Motor events during healthy sleep: a quantitative polysomnographic study

Study objectives: Many sleep disorders are characterized by increased motor activity during sleep. In contrast, studies on motor activity during physiological sleep are largely lacking. We quantitatively investigated a large range of motor phenomena during polysomnography in physiological sleep.

Design: Prospective polysomnographic investigation.

Setting: Academic referral sleep laboratory.

Participants: One hundred healthy sleepers age 19-77 y were strictly selected from a representative population sample by a two-step screening procedure.

Interventions: N/A.

Measurements and results: Polysomnography according to American Academy of Sleep Medicine (AASM) standards was performed, and quantitative normative values were established for periodic limb movements in sleep (PLMS), high frequency leg movements (HFLM), fragmentary myoclonus (FM), neck myoclonus (NM), and rapid eye movement (REM)-related electromyographic (EMG) activity. Thirty-six subjects had a PLMS index > 5/h, 18 had a PLMS index > 15/h (90th percentile: 24.8/h). Thirty-three subjects had HFLM (90th percentile: four sequences/night). All subjects had FM (90th percentile 143.7/h sleep). Nine subjects fulfilled AASM criteria for excessive FM. Thirty-five subjects had NM (90th percentile: 8.8/h REM sleep). For REM sleep, different EMG activity measures for the mentalis and flexor digitorum superficialis muscles were calculated: the 90th percentile for phasic mentalis EMG activity for 30-sec epochs according to AASM recommendation was 15.6%, and for tonic mentalis EMG activity 2.6%. Twenty-five subjects exceeded the recently proposed phasic mentalis cutoff of 11%. None of the subjects exceeded the tonic mentalis cutoff of 9.6%.

Conclusion: Quantification of motor phenomena is a basic prerequisite to develop normative values, and is a first step toward a more precise description of the various motor phenomena present during sleep. Because rates of motor events were unexpectedly high even in physiological sleep, the future use of normative values for both research and clinical routine is essential.