Combined influence of cyclic arousability and EEG synchrony on generalizedinterictal discharges within the sleep cycle

Purpose: to analyze the activating role of cyclic alternating pattern (CAP) and EEG synchrony on generalized interictal paroxysms in the first part of the night, when all sleep patterns are represented, Methods: nocturnal pol ysomnographic investigation was accomplished on a randomized series of 18 s ubjects with an active form of primary generalized epilepsy (PGE), but only six patients showed a complete and regular profile of the first two sleep cycles (SCs). Completeness and regularity of the selected SCs consisted in the absence of intervening wakefulness, in the presence of all sleep stages , and in the identification of three main units, (a) a descending branch, d ominated by the build-up of EEG synchrony in the transition from light to d eep non-rapid eye movement (NREM) sleep; (b) a trough, where the magnitude of EEG synchrony is greatest and gives rise to stages 3 and 4; (c) an ascen ding branch characterized by a decrease of EEG synchrony preceding the onse t of rapid eye movement (REM) sleep. Generalized paroxysms were evaluated i n terms of discharge rates (number of interictal bursts per minute of sleep ) and distribution within the investigated sleep parameters. Results: the d ischarge rates decreased from SC1 to SC2, with higher values quantified dur ing NREM sleep (mean, 2.8) compared with REM sleep (mean, 0.8). Both SCs sh owed a progressive decrease of activation across the three units, from the highest discharge rates reached during the descending branches (mean, 3.6) to the more attenuated discharge rates during the troughs (mean, 2.4) down to the lowest rates during the ascending limbs (mean, 1.1). The magnitude o f activation during the descending branches was closely related to the CAP condition (mean, 5.2) and to the powerful effect of phase A (mean, 13.9). T he great majority (82%) of EEG discharges occurring in phase A were distrib uted within the Al subtypes (identified by sequences of k-complexes or delt a bursts). Conclusions: within the first two SCs, the features of NREM slee p endowed with the major activating power on generalized bursts are represe nted by the rise of EEG synchrony (descending branch) and by the A phases o f CAP involved in the regulation of its build-up. (C) 2001 Elsevier Science B.V. All rights reserved.