Interictal Scale-Free Neural Dynamics Identify Epileptogenic Cortex

Background: In epilepsy, clinically useful electrophysiological markers often depend on seizure capture or transient epileptiform events, whereas the broadband aperiodic ``background'' of intracranial recordings is commonly treated as noise. Yet, scale-free spectral structure may reflect an imbalance between excitation and inhibition and cortical instability. Methods: We analyzed interictal intracranial electroencephalography from 55 patients with drug-resistant focal epilepsy using spectral parameterization to quantify aperiodic slope and broadband offset across epileptogenic and non-epileptogenic cortex and across recording modalities. Results: Here, we show that epileptogenic cortex exhibits steeper aperiodic slopes and higher broadband offsets than non-epileptogenic tissue, with these effects remaining robust across stereoelectroencephalography and electrocorticography. These abnormalities are detectable during interictal periods, without seizure capture, indicating that the ongoing background organization of neural activity contains biologically and clinically meaningful information. The findings support a persistent alteration in scale-free cortical dynamics consistent with excitation--inhibition imbalance and identify a compact interictal signature of epileptic network dysfunction. Conclusions: By showing that the aperiodic component of human intracranial recordings is signal rather than noise, this study identifies a seizure-independent and mechanistically grounded marker of epileptic network instability with potential translational value for invasive monitoring.