This article describes the two techniques of measuring when a person is asleep: actigraphy and polysomnography.
KANADY, J. C., DRUMMOND, S. P. A. and MEDNICK, S. C. (2011), Actigraphic assessment of a polysomnographic-recorded nap: a validation study. Journal of Sleep Research, 20: 214–222. doi: 10.1111/j.1365-2869.2010.00858.x
Polysomnography (PSG) monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.
Actigraphy is done by a portable device usually worn around the wrist or ankle that registers movement. Actigraphy is much less cumbersome and invasive, and therefore more suitable to naturalistic and long term experiments.
The present study aims to determine if actigraphy can detect accurately sleep in healthy, young adults during a 90-min mid-afternoon nap opportunity when compared to PSG.
actigraphy was fairly proficient in distinguishing the difference between a nap and a no-nap period of quiet rest. Although actigraphy overestimated sleep during the no-nap condition, the accuracy values remained reasonably high