Actigraphy
Actigraphy estimates sleep and wakefulness from movement recorded by a wrist-worn device, which scores each 30-second slice of the night as sleep or wake.
What it means in practice
In a validation study, actigraphy is recorded at the same time as polysomnography, the full overnight lab sleep study, and the two are compared in 30-second slices of the night called epochs [1]. Sensitivity is how often the device scores sleep when polysomnography shows sleep; specificity is how often it scores wake when polysomnography shows wake [1].
In one validation study of 77 adults in a sleep laboratory, including healthy people, people with a diagnosed sleep disorder and night workers, sensitivity (0.965) and accuracy (0.863) were high but specificity (0.329) was low [1]. In other words, the device recognized sleep well but often scored wake as sleep. Wake after sleep onset averaged 49.1 minutes a night by polysomnography and 36.8 minutes by actigraphy [1]. The authors concluded that actigraphy is a useful and valid way to estimate total sleep time and wake after sleep onset in field and workplace studies, with some limits in specificity [1].
Why it matters when reading nootropics research
The validation study was run in a sleep laboratory, and its conclusion about field and workplace studies is the authors' judgment rather than something the study tested outside the lab [1]. A clinical practice guideline from the American Academy of Sleep Medicine, built on a systematic review and a GRADE assessment of the evidence and written for clinicians assessing patients with sleep disorders, makes conditional (lower-certainty) suggestions to use actigraphy to estimate total sleep time in several of those assessments [2]. Its recommendations apply only to FDA-approved devices and were not written for research in healthy adults [2].
In that validation study, actigraphy's wake estimates were unbiased when wake time was under 30 minutes a night but diverged from polysomnography above that [1], so a difference in actigraphy-measured wake time between a supplement group and a placebo group is read with that limit in mind. Because the device scores each epoch only as sleep or wake [1], it does not give the sleep-stage breakdown that polysomnography reports.
NootropicsWork notes when a sleep finding comes from actigraphy rather than polysomnography, and gives the population and the number of nights recorded.
References
- Marino M, Li Y, Rueschman MN, et al. Measuring sleep: accuracy, sensitivity, and specificity of wrist actigraphy compared to polysomnography. Sleep. 2013.
- Smith MT, McCrae CS, Cheung J, et al. Use of Actigraphy for the Evaluation of Sleep Disorders and Circadian Rhythm Sleep-Wake Disorders: An American Academy of Sleep Medicine Clinical Practice Guideline. J Clin Sleep Med. 2018.