Field potentials in rat brain stem during binaural acoustic stimulation

Abstract

Electric field potentials were measured in rat brain stem while presenting monaural or binaural acoustic click stimuli. The binaural difference (BD) potential, defined as the sum of field potentials due to menaural stimuli minus that due to a binaural stimulus, was recorded at 1-mm intervals along a track passing through the inferior colliculus and the superior olivary nuclei. Scalp surface potentials were recorded simultaneously. Prominent BD potentials were observed at all intracranial locations. Scalp surface BD was contemporaneous with an intracranial BD waveform that reversed sign at a level midway between the inferior colliculus and the olivary nuclei. The onset of BD potentials at or below this level occurs 1 ms after the appearance of prominent monaural and binaural response waveforms. This latency difference suggests the existence of an additional synapse in the pathway leading to the structure responsible for BD generation compared to pathways leading to other structures in the superior olivary complex. [Work supported by Penn Lions Hearing Research Foundation.]