State-dependent modulation of thalamocortical oscillations by gamma light flicker with different frequencies, intensities, and duty cycles

Abstract

Rhythmic light flickers have emerged as useful tools to modulate cognition and rescue pathological oscillations related to neurological disorders by entrainment. However, a mechanistic understanding of the entrainment for different brain oscillatory states and light flicker parameters is lacking. To address this issue, we proposed a biophysical neural network model for thalamocortical oscillations (TCOs) and explored the stimulation effects depending on the thalamocortical oscillatory states and stimulation parameters (frequency, intensity, and duty cycle) using the proposed model and electrophysiology experiments. The proposed model generated alpha, beta, and gamma oscillatory states (with main oscillation frequences at 9, 25, and 35 Hz, respectively), which were successfully transmitted from the thalamus to the cortex. By applying light flicker stimulation, we found that the entrainment was state-dependent and it was more prone to induce entrainment if the flicker perturbation frequency was closer to the endogenous oscillatory frequency. In addition, endogenous oscillation would be accelerated, whereas low-frequency oscillatory power would be suppressed by gamma (30–50 Hz) flickers. Notably, the effects of intensity and duty cycle on entrainment were complex; a high intensity of light flicker did not mean high entrainment possibility, and duty cycles below 50% could induce entrainment easier than those above 50%. Further, we observed entrainment discontinuity during gamma flicker stimulations with different frequencies, attributable to the non-linear characteristics of the network oscillations. These results provide support for the experimental design and clinical applications of the modulation of TCOs by gamma (30–50 Hz) light flicker.

Visual light flicker stimulation: enhancing alertness in sleep-deprived rats

“…Notably, gamma rhythmic light flicker (either 40 Hz or 60 Hz) has been shown to non-invasively synchronize cortical gamma neural oscillations, potentially enhancing cognitive functions, such as learning and memory, thereby revealing the therapeutic promise of flicker stimuli ( Singer et al, 2018 ; Yao et al, 2020 ; Lin et al, 2021 ; Venturino et al, 2021 ). Although exposure to light generally suppresses alpha, theta, and other lower-frequency neural activities—markers of drowsiness ( Yokoi et al, 2003 ; Vandewalle et al, 2009 ; Wang et al, 2022 ), the specific impact of visual flicker stimuli on central fatigue and entrainment effects is less understood. Moreover, light influences fatigue and drowsiness via circadian rhythm mechanisms integral to our biological clock ( Wong and Fernandez, 2021 ).…”