Nonlinear Phenomena in Neural Networks of the Brain During Monochromatic Sinusoidal Photostimulation

This work presents digital mapping of nonlinear processes in the neural networks of the human brain under different parameters of monochromatic sinusoidal photostimulation. It is shown that during complex bifrequency sinusoidal photostimulation, a nonlinear response is observed in the electrical activity of the cortex. This response manifests as the presence of components in the EEG spectra that are absent from the applied stimuli. These components are both harmonically related to the stimulus and are sums and differences of the stimulus frequencies. New data on the spatial and dynamic features of EEG mappings of nonlinear processes in the brain's neural networks are presented. Based on experimental data, an operational model of EEG response formation is proposed. This model is based on the operation of amplitude modulation (multiplication) of induced rhythms with each other. The products of these multiplications (paraharmonics) are localized in different neural networks, representing independent processes. The operation of rhythm multiplication can be considered a computational process that enables the implementation of various functional systems. Amplitude modulation, i.e., the multiplication of rhythms induced by external harmonic stimulation, may underlie the active nonlinear operations performed by the nervous system during the perception of sensory signals. The role of these nonlinear processes in activating neuroplasticity mechanisms is discussed.