Neural processing of novel sounds in the rat’s inferior colliculus

Abstract

A novel sound is an occasionally occurring acoustic event in a constant/repetitive acoustic environment. Auditory neurons display sensitivity to a novel sound by reducing action potential discharges over repetitive acoustic stimulation and restoring discharges upon presence of a novel sound. We used the rat as an animal model and conducted in vivo neurophysiological recordings to examine how novel sounds are processed in the midbrain auditory structure, the inferior colliculus (IC). The IC receives convergent inputs from structures including those with neurons sensitive to novel sounds. These inputs have diverse sensitivities to temporal, spectral, and directional acoustic cues and produce excitatory/inhibitory synaptic events with different time courses in IC neurons. Integration among these inputs in IC neurons provides a likely physiological basis for processing the novelty of a sound and other dynamic acoustic characteristics. We used both closed- and free-field stimuli to examine responses to oddball paradigms. Our results indicate that neurons sensitive to novel sounds existed in the IC. These neurons typically have onset firing patterns; and their sensitivity to a novel sound is affected by the spatial relationship between the novel sound and a repetitive standard sound in the environment. [Research supported by NSERC of Canada.]