Analysis of Instantaneous Amplitude and Frequency of Intracranial EEG signal to Characterize Epileptic Seizure Stages

A graphical and analytical description of epileptic seizures based on amplitude modulation and frequency modulation components of intracranial EEG (iEEG) is proposed. This representation allows the characterization of seizures and their different stages from the iEEG by means of triangles whose vertexes are the centroids (c_m) of the signal during preictal, ictal and postictal periods. The centroid is the point defined by the average values of instantaneous amplitude and frequency, a_iand f_i respectively. Data were obtained from 8 patients with recurrent epilepsy, 170 records were processed, 62 of which were seizures and 108 interictal signals. Results show that the centroids of the ictal periods are located in a region of the space a_i - f_i distant from the centroids corresponding to interictal and postictal periods. This original representation of epileptic seizures can facilitate the visualization of stage- transitions and discrimination between the different stages of the iEEG signal. An additional advantage of the method is that the information contained in the signal is synthesized significantly.