I think it measured reaction times. I thought I found it once, about a year ago. I'll look again.
edit:
Pretty easy to find this one, but I don't know if it's the only one:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1739867/
Thanks. Looks like my hunch was right, at least as far as this study is concerned, in that it focuses on performance, which is a different issue than the lowering of inhibitions.
An important implication of this is that declining to fly while impaired could be more likely for a person suffering from sleep deprivation than it is for someone who is inebriated.