Nocturnal activity and sleep assessment

Sleep occupies approximately one third of our lives yet its modern study has largely been restricted to the use of the polygraph and to self-report via sleep logs. Actigraphy is a method for obtaining objective behavioral samples of nocturnal as well as diurnal activity. Activity is continuously measured and recorded in memory at user specified intervals, usually 1 minute, 24-hours a day for days and weeks if desired. This review concentrates on studies validating actigraphy for sleep assessment and briefly addresses applications to DSM-IV sleep disorders. Sleep onset is a continuous rather than discrete event. A five phase Sleep-Onset Spectrum is discussed and actigraphy is validated within this context.