Abstract
In order to identify latent bioelectrical oscillators, 15 normal subjects (aged 9-17 years, 8 males, 7 females) were subjected to intermittent photic stimulation. The EEG amplitude spectra corresponding to the 11 fixed frequencies of stimulation presented (3-24 Hz) were combined to form "profiles" of the driving reaction in the right occipital area. The driving response varied with frequency, and was demonstrable in 70-100% of cases (using as criterion peak amplitudes 20% larger than those of the neighbors). The strongest responses were observed at the frequency closest to the alpha peak of the resting EEG. A secondary profile maximum was in the theta band. In 10 subjects, this maximum exceeded half the alpha peak (with an average of 72.4% of the alpha peak), while in the resting spectra, theta amplitudes were much lower than the alpha maxima. This responsiveness in theta activity seems to be characteristic of prepubertal and pubertal subjects. The profiles and resting EEG spectra showed a highly significant Pearson's correlation, with the peak in the theta band of the profiles being the main difference observed between them. The correlation coefficient was significantly correlated with the ratio of the maxima in the theta and alpha bands (R = -0.77, P<0.001). The correlation coefficient between profile and resting spectrum may be a useful indicator in screening methods used to reveal latent cerebral oscillators. Profiles for the second and third harmonics were correlated with those of the first harmonic (fundamental frequency), when considering the corresponding EEG frequencies. Peak frequencies in all three profiles were close to those of the individual's background alpha rhythm, and peak amplitudes in higher harmonics were not much lower than those of the fundamental frequency (mean values of 84 and 63%, for second and third harmonics, respectively).
Highlights
The activation procedures or functional tests enhance the manifestation of latent neurophysiological mechanisms or pre-existing abnormalities, and may induce abnormal findings in an otherwise normal electroencephalogram (EEG) [1]
Intermittent photic stimulation (IPS) has been used to test some basic neurophysiological mechanisms taking into account modern concepts of the organizing role of the bioelectrical rhythms in the brain [11,12]
Some of the individual spectrograms of the EEG with the driving responses to IPS are presented in Figure 2 with an example of a strong reaction to IPS at 3 Hz, especially at the higher harmonics (Figure 2A)
Summary
The activation procedures or functional tests enhance the manifestation of latent neurophysiological mechanisms or pre-existing abnormalities, and may induce abnormal findings in an otherwise normal electroencephalogram (EEG) [1]. A gradual continuous change in frequency of stimulation across the entire EEG frequency range has allowed an individual’s profile of reactivity to be calculated, based on the set of peaks elicited in the EEG spectrogram This profile apparently reflects the characteristic EEG oscillators in different bands [6,8]. The resonance driving peaks coincided with the background peaks, such as those of alpha activity, and appeared at the frequencies where no peaks were observed in the background EEG [6,8] This potential for revealing the individual latent oscillators makes the IPS test very valuable and promising in both clinical and basic neurophysiological studies and permits obtaining additional information not present in the resting EEG [1,13,14,15,16]
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