Time-frequency distribution mappings of somatosensory evoked potentials

Long-latency somatosensory evoked potentials (SEPs) recorded from the human scalp, up to 500 ms after median nerve stimulation, often exhibit a nonstationary nature. The time-frequency amplitude for every SEP was computed by a short-time Fourier transform; short-time periodograms and Wigner transforms were used to calculate SEP energy distribution. In order to study the evolution of signal amplitude or energy at some frequency band of interest, colour mappings of these components over the entire scalp were computed. This approach seems to be very useful for a comprehensive reconstruction of the SEP phenomena in the joint time-frequency domain.<>