Gambling severity predicts midbrain response to near-miss outcomes.

Gambling is a common recreational activity that becomes dysfunctional in a subset of individuals, with DSM "pathological gambling" regarded as the most severe form. During gambling, players experience a range of cognitive distortions that promote an overestimation of the chances of winning. Near-miss outcomes are thought to fuel these distortions. We observed previously that near misses recruited overlapping circuitry to monetary wins in a study in healthy volunteers (Clark et al., 2009). The present study sought to extend these observations in regular gamblers and relate brain responses to an index of gambling severity. Twenty regular gamblers, who varied in their involvement from recreational playing to probable pathological gambling, were scanned while performing a simplified slot machine task that delivered occasional monetary wins, as well as near-miss and full-miss nonwin outcomes. In the overall group, near-miss outcomes were associated with a significant response in the ventral striatum, which was also recruited by monetary wins. Gambling severity, measured with the South Oaks Gambling Screen, predicted a greater response in the dopaminergic midbrain to near-miss outcomes. This effect survived controlling for clinical comorbidities that were present in the regular gamblers. Gambling severity did not predict win-related responses in the midbrain or elsewhere. These results demonstrate that near-miss events during gambling recruit reward-related brain circuitry in regular players. An association with gambling severity in the midbrain suggests that near-miss outcomes may enhance dopamine transmission in disordered gambling, which extends neurobiological similarities between pathological gambling and drug addiction.