Properties of repetitive firing in cat motor cortical neurons to membrane depolarizing currents

Abstract

Acute experiments were carried out on immobilized cats under superficial pentobarbital (20 mg/kg) anesthesia to investigate the parameters of the rhythmic discharge of neurons in the motor cortex in the area of representation of the forelimb, evoked by passage of steps of depolarizing current through an intracellular microelectrode. The steady-state repetitive firing rate was found to be a linear function of the strength of the current passing through the membrane; no secondary range was discovered. The slope of the "discharge frequency — current" function (Δf/ΔI=k) was 18±10.7 spikes/sec/nA. The regression line between the slope of the "discharge frequency-current" function and the input resistance (Rin) drawn by the method of least squares had the form k=0.68, Rin=−11.3. Two types of curve of adaptation of the discharge frequency to the stimulating current were found: exponential and undamped oscillations. The curve of latent period of the first action potential in the rhythmic discharge and the length of the first interspike interval as a function of current strength was shown to be a hyperbola, but with different scales along the abscissa. The connection between the properties of the dendritic tree and the parameters of the rhythmic discharge of cortical neurons is discussed.