[Relationship between the changes of spontaneous activity and responses of cortical neurons under microiontophoretic...

In neurons of the gyrus sigmoideus posterior of cats, the influence of microiontophoretic application of varying doses of glutamic acid upon the reaction of those neurons to stimulations of the ischiadic nerve and clicks, and the changes of spontaneous activity were studied. The application of glutamic acid led, in 97% of the 90 neurons studied, to a dose-dependent increase in the mean firing rate; in 34% of neurons, to effectuation of click responses, and affected the reaction to stimulation of the ischiadic nerve to a varying extent. With increasing doses of glutamic acid, there was a linear correlation between the logarithm of spontaneous activity and the activity of excitatory responses with considerable differences in the steepness of the resulting straight lines for the individual neurons.