Abstract
Interictal spikes (IS) are one of the major hallmarks of epilepsy. Understanding the factors promoting or suppressing IS would increase our comprehension of epilepsy and possibly open new avenues for therapy. Sleep strongly influences epileptic activity, and the modulatory effects of the different sleep stages on IS have been studied for decades. However, several aspects are still disputed, in particular the role of sleep spindles and slow waves in the activation of IS during Non-REM sleep. Here, we correlate the rate of IS with quantitative measures derived from stereo-EEG during one Non-REM cycle in 10 patients suffering from drug-resistant epilepsy due to type 2 focal cortical dysplasia. We show that the IS rate (ISR) is positively correlated with sigma power (a surrogate for sleep-spindle density) but negatively correlated with delta power (surrogate for slow wave activity). In addition, we present two new indices for quantifying the spatial and temporal instability of sleep. We found that both instability indices are correlated with a high ISR. The main contribution of this study is to confirm the suppressive effect of stable deep sleep on IS. This result might influence future guidelines for therapy of patients suffering from epilepsy and sleep disorders.
Highlights
A better understanding of the mechanisms underlying the generation of interictal epileptic activity would improve our comprehension of epilepsy [1,2,3]
Each NREM-cycle was decomposed into 30 non-overlapping segments, over which we averaged the four EEG parameters and computed the IS rate (ISR) in the seizure-onset zone (SOZ) and Diffusion zone (DZ)
This study contributes to clarify the influence of slow waves, sleep spindles, and sleep instability on ISR during NREM sleep
Summary
A better understanding of the mechanisms underlying the generation of interictal epileptic activity would improve our comprehension of epilepsy [1,2,3]. A large majority of studies indicate that non-rapid-eye-movement (NREM)-sleep increases epileptic activity, whereas REM suppresses both interictal and ictal manifestations of epilepsy [5,6,7,8,9,10,11]. Intracranial EEG is more accurate for the investigation of the relationship between sleep and epilepsy Because it allows the detection of interictal spikes (IS) that are not visible on the scalp [12, 13]; second, because intracranial EEG offers a better spatial resolution highlighting the local behavior of both epileptic and physiological sleep activity [2, 13,14,15]; because the signal-to-noise ratio is higher in invasive than in non-invasive EEG [16]. Using Stero-EEG, it has been demonstrated that the suppressive effect of REM sleep
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