Blink and you'll miss it : blink rate as a proxy for striatal dopamine in reward-related tasks
Striatal dopamine is critical for motivation to pursue rewards as well as learning from rewarding outcomes in animal models. However, methodological limitations in measuring dopamine in the human striatum have made such findings difficult to verify in humans. Evidence suggests that eye blink rate as a novel but promising indirect indicator of striatal dopamine levels. The current study investigated the role of tonic and phasic dopamine levels in motivation and learning from rewards using eye blink rate as a proxy for striatal dopamine. The project had three phases. In the first, 15 participants completed an instrumental learning task that required them to learn by trial and error in pursuit of monetary reward. However, the data from this phase included multiple blink rates of zero across three or more minutes, so the second phase involved assessing the efficacy of the eye tracker that had been used to track blink rate (an EyeTribe). The EyeTribe produced inconsistent blink rate reports, so the final phase used the EyeLink1000+ eye tracker instead. In the final phase, 88 participants completed the learning task as well as an effort expenditure task that required them to choose between high-effort, high-reward tasks and low-effort, low reward-tasks with various levels of riskiness. The eye tracker recorded participant blink rates at baseline as well as during reward anticipation and reward receipt. Participants also completed self-report measures related to behavioral inhibition and depression. The final phase did not find any significant correlations between blink rate and any of the relevant variables (reward responsiveness, loss avoidance, anticipation, motivation, or depression). These data suggest that blink rate may not be as effective a proxy for striatal dopamine when measured over short time periods, or that eye trackers are ineffective blink recorders.
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