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Abstract
Substance use problems are often characterized by dysregulation in reward sensitivity
and inhibitory control. In line with this representation, the goal of this investigation
was to determine how substance abuse tendencies among university students affect incentivized
response inhibition. Additionally, this study examined whether striatal dopamine moderates
the impact of substance use on response inhibition performance. The sample included
ninety-eight university students. Participants completed this prospective experimental
study at an on-campus laboratory. All participants completed substance abuse and disinhibition
subscales of the Externalizing Spectrum Inventory-Brief Form. Using a within-subjects
design, participants then performed the Stop Signal Task under both neutral (unrewarded)
and reward conditions, in which correct response cancellations resulted in a monetary
reward. Striatal tonic dopamine levels were operationalized using spontaneous eyeblink
rate. The outcome measures were Stop Signal Reaction Time (SSRT) performance in the
unrewarded and rewarded phases of the task. A hierarchical linear regression analysis,
controlling for trait disinhibition, age, gender, and cigarette smoking status, identified
an interactive effect of substance use and striatal dopamine levels on incentivized
SSRT. Substance abuse tendencies were associated with slower SSRT and thus poorer
inhibitory control under reward conditions among individuals with low levels of striatal
dopamine ( F = 7.613, p = .007). This work has implications for research examining
advanced drug use trajectories. In situations in which rewards are at stake, drug
users with low tonic dopamine may be more motivated to seek those rewards at the expense
of regulating inhibitory control.