1 Epilepsy Center, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
2 Multimodal Functional Imaging Lab, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
3 Magnetoencephalography Center, University of Tübingen, Tübingen, Germany.
4 Department of Neural Dynamics and Magnetoencephalography, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.
5 Center for Integrative Neuroscience, University of Tübingen, Tübingen, Germany.
6 Centre De Recherches Mathématiques, Montreal, Quebec, Canada.
7 Multimodal Functional Imaging Lab, Department of Physics and PERFORM Center, Concordia University, Montreal, Quebec, Canada.
8 Epilepsy Center Kork, Kehl-Kork, Germany.
9 Department of Microsystems Engineering-IMTEK, University of Freiburg, Freiburg, Germany.
10 BrainLinks-BrainTools Center, University of Freiburg, Freiburg, Germany.
11 Department of Neuroradiology, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
12 Department of Neurosurgery, University Hospital Tübingen, Tübingen, Germany.
13 Center for Bionic Intelligence Tübingen Stuttgart, Tübingen, Germany.
14 German Center for Mental Health, Tübingen, Germany.
15 Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.

Objective: Focal cortical dysplasia (FCD) causes drug-resistant epilepsy requiring presurgical evaluation. Invasive electroencephalographic (EEG) studies demonstrate that sleep modulates epileptic activity, including interictal epileptiform discharges (IEDs), fast oscillations (FOs) in the beta (14-40 Hz) and gamma (40-80 Hz) frequency bands, and seizures. This study aimed to quantify sleep-associated changes in IEDs, FOs, and seizures in FCD patients using noninvasive magnetoencephalography (MEG).

Methods: Nineteen patients with FCD were prospectively recruited and underwent simultaneous MEG/EEG recordings lasting 89 ± 19 min during daytime sleep. Sleep stages were classified from the EEG. Beamformer source signals were computed from the MEG signal to enhance sensitivity for visual detection of IEDs, FOs in the beta and gamma frequency bands, and seizures. Magnetic source imaging (MSI) was performed using the Maximum Entropy on the Mean (MEM) method, which is particularly sensitive to the spatial extent of sources, enabling accurate localization of epileptic activity.

Results: N1 sleep was reached in 17 of 19 patients and N2 sleep in 14 of 19 patients. Compared to wakefulness, sleep recordings showed significantly higher rates of FOs and seizures (both p < .05), whereas IED rates showed nonsignificant trends. Ten patients demonstrated FOs or seizures, and 12 showed IEDs. MSI of IEDs demonstrated consistent accuracy across vigilance states, with median Euclidean distances of 12.74 mm (interquartile range [IQR] = 22.74) in wake and 8.34 mm (IQR = 27.58) in sleep, and no systematic amplitude or spatial extent changes. Wavelet-MEM enabled frequency-specific source imaging, with FOs and seizures localizing concordantly to FCD lesions in five of seven and seven of eight patients, respectively.

Significance: Daytime sleep MEG recordings are clinically feasible and significantly enhance the detection of seizures (37% of patients) and FOs compared to wakefulness. Sleep protocols enable noninvasive capture of ictal patterns-the gold standard for epileptogenic zone localization-alongside increased FO rates. These findings support incorporating sleep into standard MEG protocols for presurgical epilepsy evaluation.