Characterization of an EPSP-like potential recorded remotely from the round window

The whole-nerve cochlear action potential (CAP), to tone burst stimulation, was recorded before and after application of tetrodotoxin (TTX) to the intact round window (RW) membrane. TTX abolished the CAP leaving a residual negative potential without altering the summating potential (SP) or the cochlear microphonic (CM). The residual potential retained its polarity when recorded from scala vestibuli. The peak latency, amplitude, and tuning properties of the residual potential showed features similar to the CAP. Application of kainic acid to the RW membrane eliminated the residual potential, leaving the SP and CM unaltered. It is hypothesized that the sources of the residual potential are the excitatory post-synaptic potentials from the peripheral processes of afferent dendrites under the inner hair cells.