Spatial separation between two sounds affects the timing of action potentials elicited by the sounds in the rat's auditory midbrain neurons

Abstract

Timing of action potentials (i.e., spikes) elicited by sounds is used by auditory neurons to encode and process acoustic information. In the presence of multiple sounds, the timing of sound-driven spikes is dependent on the temporal, spectral, and spatial relationships among the sounds. We used two tone bursts with different frequencies to form a train of stimuli that were presented at a random odor and a constant rate. Such a train was used to mimic two competing sounds that occurred at the same (50%) probability or a novel sound (i.e., a low probability oddball sound) that was interleaved with a frequently occurring background sound (i.e., a high probability standard sound). We used the rat as an animal model to study how the spatial relationship between two sounds affected the timing of spikes elicited by the sounds in individual neurons in the auditory midbrain. Results indicate that a lower probability of sound presentation led to a higher temporal precision of the timing of the first spike elicited by the sound and the timing could be affected by a spatial separation between two sounds. These results are important for understanding neural mechanisms responsible for hearing in a natural acoustic environment.