Neuromagnetic high-frequency oscillations correlate with seizure severity in absence epilepsy

•Neuromagnetic changes from interictal to ictal periods predominantly occurred in medial prefrontal cortex and parieto-occipito-temporal junction in absence seizures.•Significant differences between interictal and ictal activities were found in low-frequency bands (<30Hz).•The strength of ictal high-frequency oscillations (200–1000Hz) significantly correlated with the severity of absence seizures.