Alcohol intake can increase synapses in neural circuits controlling habitual behavior and reduce synapses in circuits controlling other behaviors.

“For the person that drinks, say, every Thursday night or every Friday night or goes out only on Saturdays but every Saturday, there's evidence that there are changes in the neural circuits of the brain that control habitual behavior and impulsive behavior, and they are modified and strengthened in ways that make those people more habitual and more impulsive outside the times in which they are drinking, and when they drink, impulsive and habitual behavior tends to increase even further.”