Relations Between Microscopic and Mesoscopic Levels Shown by Calculating Pulse Probability Conditional on EEG Amplitude, Giving the Asymmetric Sigmoid Function

Abstract

The first significant new insight from gamma spatial analysis emerged on re-examination of the sigmoid function representing bilateral saturation. The AM patterns of gamma activity show the capacity of the olfactory system to construct novel responses that are determined by the internal dynamics, and only indirectly by the properties of the stimulus. Therefore, there must exist in the bulb a mechanism by which the input on each inhalation serves to initiate the construction of an AM pattern to be transmitted centrally from the bulb. Most dynamical systems give outputs that are determined by processing of inputs, and that serve as “representations” of the inputs (Freeman 1983; Freeman and Skarda 1985, 1989). We know that for each olfactory burst an input is required, because gamma bursts are prevented by the simple act of closing the nostrils with the fingers to force mouth breathing by awake animals. The most likely mechanism of burst formation is sensitization of the bulb by input, such that the volley of receptor input to the bulb lowers the threshold of certain bulbar neurons to interact among themselves. I concluded that each inhalation might induce an abrupt increase in the feedback gain among bulbar neurons, causing the entire bulb to transit from an equilibrium state under noise during exhalation (Mode 1) to a limit cycle state during inhalation (Mode 2) (Figure IV in Chapter 4).