GAMBLING is extremely popular, with lottery tickets, casinos, slot machines, bingo halls and other forms of the activity generating revenues of more than £80 billion each year in the UK alone. For most people, gambling is nothing more than an entertaining way to pass the time. But for some, it becomes a compulsive and pathological habit – they spend increasing amounts of time gambling, because tolerance builds up quickly, and experience withdrawal symptoms when they aren’t gambling.
The terms “tolerance” and “withdrawal” are normally associated with drug addiction, and indeed pathological gambling is now considered as being akin to substance abuse. We know, for example, that monetary wins activate the brain’s reward circuitry. In pathological gamblers, however, these responses are dampened, so that increasingly larger wins are needed to produce the same rewarding effects. And according to a new study published in the Journal of Neuroscience, near misses fuel the habit in regular gamblers, because they are almost as rewarding as wins.
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.
Manufacturers of gambling games have apparently known the rewarding effects of near misses all along, and they design slot machines in such a way as to exploit the cognitive distortions of gamblers. Using a technique called clustering, they create a high number of failures that are close to wins, so that what the player sees is a misrepresentation of the probabilities and randomness that the game involves. The gambler who nearly hits the jackpot will therefore want to continue playing, because he thinks he has a good chance of winning.
Chase, H., & Clark, L. (2010). Gambling Severity Predicts Midbrain Response to Near-Miss Outcomes. J. Neurosci. 30: 6180-6187. DOI: 10.1523/JNEUROSCI.5758-09.2010.
Clark, L., et al. (2009). Gambling Near-Misses Enhance Motivation to Gamble and Recruit Win-Related Brain Circuitry. Neuron61: 481-490. [PDF]
Reuter, J., et al. (2005). Pathological gambling is linked to reduced activation of the mesolimbic reward system. Nat. Neurosci. 8:147-148 [PDF]