In the paper my colleagues and I examined the sleep processes of individuals with TBI using polysomnography. Polysomnography is a tool used to measure biophysical changes during sleep and diagnose disorders such as obstructive sleep apnea in which breathing repeatedly stops and starts during sleep, a big problem for individuals with TBI. The contraption is quite uncomfortable (as you can see by the image) and takes some getting used to. Thus, we looked at the "first-night effects" of polysomnography on our subjects to see if the measurements from night-to-night were reliable.
We found that polysomnography was quite reliable on the first night compared to the second night, especially for diagnosing obstructive sleep apnea. This isn't typically the case for the general population so we were a bit surprised. There are a few possible explanations for why individuals with TBI don't seem to experience such first-night effects. One reason is that after a TBI, sleep becomes disrupted due to biological changes in the brain that regulate sleep processes. Thus, when our sample entered the sleep lab, their sleep remained poor on night 1 AND night 2 with little change.
A second possible explanation may be that they were unaffected by novel external environmental stimuli such as the uncomfortable sensors they had to wear or the fact that they weren't in their own bedroom. This explanation is supported by the fact that individuals with TBI tend to have higher amounts of slow-wave sleep (the deep, restful kind). However, our subjects still tended to complain of sleep disturbances and daytime fatigue. Quite the mystery and something that needs to be further explored. I would love to hear your thoughts.
Here is a link to the uncorrected abstract. http://www.ncbi.nlm.nih.gov/pubmed/24990025
Lu W, Cantor J, Aurora RN, Nguyen M, Ashman T, Spielman L, Ambrose A, Krellman J, & Gordon W (2014). Variability of respiration and sleep during polysomnography in individuals with TBI. NeuroRehabilitation PMID: 24990025