Effects of generalized interictal EEG discharges on sleep stability: assessment by means of cyclic alternating pattern.

Generalized interictal EEG discharges are influenced by a biphasic (phase A and B) modality of arousal control during non-rapid eye movement (REM) sleep termed cyclic alternating pattern (CAP). Each phase A and the following phase B compose a CAP cycle. The percentage ratio of total CAP time to total non-REM sleep time is the CAP rate, a sleep parameter that measures the instability and fragmentation of sleep. Since CAP exerts a powerful influence on generalized interictal EEG discharges during sleep, the polysomnograms of seven epileptic patients affected by a clinically active form of primary generalized epilepsy were matched with those of seven healthy volunteers of the same age and sex to assess the influence of interictal discharges on sleep organization. No remarkable differences emerged when the traditional polysomnographic parameters were compared between the two groups. However, the epileptic patients showed significantly higher CAP rate values (52.7 vs. 34.6\%; p less than 0.003), indicating a greater arousal instability in the sleep records of these subjects. Within the epileptic group, the CAP cycles that included at least one interictal paroxysm were significantly longer than those without EEG discharges (31.2 vs. 25.4 s; p less than 0.007). The selective lengthening of CAP cycles is likely due to an exaggeration of the natural activating power of phase A when coupled with EEG paroxysms and an intensification of the inhibitory properties of the following phase B. The dynamic relationships and differences between spindles in animals, k-complexes, and slow-wave bursts in humans may have a functional linkage with epileptic phenomena during sleep.