POKER, though luck is useful when playing it, is essentially a game of skill. Even betting on the horses means assessing the animals’ form and the track’s going. But people who put money into slot machines might just as well stand there burning banknotes. Not for nothing were they once known as one-armed bandits. They mindlessly apply the laws of statistics to confiscate a pre-arranged proportion (usually about 10%) of the money put into them.

Well, not quite mindlessly. For it is possible, while staying within the realm of randomness for the appearance of any given symbol in any given place in the payout row, to tweak things so that “near wins” of two out of three symbols appear quite often. The peculiarities of human psychology are such that some people (a sufficient number, from the house’s point of view) are so pepped by “almost” winning that they are stimulated to carry on playing.

That has been known from behavioural studies for a while. But Simon Dymond of Swansea University, in Britain, wanted to probe more deeply, and has done so, in a study published in NeuroImage, using scanning to explore how the brains of the hooked and the unhooked respond to “almost” beating the bandit.

Dr Dymond and his colleagues compared those brains using two techniques. One was functional magnetic-resonance imaging (fMRI), which shows which parts of the organ are especially active at any given moment. The other was magnetoencephalography (MEG), which measures the electrical nature of that activity. Together, fMRI and MEG enabled them to build a map of each volunteer’s brain as he played on a simulated electronic slot machine.

The team’s particular focus was on a volunteer’s theta response: his brain’s electrical activity in the 4-7Hz range. This has previously been identified as being related to the processing of the experiences of winning and losing—not only in gambling, but in life more generally.

As expected, all volunteers showed high theta responses to wins and low ones to losses. Responses to near wins followed this pattern, but with one exception. They registered similarly in the brains of both pathological gamblers (those addicted to playing slot machines) and non-gamblers, except in part of the brain called the right orbitofrontal cortex. This is significant because that part of the brain has been shown, by other studies, to be involved in the processing of rewards.

Pathological gamblers, Dr Dymond and his team discovered, display similar increases in theta activity in the right orbitofrontal cortex whether they win or “nearly win”: spikes of about 32% and 27% respectively in the strengths of their theta waves. Non-gamblers display the same sort of theta response when they win, but only a 13% increase when they “nearly win”.

Though this discovery is of little immediate use in dealing with the problem of pathological gambling, it does help illuminate what is going on. Theta waves are only a reflection of underlying neurological processes. But they might be used to monitor the effects, and effectiveness, of attempts to break whatever habits of mind it is that are bringing misery to the millions around the world for whom a little flutter becomes something far bigger.