Ever wondered why it is that when college kids get together, they drink themselves to oblivion? Or why it is that a recovered drug addict finds it almost impossible to resist the temptation when in the company of active users? Or what is it about my wife who feels compelled to “share” my dessert?
Well, wonder no more. A study (albeit preliminary) in the July 7, 2010 online edition of Psychological Science sheds new light on the subject. Helle Larsen and her colleagues of Radboud University Nijmegen in the Netherlands designed an ingenious experiment.
Here’s what they did
They asked 60 women and 53 men to evaluate advertisements for an alcohol-abuse prevention campaign. Each volunteer entered a room that had been furnished as a typical Dutch pub, accompanied by a person of the same sex who the volunteer thought was another participant, but who was actually working with the researchers.
In between two 10-minute evaluation sessions, volunteers and the researchers’ confederates were given a break. An experimenter asked them to sit at a bar stocked with peanuts, beer, wine, soda, and mineral water and to drink whatever they wanted.
As instructed, the confederates took the initiative and drank either two sodas, one alcoholic drink, and then one soda; or three alcoholic drinks for women and four alcoholic drinks for men over a 30-minute period.
DNA analyses of saliva identified 31 volunteers as carriers of the long DRD4 gene, which contains an amino acid sequence that repeats seven times.
What is the DRD4 gene?
DRD4 stands for dopamine receptor D4. Dopamine is a major neurotransmitter of the reward pathways in the brain. The type of reward-producing stimuli can range from emotional to food, to alcohol, to drugs. From an evolutionary point of view, this pathway is important for survival. The pleasure of eating and feeling sated ensures that when energy reserves are low, we feel the urge to satisfy our hunger. Likewise, the bedrock of social interaction is the elicitation of the reward pathway; witness one monkey picking lice off another member of the troop, or closer to home, a mother caressing her child.
The experimental results
In summary, individuals who inherit this particular gene variant (the long form of DRD4) that tweaks the brain’s reward system are especially likely to drink a lot of alcohol in the company of heavy-boozing peers.
When the confederates stuck to sodas or drank one alcoholic beverage, long-gene carriers and non-carriers alike limited themselves to an average of less than half a glass of wine or half a bottle of beer. But when the confederates quaffed multiple alcoholic drinks, carriers of the gene variant consumed an average of almost two wine or beer servings versus almost one serving for non-carriers. These results held for men and women, all of whom said they drink socially, regardless of how much alcohol they reported drinking weekly.
It is striking how common this gene variant is: of the 113 subjects, 31 carried it—about 27%. Even though the numbers in the study are small and the percentages might vary a bit, it is clear that the gene is common.
The gene-environment interaction
In previous posts, we highlighted the interaction of environment with the brain and the genes, which in turn control the body. Optimism and “attitude” can affect the immune response and cancer survival. The brain protein BDNF influences our energy metabolism. Dopamine regulates our social interaction. And a whole cluster of genes affects our longevity.
Early Homo sapiens learned to control their environment, which led to an astounding success of the species. What would be the consequences of understanding and being able to control how our genes and brain react to the environment? It is a prospect both exhilarating and scary to contemplate.