Wednesday, 26 February 2014

Research Briefing: How "Almost Winning" on Slot Machines Evokes Unique Neural Signatures in Gamblers

My colleagues and I have just had a multi-methods imaging study on slot machine gambling published in NeuroImage. The article describes the findings of two studies, one conducted with fMRI and the other with magnetoencephalography MEG, which were part of a large project funded by the Wales Institute of Cognitive Neuroscience (WICN). The NeuroImage article is the culmination of several years' hard work from everyone involved. I can't tell you how relieved I am to finally see it in print! It's certainly been one of the longest duration projects I have ever worked on, and also perhaps the most rewarding because it has taught me the value of interdisciplinary collaboration and how finding answers to the really interesting scientific questions really does require the input of a wide range of subject experts.

Background: The Near-Miss Effect
At the time we started this project, a lot was known about the neurobehavioural mechanisms of the "near-miss effect" in simulated slot machine gambling, thanks mainly to Luke Clark's lab at Cambridge and Mark Dixon's pioneering behavioural work at Southern Illinois (Mike Dixon at Calgary has since down some fantastic work in this regard). The near-miss effect refers to a cluster of findings concerning the neurobehavioural effects of "almost winning". Typically studied using simulated, multi-reel slot machines, near-misses may be defined as a losing display physically resembling a winning display (i.e., two out of three matching symbols on the payout line of three-reel slot). Now, you need three matching symbols to win on a given spin, but 2/3 is deemed closer to a win than, say, a 1/3 display. They are both losses, but the near-miss is subjective and objectively deemed to be almost a win, perhaps due to physical resemblance/generalization.
We know that the proportion of near-misses influences gambling persistence (around a third of trials presenting near-misses is generally thought best), that people (gamblers and non-gamblers alike) rate their chances of winning on the next spin higher than  following losses, that spins following near-misses are usually initiated faster than after other outcomes, and that physiological arousal to near-misses resembles that of actual wins. Studies by Luke Clark, Mark Dixon and colleagues have individually shown that near-misses evoke activation in ventral striatum, rostral anterior cingulate cortex (rACC), and in reward-related neurocircuitry, such as the midbrain (substantia nigra/ventral tegmental). Even the extent of activation is predicted by gambling severity: indeed, the more severe your gambling problem or history is, the greater the activiation seen in anterior insula (bilaterally) in non-gamblers (Clark et al., 2009) and in the midbrain of gamblers (Chase & Clark, 2010).

Of course, there's only so much that fMRI research, with its reliance on the slow haemodynamic BOLD response, can tell us about the brain systems underlying gambling behaviour (I will gladly leave it to others with far better expertise than me to fully explain the issues involved - here and in terms of fMRI vs. MEG, here). Instead, we wished to examine the temporal dynamics and oscillatory changes involved in the near-miss effect and hence chose magnetoencephalography (MEG) as the method to do so.

Our Methods and Predictions
We first measured BOLD-fMRI in a mixed sample of gamblers and non-gamblers and focused on the overlap between activation related to wins and near-misses, and examined the associations with gambling severity and a trait measure of cognitive distortions. We predicted that similar activation patterns would be seen when near-misses were contrasted with losses and when wins were contrasrted with losses. Also, we expected that activitation of the insula to near-misses would be predicted by gambling cognitions.

We designed a simulated, three-reel slot machine task based on Mark Dixon's previous fMRI work. Here's an illustration:

Participants spun the reels, viewed the outcomes and made ratings while lying in the MRI scanner or sitting in the MEG device. We compared separate groups of gamblers and non-gamblers using MEG to investigate induced oscillatory power changes associated with win and near-miss, relative to loss, outcomes. Our focus was on the orbitofrontal cortex (OFC)/ACC and insula regions previously identified in fMRI studies.

By using MEG, we were also able to record EEG at different frequency ranges as well. So, on the basis of previous EEG/ERP work, we were particularly interested in whether near-misses would induce greater theta power, in the 4-7Hz range, in gamblers compared to non-gamblers in our frontal and insula regions of interest.

All participants were administered the South Oaks Gambling Screen (SOGS) and, in the MEG study, their scores determined which group they were assigned to (gamblers or non-gamblers).

Our Findings
Generally, near-misses recruited similar brain regions to wins, including right inferior frontal gyrus and insula. Behaviourally, both gamblers and non-gamblers rated near-misses as closer to a win than a loss (replicating this intriguing effect once again):

BOLD-fMRI responses in the insula to near-misses were associated with the extent to which participants thought about gambling (GRCS) - this neatly replicates an earlier finding from Luke Clark's lab.

Increased theta-band oscillations to near-misses were observed in the insula and right OFC, which were positively associated with gambling severity. The MEG data for R OFC and cognitive distortions related to gambling are shown below:

Taken together, these data show that the near-miss effect in slot machine gambling is underpinned by increases in theta power in R OFC and insula, and which gamblers are particularly sensitive to, and that such increases are associated with the extent to which someone reports cognitive distortions related to gambling and with gambling history/severity. The hope is that the diagnostic and therapeutic implications of these findings might one day be realised by, for instance, devising interventions to attenuate the neural signatures of this near-miss effect.

Dymond, S., Lawrence, N.S., Dunkley, B., Yuen, S.L.K., Hinton, E.C., Dixon, M.R., Hoon, A.E., Munnelly, A., Muthukumaraswamy, S.D., & Singh, K.S. (2014). Almost winning: Induced MEG theta power in insula and orbitofrontal cortex increases during gambling near-misses and is associated with BOLD signal and gambling severity. NeuroImage, 91, 210-219. PDF

Some links to media coverage of our research
Swansea University press release (Poland)
Daily Kos (US)
Science Codex
Electronics Weekly
Medical Xpress  
The Exeter Daily 
Medical Boox
Gaming Zion
Business Standard
Science Daily
National Geographic  
The Economist