The release of dopamine forms the basis for nicotine, cocaine, and gambling addictions. The inhalation of nicotine triggers a small dopamine release, and a smoker quickly becomes addicted. Cocaine and heroin deliver bigger dopamine jolts, and are even more destructive.

In the past, companies used customer surveys, focus groups, interviews, and psychological tests to figure out how to make products more appealing to customers. In 1957, Vance Packard published The Hidden Persuaders, in which he identified eight hidden needs -- including a consumer's desire to love and be loved, or a yearning for power -- which advertisers could exploit to create demand for their products.

Packard, who questioned the morality of exploiting emotions in order to sell products, died in 1996. Were he alive today, he would surely be shocked to see how primitive the exploitation techniques he described now seem.

Today we can monitor the brain's response with NMR (nuclear magnetic resonance) imaging to more accurately measure what people are experiencing when they play online games, interact with smart devices, or gamble. Luke Clark, a neuroscientist at the University of Cambridge, used brain scans to determine that when gamblers felt they could exert control over a game's outcome -- for example, by throwing the dice harder, or pulling the lever on a slot machine with more force -- it increased their interest in playing. Also, such near misses as getting two out of three matching symbols on a slot machine stimulated the desire to continue to play. Other experiments have shown that optimizing a slot machine's frequency of near misses can extend gambling times by 30 percent. Neuroscientists have also found that it is the unpredictability of winning large rewards that stimulates the dopamine releases that compels gamblers to return.

In the 1990s, concern over obsessive-compulsive behavior associated with computer games and the Internet began to grow. Until roughly 2000, compulsive behavior remained a side effect -- not an intentional element of game design and other Internet applications. Application providers were simply supplying customers with services that made their products more appealing.

In the past, society has been able to put physical barriers in place to make it more difficult to satisfy unhealthy obsessions. Things are very different today.

But before long, people were referring to their BlackBerries as CrackBerries, and parents were beginning to worry about the number of hours their kids spent on video games. We now believe that the compulsion to continually check email, stock prices, and sporting scores on smartphones is driven in some cases by dopamine releases that occur in anticipation of receiving good news. Indeed, we have grown so addicted to our smartphones that we now experience "phantom smartphone buzzing," which tricks our brains into thinking our phone is vibrating when it isn't.