BS08. Differential effect of flash frequency on cardiac autonomic activity

Introduction Cardiac autonomic activity is susceptible to various stimuli including light. Power spectrum analysis of heart rate variability (HRV) is a method to quantify cardiovascular control. High frequency component (HF) represents cardiac parasympathetic modulation, and the ratio of low frequency component (LF)/HF is associated with cardiac sympathetic modulation. Here we investigated whether intermittent repetitive photic stimulations in different flash frequencies during conventional electroencephalography (EEG) recordings affect heart rate variability (HRV) in normal adults. Methods Data were obtained from 16 normal adult subjects (8 males), age 36.1 ± 12.1 (mean ± SD) years. EEG was recorded with scalp electrodes set in the International 10–20 system. Electrocardiography (ECG) was simultaneously recorded with electrodes set at both hands. Photic stimulation was performed by placing the stroboscope in front of the subjects’ closed eyes. The frequencies of flashes were 3, 6, 8, 10, 12, 14, 16, 18, and 20 Hz, each delivered for 10 s with the pause of 10 s. HRV indices were analyzed by calculating frequency power of 10 s bins shifted by 1.0 s (maximum entropy method, MemCalc, GMS). Results The maximum value of LF, HF, and LF/HF significantly increased as compared to those before the whole train of photic stimulation (LF before 2.5 ± 0.8 log msec 2 , maximum 3.4 ± 0.3 log msec 2 , p  2 , maximum 3.0 ± 0.5 log msec 2 , p  Conclusion The current study suggests that photic stimulations during conventional EEG recordings can significantly increase the cardiac autonomic activity in normal adults. Flash frequency can have differential effects on cardiac parasympathetic and sympathetic modulation.