Argiro ME, Chrissanthi HD, Charalambos PC, Miltiades KA, Andreas RD, Christos CN. Principal component analysis of the P600 waveform: RF and gender effects. Neurosci Lett. Apr 29, 2010 Ahead of print.
Event-related potentials (ERPs) reflect the brain’s electrical response to stimuli. The P600 component of ERPs, or late positive potentials, is elicited 500-800 milliseconds after stimuli. This component has been associated with linguistic processes and working memory (WM). Principal component analysis (PCA) complements traditional analysis of ERP waveform (amplitudes and latencies). It allows for a more informative spatio-temporal configuration of the changes in the recorded electric field. In previous electroencephalographic (EEG) studies it was found that the EEG energy of males was greater than that of females and that radiofrequency radiation (RF) affected electric activity of the brain in a gender-specific manner: it decreased EEG energy of males and increased that of females.
The objective of this study was to use principal component analysis for analysis of amplitudes and latencies of the P600 waveform of ERP elicited during the performance of a working memory task in the presence and absence of RF, and to examine gender-related differences in the patterns.
Two separate experiments were conducted. In the first experiment, 19 healthy individuals (9 men and 10 women, mean age 23.3±2.23 years, mean education 16.9±1.82 years) were exposed to 900 MHz signal with mean power at 64 mW. In the second experiment, 20 healthy individuals (10 men and 10 women, mean age 22.75±2.71 years, mean education 16.3±2.71 years) were exposed to 1800 MHz signal with mean power at 128 mW. The signal was not modulated in both experiments. The cognitive task was the digit span Wechsler Auditory test. The subjects performed the task twice in a single-blind random order with and without RF with a two-week interval between the measurements. At each trial, EEG activity was recorded from 15 Ag/AgCl scalp electrodes. The amplitude and latency of the P600 peak in the interval 500-800 milliseconds after the stimulus was calculated. Repeated measures ANOVA and Principal component analysis (PCA) were used for data analysis.
Repeated measures ANOVA and PCA produced congruent results. The mean values of the P600 amplitudes at the 15 electrodes were significantly different. The mean value of the amplitudes of the anterior electrodes was significantly lower than that of the posterior electrodes, and the mean value of the central electrodes was between these two. The mean values of the P600 latencies at the 15 electrodes were also significantly different. The mean value of the latencies of the anterior electrodes was significantly higher than that of the posterior electrodes, and the mean latencies of the central electrodes were in between. Activation of the P600 component occurred early and more intensely in the region of the posterior electrodes and less intensely in the area of central electrodes. The activation of the anterior electrodes occurred ~40 milliseconds later with considerably less intensity. The effect of gender was evident in the anterior electrodes with regards to the amplitudes and in the central electrodes with regard to the latencies. In the absence of RF, women had significantly lower amplitudes and lower latencies than men. Exposure to both 900 MHz and 1800 Hz signals alleviated these differences.
Interpretation and Conclusion
It has been demonstrated that there are gender-related differences in P600 latencies and amplitudes in the absence of RF exposure, and that these differences disappear in the presence of RF exposure. This RF-gender interaction may be explained by the gender-related information processing and the nature of the interaction of RF radiation with biological systems. PCA procedure provides an adequate model of the spatially distributed event-related dynamics corresponding to the P600 waveform.