Linear approximation of prepyriform evoked potential in cats

Abstract

Electrodes were implanted in six cats for stimulation of the lateral olfactory tract with pulses of constant amplitude and duration, and for recording from the primary olfactory cortex. Wave forms of single-shock evoked potentials (time-response curves) were determined with an average response computer. Frequency-response curves were constructed by plotting mean absolute amplitude of evoked potential against stimulus rate. These results were analyzed in terms of a linear second-order differential equation simulated by an analog computer. Reconstruction of the evoked potential required driving the computer with single pulses, differentiating the damped sinusoidal output with an RC-network, and mixing response frequencies having one to three discrete means and a normal distribution about each mean. Reconstruction of the frequency-response curves required use of the same stimulation and recording devices used on the animals, plus differentiation and distribution of the output, plus addition of “spontaneous” or intercurrent activity. In occasional instances the evoked potential could be closely approximated by a simple exponentially decaying cosine wave. The majority of wave forms displayed varying degrees of distortion from that pattern, with stable individual differences among cats. Such differences could be simulated by mixing of component frequencies, which were identified from peaks in the frequency-response curves. It was concluded that, for constant amplitudes of impulse driving less than 1.5 × threshold, any electrical response of this cortex in the waking cat could be approximated by a linear second-order equation, to such an extent that specification of frequency spectrum, phase of onset, amplitude, and Q would describe that response.