How to recruit participants for fMRI study who do not fall asleep during experiment? I'm in a psychology lab and we're having trouble getting participants for an fMRI study. We pay $150 per subject and we need to have several hundred healthy controls for one study. For the 20-minute study, the participant has to look at certain words and think about them, like imagining a scenario where "family" or "pride" was important. 

We keep finding participants from recruiting around campus who will seem enthusiastic, then fall asleep immediately in the scanner. Our IRB states that we have to let them sleep for the full scan and pay them the full amount. I don't know how to prevent this. We've wasted thousands of dollars and weeks to months of time running studies with garbage data. Has anyone figured out how to recruit better participants?
Based on my own experience as a student, the problem is probably not that your participants are lazy... the problem is that, like many university students, they're severely sleep-deprived.

While a student, I once agreed to participate in a friend's (non-MRI) study, which involved listening to sounds and clicking buttons in response. To my embarrassment, despite being enthusiastic about participating, I kept drifting off briefly during the study. I managed to complete it, but I'm sure my results were affected. I'm pretty sure that if I had ever tried to participate in an MRI study, I would have fallen completely asleep.

I don't have experience running MRI studies so I'm not really sure what to suggest to solve this problem, other than to try recruiting from less sleep-deprived populations, or redesigning the study tasks to be more engaging.