The ensemble background activity (EBA) recorded from the round window has a spectral peak near 900 Hz that is generally attributed to spontaneous eighth-nerve activity, but other frequency regions are less well understood, including the issue of contribution of hair cell (HC) potentials. To further investigate the EBA, an intracochlear electrode pair was employed to record from the basal turn in guinea pig, applying the principles of differential recording. Results confirmed 900 Hz to be the dominant feature of the EBA power spectrum in/near quiet, wherein this peak was more robust in the average derivation and readily suppressed by kainic acid, consistent with its presumptive neural origin. Another broad spectral prominence, centered around 3000 Hz, was more prominent in the difference derivation, dominated the spectrum with increasing external (white) noise, and was much less sensitive to kainic acid, implying a predominantly HC origin. The findings demonstrate efficacy of intracochlear EBA recording, potentially extend EBA utility via the differential recording method, and further validate the EBA for monitoring spontaneous activity of the eighth nerve.

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