In brief, this study was about the relationships between sleep and daytime functioning in people with Parkinson’s disease. Most people think of Parkinson’s disease (we’ll call it “PD” for short) as a motor disorder, involving hand tremors, difficulty walking, limb rigidity etc. The truth is that PD is more than just a motor problem—it’s a whole brain disease that involves a lot of other changes, including mood problems, cognitive deficit, and sleep disturbance. It’s important to look closely at these “non-motor symptoms” because they are actually just as detrimental to a person’s quality of life as the motor symptoms.
My study focused on exploring the relationship between these non-motor symptoms, particularly between sleep and everything else. I wasn’t the first to research these relationships, but I was the first to do so using smartphones! Specifically, I wanted to have people with PD tell me about their symptoms in “real time” throughout the day, as they are living their lives…instead of in retrospect, sitting in the laboratory and trying to recall everything that may have happened in the past month.
Here’s what we did:
Twenty wonderful participants with PD volunteered to participate, and they each came into our lab at Boston University with their smartphones. They first completed a bunch of tests and examinations so we could get a snapshot of their overall mood, cognitive functioning, and general disease severity. Then, we fitted them with an actigraph—basically, a fancy Fitbit that measures activity and estimates sleep parameters—that they would wear for the next two weeks, 24/7. Lastly, we helped them download an app on their phone that would ping them with questionnaires 3 times per day to ask questions about their sleep, mood, thinking, social functioning, and fatigue. After they left the lab, they went on with their regular lives at home and answered the questionnaires each day. When we received their data, we looked at whether the quality or quantity of nighttime sleep could predict their daytime functioning the next day.
Here’s what we found:
First, a huge surprise: Objective sleep variables—that is, the amount and quality of sleep that we could measure with our scientific instruments—was not related to the next day’s mood, cognitive functioning, fatigue, or any other daytime symptom. This really made us scratch our heads, because plenty of other research in the past has shown that for people with PD, sleep is correlated with their other symptoms.
Second, an interesting twist: Subjective sleep quality—that is, how participants themselves felt about their sleep—did predict their mood and cognitive functioning the next day. That’s right, their perception about their sleep was better for predicting their daytime function. And this makes sense in light of previous research—past studies often only asked for patients’ reports about their sleep or only measured it with objective instruments…but not both! Now we know that there could be a discrepancy between these two approaches.
Third, in the other direction: Higher levels of positive mood during the day predicted better subjective sleep quality. This wasn’t too surprising, but it’s also not something we often talk about. Usually sleep researchers focus on what sleep does to other functioning, but I think it’s also important to know what our daytime state does for our sleep.
Here’s what it means:
When doing sleep research with PD participants in the future, we should really make sure to measure both objective and subjective sleep, so we can understand the whole picture
It may be that, for those with mild to moderate PD, how they feel and think about their sleep has a bigger impact on their mood and thinking during the day than their actual sleep quantity/quality.* It’s important to note that this study was only observational, so we don’t know if better sleep perception caused better daytime functioning, only that it statistically predicted better daytime functioning.
If this is true, then psychological factors (e.g., anxiety about sleep or beliefs about sleep) may be a good treatment target. That is, if simply changing how someone feels/thinks about their sleep can improve their daytime functioning…how great would that be? And we do have evidence-based, non-medicine treatments for sleep, and I believe there is potential for us to take advantage them.
I’m very proud to share with you my latest study, hot off the press. We worked with such a lovely group of participants—I am so grateful for their willingness to contribute to research (one of them drove 4 hours to participate!), and our scientific understanding of disease would not be possible without them. In sum, we found that their “real time” objective sleep did not tell us much about their next-day functioning, but that their perception of their sleep did predict their next-day mood and cognition. I think it’s fascinating, and I can’t wait to learn more.
*Note: in our study, we only had participants without major sleep disorders like REM behavior sleep disorder or sleep apnea, so these results may not apply to people with these disorders.