Despikifying SEEG signals using a temporal basis set

The current trend in the diagnosis of epilepsy is oriented towards high frequency activity that is used to characterize the epileptogenic zone. Still, interictal spikes, i.e. transient activity, remain a classical marker. A difficult question is to separate these two classes of activity that overlap in the time-frequency plane. We propose to use a temporal basis set in order to describe and subtract spiking activity from the traces, as a preprocessing step for further space-time-frequency analysis. The set is based on singular value decomposition. We select the first three temporal components, construct a model of the spikes by projecting the data on the new basis and obtain a spike-free signal by subtracting the model from the original signal. We prove that despikifying results in a better characterization of oscillatory activity, promoting time and frequency separation. The resulting spatio-temporal maps could help for a better characterization of the oscillatory activity in electrophysiology of epilepsy.