Nipa Joshi
will defend her Thesis

Frequency Band Analysis of Auditory Evoked Potentials

Abstract

Several electroencephalograph (EEG) and evoked potential (EP) studies have indicated the occurrence of activity suppression in the brain on arrival of sensory stimuli identical to a previous stimulus. The present study was designed to investigate the frequency characteristics of activity suppression and its spatial extent, as assessed by the P50 and N100 components of auditory evoked potentials (AEPs), which were obtained using double-stimulus paradigm, and analyzed in six non-overlapping frequency bands. The results showed distinct suppression of activity in all frequencies below 50 Hz, and in some subjects, the suppression was distinct even in the gamma2 band (50 – 80 Hz). EPs in the classical EEG bands showed differences in time needed for the activity to reach a maximum after the arrival of a stimulus, and then to die out. In the gamma1 band (18 – 50 Hz), amplitude increase after the arrival of the first and second stimuli was particularly distinct. Spatial distribution map of suppression ratios, calculated using N100, showed highest activity suppression occurring in the parietal region of the brain, whereas, the spatial maps of suppression ratios, calculated using P50, showed highest activity around the parietal and the frontal region of the brain.