Electric Responses of Individual Nerve Ele- Ments in Cochlear Nucleus to Sound Stimulation

IN A RECENT PAPER one of us (7) described the technique and the results of recording impulses from individual auditory nerve fibers in the modiolus of the guinea pig. The present investigation is an extension to the cochlear nucleus in the medulla oblongata of the same technique of recording action potentials with submicroscopic microelectrodes (6). Action potentials from single elements in the cochlear nucleus have already been successfully recorded by Galambos and Davis (2, 3, 4) with an earlier type of microelectrode. The original purpose of the present investigation was to repeat their previous observations with a finer technique. There is a certain difference in behavior between the elements examined in the present investigation and those studied previously. The “response area” of an element is the area on an intensity-frequency plot that includes all tones that evoke a positive response. The response areas of the new elements show a sharp limit on the high-frequency side and very gradual elevation of threshold on the low-frequency side. The elements studied previously had, on the contrary, fairly narrow response areas with a clear maximum of sensitivity for a certain frequency that was characteristic of the element under observation. The new and the previous elements behaved differently in one other aspect: spontaneous discharges of impulses in the new elements were not inhibited by the application of any pure tone, while in the previous elements some tones inhibited and other tones enhanced the spontaneous repetitive activity.