Gambling is characterized by cognitive distortions in the processing of chance and skill\r\nthat are exacerbated in pathological gambling. Opioid and dopamine dysregulation is\r\nimplicated in pathological gambling, but it is unclear whether these neurotransmitters\r\nmodulate gambling distortions. The objective of the current study was to assess the\r\neffects of the opioid receptor antagonist naltrexone and the dopamine D2 receptor\r\nantagonist haloperidol on gambling behavior. Male recreational gamblers (n = 62) were\r\nassigned to receive single oral doses of naltrexone 50mg, haloperidol 2mg or placebo,\r\nin a parallel-groups design. At 2.5 h post-dosing, participants completed a slot machine\r\ntask to elicit monetary wins, ââ?¬Å?near-misses,ââ?¬Â and a manipulation of personal choice, and\r\na roulette game to elicit two biases in sequential processing, the gamblerââ?¬â?¢s fallacy and\r\nthe hot hand belief. Psychophysiological responses (electrodermal activity and heart rate)\r\nwere taken during the slot machine task, and plasma prolactin increase was assessed.\r\nThe tasks successfully induced the gambling effects of interest. Some of these effects\r\ndiffered across treatment groups, although the direction of effect was not in line with\r\nour predictions. Differences were driven by the naltrexone group, which displayed a\r\ngreater physiological response to wins, and marginally higher confidence ratings on\r\nwinning streaks. Prolactin levels increased in the naltrexone group, but did not differ\r\nbetween haloperidol and placebo, implying that naltrexone but not haloperidol may\r\nhave been functionally active at these doses. Our results support opioid modulation of\r\ncognition during gambling-like tasks, but did not support the more specific hypothesis that\r\nnaltrexone may act to ameliorate cognitive distortions.
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