Effects of sleep on spinal nociceptive reflexes in humans

Controversy continues to surround the monosynaptic and polysynaptic spinal reflexes during the different stages of sleep. In animal studies both of th ese reflexes were found to be depressed during desynchronized sleep. In hum ans, the H reflex was unchanged whereas the second component of the nocicep tive flexion reflex was increased. However, abolition of the H reflex and F waves during REM sleep has also been reported. The aim of this investigation was to examine the effects of different sleep stages on the polysynaptic nociceptive flexion reflex. Six healthy volunte ers were studied. The RIII reflex was studied according to Willer's method (1977) during the different stages of NREM and REM sleep. The RIII reflex threshold was found to increase during stage 2 of NREM slee p, it remained higher during stages 3 and 4. During REM sleep a further inc rease in the reflex threshold was observed. The reflex latency was prolonge d during stage 4 of NREM sleep. There was evidence of further latency prolo ngation during REM sleep. It was also during REM sleep that the maximum inc rease in the amplitude and duration of the reflex were recorded.