Effects of flicker stimulation on electroencephalography during resting (with eyes open or closed) and during performance of mental calcuations (with eyes closed)

Abstract

The purpose of this study was to examine the effects of flicker stimulation of varying frequencies upon the EEG patterns under 3 different conditions: eyes closed (EC) and eyes opened (EO) both in resting state and mental calculation with eyes closed (MC).10 male and 10 female adults were individually introduced, into a sound-proofed and electrically shielded, dark room where the EEG was recorded monopolarly from the frontal, temporal, vertex, and occipital needle electrodes with reference to the right earlobe and was simultaneously frequency-analyzed by a Walter-type analyzer which permitted 10-sec epoch analyses of the occipital EEG through 10 band pass filters (Table 1). Flickering lights of varying frequencies (Table 1) were presented under the 3 different conditions (EC, MC and EO). For 5 Ss the procedure was repeated 3 times with an interval of about a week or more in order to assess the reliability of the cortical response (EEG) patterns.The results were based on the cortical responses in terms of the integrated values per 10 sec expressed by analyzer pen deflection in mm through the 5 band pass filters covering alpha and beta ranges. The cortical responses in integrated values were highest under EC and lowest under EO, indicating a greater blocking effect under EO than under MC; in addition, in accordance with Motokizawa (1963), not only alpha but also beta responses were suppressed under EO. Fig. 2 indicates highly constant EEG patterns (band spectra) in 3 replications. Moreover, intrasubject correlations in band spectra were considerably high, especially under EC (mean rs=0.80). When the Ss were classified into 3 types (R, P and M) of the alpha response following Walter (1953), the obtained distribution was about identical to his findings.Photic driving has been variously defined by different authors. First, it was defined in terms of cortical responses under photic intermittent stimulation, and second in terms of the difference between cortical responses under the stimulation and those under no such stimulation. This second definition is evidently superior to the first since spontaneous responses are excluded but it still neglects nonspecific arousal effects (alpha blocking in alpha ranges) of the photic stimulation itself. Thus the third definition is cortical responses under frequency-specific stimulation minus those due to non-frequency specific stimulation. In order to obtain the latter measure, the present study utilized the lowest response of the band (one of the 5 frequency ranges) under stimulation of flickering lights which were not included in that band.Band spectra under flicker and non-flicker conditions are shown in Figs. 4, 5 and 6 and the amount of photic driving in 3 different definitions in Table 3 and that in the 3rd definition in Fig. 6. Photic driving 1 or definition 1 was larger under both EC and MC than under EO and the difference between the first two conditions was negligible. Photic driving 2 was the least under EC for the 3 alpha ranges (bands) and a negative correlation was found between photic driving 2 and either spontaneous alpha responses under EC or the alpha increments from EO to EC conditions. Photic driving 3 was closer in trends to the first definition and mental activity was not effective. The results were explained in terms of the interactions between facilitative and inhibitory effects on alpha responsiveness in addition to its possible upper and lower limits.As was expected, photic driving was quite different between the alpha and beta responses, which would probably indicate different underlying mechanisms.