MICROELECTRODE STUDIES OF NEURAL AUDITORY ACTIVITY OF CAT. II. MEDIAL GENICULATE BODY

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Abstract
Electrical recordings were made from the medial geniculate body, using chiefly microelectrodes; larger monopolar electrodes were used for comparison. Neural elements in the medial geniculate body were found which would respond continuously with spike discharge to continuous tonal stimulation. These elements showed specificity of function, since they were maximally sensitive to particular frequencies. Variations in rate of fire with intensity and duration of stimulation have been described. Latency of spike discharge to tonal onset stimulus and clikc stimulus was near 9-10 msec. on the average at the highest intensities of stimulation used. Large wave response to tonal onset and click stimuli appeared oc-casionally in addition to spike response, when recording with microelectrodes, and usually consisted of a negative wave with no preceding positive wave. Increases occurring in these responses with increase in intensity of tone and click stimuli have been described, both for microelectrode and larger mono-polar electrode recording. The latency of the negative wave at highest intensities of stimulation tended to be near 9 msec, whereas the latency of the large positive wave recorded with larger monopolar electrodes was found to be close to 5 msec. Masking of neural response to pure tones by pure tones and thermal noise was demonstrated. Neural response to clicks could also be masked. Click response was best masked by frequencies in the region of those which produced best neural response for a given electrode placement. These results add to the evidence for localization of response in the auditory system according to stimulating frequency.