Effect of a presleep optokinetic stimulation on rapid eye movements during REM sleep

Some evidence supports the view point that phasic motor events of REM sleep show a complementary relation with the corresponding wake motor activities: (a) an inverse relationship between waking saccades and REM sleep eye movements (REMs) has been found with respect to frequency, amplitude, and direction; (b) an increase of middle-ear muscle activity (MEMA) in the 2 h before sleep causes a complementary decrease of MEMA during REM sleep. The present study evaluated this relation with respect to the optokinetic (OKN) system, assessing the role of automatically induced eye movements in affecting direction and frequency of REMs during sleep. Ten subjects were recorded following standard rules in 3 consecutive nights (one adaptation, one baseline, one experimental). In the experimental night subjects underwent 2 h presleep OKN stimulation at 15 degrees /s. The actual mean number of quick phases of nystagmus induced by the OKN stimulation was 12461.4 +/- 1.7 quick phases/s). No significant effect was found with regard to direction or frequency of REMs; the hypothesis that differences in REM direction and frequency could be modulated by the rank order of REM episodes (i.e., as a function of time elapsed from presleep stimulation) also failed to show any effect of a complementary relation between OKN and REMs. The results suggest that the complementary relation between wake and sleep eye movements is specific for the saccadic system, allowing us to exclude a peripheral mechanism, that is, an effect due to fatigue of extraocular muscles.