THE CYCLIC ALTERNATING PATTERN PLAYS A GATE-CONTROL ON PERIODIC LIMB MOVEMENTS DURING NON-RAPID EYE-MOVEMENT SLEEP

Periodic limb movements in sleep (PLMS) is a disorder characterized by a cyclic pattern of motor phenomena and EEG changes (mostly arousals) , both recurring at similar to 20- to 40-s intervals. The periodicity of the PLMS phenomena recalls the physiological EEG arousal rhythm of non-rapid eye movement (NREM) sleep known as the cyclic alternating pa ttern (CAP). During CAP, arousals and arousal-equivalent features do n ot appear as isolated events but periodically intrude (phase A) betwee n intervals of background EEG activity (phase B). Though the A phases can be expressed by a variety of EEG patterns, each with a different a rousal impact on polygraphic parameters, overall CAP is a sequence of biphasic cycles reflecting a condition of unstable sleep. Twelve middl e-aged PLMS subjects complaining of poor sleep were polygraphically co mpared with 12 age-matched and gender-matched healthy volunteers (cont rols). With respect to controls, the PLMS recordings showed an enhance ment of the more powerful arousals and presented significantly increas ed amounts of CAP time (+45 min) and CAP rate (+15). Of all the jerks detected in NREM sleep, 92% occurred in CAP, with the great majority o f limb movements (96%) associated with phase A, Ninety-four percent of the nocturnal jerks coupled with phase A started jointly with the ons et of the phase or when the latter had already begun. In particular, m ost of the myoclonic events (67%) occurred in the first 2.5 s of the A phase. The CAP cycles coupled with periodic movements were significan tly longer than those without motor events (+6.4 s). Compared to the A merican Sleep Disorders Association's rules for scoring EEG arousals, the CAP framework offers a more extensive insight into PLMS. In effect , the present study indicates an entrainment of nocturnal myoclonus by means of CAP and sheds light on the complex interactions between arou sal mechanisms and motor phenomena during sleep.