery of a reward. But these neurons fire in response to rewards ranging from tap water (in thirsty subjects) to online gift-cards. While I would be motivated to work in a study for $20 off at Amazon, it’s not right to say I “crave” the gift card. Of course the sight of a warning label, which appears on the outside of the cigarette box, is going to increase activity in the NAcc. That signal tells the rest of the brain that, if it takes action, it will get a reward. The difference between an effective warning and an ineffective warning is going to depend entirely on what happens next.
Lindstrom argues that cigarette warnings are ineffective because they fail to stimulate the amygdala. The amygdala is involved in a broad range of social behavior, although it is probably best known for responding to threatening images, even when they are flashed for too short a duration to register in conscious awareness. Perhaps, if cigarette warnings did in fact stimulate the amygdala it would provide good evidence of their effectiveness, but it is bizarre to argue the inverse. Cigarette warnings, even those that rely on startling images or statements, could exert their influence in many ways beyond amygdala response. This sort of argument would never make its way into the academic press.
I believe that neuroscience will provide many insights that will help guide policy and that fMRI is a powerful and useful tool. Lindstrom, though, is relying on a drastically oversimplified conception of the way the brain works to justify his shaky conclusions. It is disheartening to see this drivel published in such an influential forum as the New York Times Op-ed page. I generally cheer efforts to communicate brain science to the broader public, but I would hope that the Times does not just serve as a depository for research that would never make its way past academic peer review.
