Adaptive coherence estimation reveals nonlinear processes in injured brain

Severe injury to the brain may be expected to produce a nonlinear response in evoked potentials (EPs). The authors present a coherence function based method which readily detects an altered brain function resulting from extraneous injury. The coherence function is used to measure the degree of linear association between the EP signals recorded during normal and abnormal experimental conditions. An adaptive coherence estimation algorithm is developed to estimate time-varying model parameters responsive to the brain injury. A linearity index is devised to obtain a single measure of the brain´s departure from linearity. Analyses of somatosensory EP show a very sharp drop in the magnitude coherence estimates during hypoxic injury and a corresponding rapid decline in the linearity index at the very early stages of the hypoxic injury.<>