The Effects of slow potential shifts on cognitive potentials on the electroencephalogram

8. ABSTRACT The aim of this study was to investigate cognitive potentials during negative and positive slow potential shifts on the electroencephalogram (EEG). Ten healthy volunteers (5 men and 5 women) whose ages were between 28 and 35 years participated in this study. Event related potentials (ERP) were recorded with electrodes which were placed according to the international 10/20 system from Fz, Cz, Pz, P3, and P4 using the auditory oddball paradigm in an electrically shielded and sound-attenuating, dimly illuminated chamber. The ratio of target stimuli in oddball paradigm used were 20%, and were presented orderly after every four standard stimuli. Interstimulus interval (ISI) was 2000 ms. Amplitude and latency values of N100, P200, and P300 components on the averaged responses of EEG segments that exhibited negative and positive slow potential shifts were evaluated. For assessing the effect of slow potential shifts to the cognitive potentials, the values were submitted to analyses of variance (ANOVA) for repeated measures with two factors: slow potential shift (negative / positive) and channel (Fz / Cz / Pz / P3 / P4). The P300 amplitude was significantly larger during negative slow potential shifts (p<0.05). Furthermore, the slow potential shifts induced significant changes in the topographies of P200 and P300 amplitudes (slow potential shift X channel interaction: p<0.05). The N100 amplitude and latency were only affected by the channel factor (p<0.05), but not by slow potential shifts. The results show that the slow potential shifts determine the arousal level, which in turn has significant effects on the amplitudes of cognitive ERP responses of P300 type. Key Words: Cognitive potentials, Slow potential shifts, DC potentials, Event related potentials, Oddball paradigm. 62