An alternative methodology for the estimation of frequency changes in electroencephalogram signals

We present a novel methodology based on communication systems, able to track frequency changes in biosignals. The proposed approach is based on a phase lock loop (PLL) circuit and includes subcomponents that allow the estimation of frequency variations. The proposed system can be modeled as a second-order control system, enabling a strait forward definition of its parameters. We found that depending on the initial frequency of the voltage-controlled oscillator (VCO) the PLL tracks different frequency components, allowing assessing the range of frequencies that changes and how they change, leading to the development of time-frequency maps. The new approach was tested in Electroencephalogram (EEG) signals collected from patients subjected to general anesthesia. The developed methodology is available online as a demonstration tool for students from the Master on Biomedical Engineering at University of Coimbra. The system is didactic in two ways: it demonstrates how a second order control systems works, and how frequency variations in the time-frequency domain are computed and their importance.