ABSTRACT
This chapter deals with the properties of oscillatory neural delayed feedback systems and focuses in particular on the human pupil light reflex (PLR). It describes experiments designed to induce oscillatory neural activity in the human PLR. The chapter outlines a model used to study autonomous oscillations in the human PLR. Nonlinear dynamics deals with the study of periodic and aperiodic oscillations. Most studies involve either modeling or computation from time series of dynamical invariants such as the fractal dimension or Lyapunov spectrum. The chapter also describes the Hopf bifurcation in ordinary and delay-differential equations. The chapter also deals with the stochastic Hopf bifurcation in delay differential equations (DDE) and the concept of physiological order parameter. It discusses physiological irregularity. The debate has centered on whether chaos, noise, or both underlie the irregularity. More stringent and self-consistent tests for chaos, based on prediction of time series, are being developed and hold hope for clarifying the source(s) of irregularity.
