The Frontal Cortex

Mo over at Neurophilosophy has an excellent summary of a new paper on near misses and addictive gambling:

Henry Chase and Luke Clark of the Behavioural and Clinical Neuroscience Institute in Cambridge have previously found that the brain responds to near miss gambling outcomes in much the same way it does to as winning. In moderate gamblers, both types of outcome activate the reward circuitry, and although near miss events are experienced to be somewhat less rewarding than wins, they nevertheless increase the desire and motivation to gamble. For games involving skill, near misses indicate an improvement in performance and spur the player to try again. But gambling is a game of chance, which distorts gamblers' thought processes - near misses cause them gambler to overestimate both the level of skill involved and their chances of winning. This spurs them to continue gambling.

The new study extends these earlier observations to regular gamblers, with the aim of establishing whether or not the response to near misses is related to gambling severity. Chase and Clark recruited 24 regular gamblers, The participants were asked to perform a computerized gambling task while their brains were scanned by functional magnetic resonance imaging (fMRI). Two slot machine reels, each with the same six playing icons, were presented to the participants on the screen inside the scanner. In one condition, they were required to select an icon on the left reel and then spin the right reel. In another, the icon was randomly selected for them by a computer. If the icons matched after the reels stopped spinning, they were rewarded with a small amount of money.

After collecting the fMRI data, the researchers focused on the midbrain, which contains neurons that signal reward by releasing the neurotransmitter dopamine. They again found that near misses activate the reward circuits, confirming the results of their previous study. Significantly, they also found that gambling severity, as measured prior to scanning by the South Oaks Gambling Screen, could predict the midbrain's response to a near miss. The more severe a participant's gambling habit, the stronger was the midbrain response to a near miss. In other words, near misses were most rewarding for the pathological gamblers, who experienced them as being almost as rewarding as a win. The participants who gambled less severely also found near misses rewarding, but to a lesser extent.

This data won't surprise Vegas. The details of slot machines are clearly rigged to trick gamblers into thinking they scored a near miss (say, two cherries and a seven) when, in fact, their near miss was just another random event.

The larger question is why this excruciating activity - we're losing money over and over again - is so addictive. The answer, I think, has a lot to do with how our brains process rewards. The popular myth of dopamine is that the neurotransmitter equals pleasure, that it's the hedonist chemical responsible for sex, drugs and rock n' roll. The dopaminergic reality, not surprisingly, is actually much more complicated. Consider the landmark work of Wolfram Schultz. His experiments followed a simple protocol: He played a loud tone, waited for a few seconds, and then squirted a few drops of apple juice into the mouth of a monkey. While the experiment was unfolding, Schultz was probing the dopamine-rich areas of the monkey brain with a needle that monitored the electrical activity inside individual cells. At first the dopamine neurons didn't fire until the juice was delivered; they were responding to the actual reward. However, once the animal learned that the tone preceded the arrival of juice -- this requires only a few trials -- the same neurons began firing at the sound of the tone instead of the sweet reward. And then eventually, if the tone kept on predicting the juice, the cells went silent. They stopped firing altogether. Schultz calls these cells "prediction neurons," since they are more concerned with predicting rewards than actually receiving them.

What's interesting about this system is that it's all about expectation. Our dopamine neurons constantly generate patterns based upon experience: if this, then that. While this neural software normally works great - it's an incredibly efficient form of learning - it gets reliably confused by random systems, from slot machines to Wall Street.

To understand why, it helps to think about the slot machine from the perspective of your dopamine neurons. While you are losing money, your neurons are struggling to decipher the patterns inside the machine. They want to understand the game, to decode the logic of luck, to find the events that predict a payout.

But here's the catch: slot machines can't be solved. They use random number generators to determine their payout. There are no patterns or algorithms to uncover; studying our near-misses won't tell us how to win. There is only a stupid little microchip, churning out arbitrary digits. At this point, our dopamine neurons should just surrender: the slot machine is a waste of mental energy. But this isn't what happens. Instead of getting bored by the haphazard payouts, our dopamine neurons become obsessed. When we pull the lever and get a lucky reward, we experience a rush of pleasurable dopamine precisely because the reward was so unexpected. (According to Wolfram Schultz, such unpredictable rewards are typically three to four times as exciting, at least for our dopamine neurons, than rewards that can be predicted. The clanging coins and flashing lights are like a surprising squirt of juice.) The end result is that we are transfixed by the slot machine, riveted by the fickle nature of its payouts.

A near miss, in other words, isn't just a near miss. It's also a reminder that we almost got a surprising reward, and thus keeps our dopamine neurons from getting bored. Nothing, after all, is quite as nice as that reward we didn't expect.