Gambling disorder sufferers prefer immediately larger rewards despite long term losses on the Iowa
Gambling Task (IGT), and these impairments are associated with
dopamine dysfunctions.
Dopamine is a
neurotransmitter linked with temporal and structural dysfunctions in
substance use disorder, which has supported the idea of impaired decision-making and
dopamine dysfunctions in
gambling disorder. However, evidence from
substance use disorders cannot be directly transferred to
gambling disorder. This article focuses on three hypotheses of
dopamine dysfunctions in
gambling disorder, which appear to be "fallacies," i.e., have not been supported in a series of positron emission tomography (PET) studies. The first "fallacy" suggests that
gambling disorder sufferers have lower
dopamine receptor availability, as seen in
substance use disorders. However, no evidence supported this hypothesis. The second "fallacy" suggests that maladaptive decision-making in
gambling disorder is associated with higher
dopamine release during
gambling. No evidence supported the hypothesis, and the literature on
substance use disorders offers limited support for this hypothesis. The third "fallacy" suggests that maladaptive decision-making in
gambling disorder is associated with higher
dopamine release during winning. The evidence did not support this hypothesis either. Instead, dopaminergic coding of reward prediction and uncertainty might better account for
dopamine dysfunctions in
gambling disorder. Studies of reward prediction and reward uncertainty show a sustained
dopamine response toward stimuli with maximum uncertainty, which may explain the continued
dopamine release and
gambling despite losses in
gambling disorder. The findings from the studies presented here are consistent with the notion of dopaminergic dysfunctions of reward prediction and reward uncertainty signals in
gambling disorder.