Date of Award


Publication Type

Master Thesis

Degree Name



Biological Sciences


Free-field Stimulation, Hearing, Inferior colliculus, Novelty detection, Oddball paradigm, transient neurons


Zhang, Huiming




The ability to detect novel sounds in a natural environment has behavioral significance. For instance, novel sounds are important for predation, predator avoidance as well as inter- and intraspecific communications. One of the methods used to study novelty detection is to record neural responses to oddball paradigm. An oddball paradigm is a train of acoustic stimuli in which an oddball sound (Odd) is occasional and randomly interleaved in an otherwise repetitively presented qualitatively different standard sound (Std). Neurons sensitive to novel sounds exist in auditory structures including the auditory midbrain. This study investigated whether neurons in the auditory midbrain use directional cues in the detection of novel sounds. Two free-field speakers were used to present an oddball paradigm. Meanwhile, action potential discharges were recorded from single neurons in the rat’s auditory midbrain. In reference to the frontal midline of an animal, the two sounds were either co-localized in front of the ear contralateral to the recording site, or spatially separated such that one sound was presented at the contralateral ear while the other sound was presented at a different location in the frontal azimuth. It was found that many IC neurons generated stronger responses to Odd than Std. Neurons with transient firing patterns increased their responses to Odd presented at the contralateral ear when Std in the same sequence of an oddball paradigm was presented at a location that was ipsilateral to the side of recording. In contrast, neurons with sustained firing typically did not change their response to the Odd sound at the contralateral ear regardless of the position of Std in the frontal azimuth. These findings suggest that transient neurons use directional cues to detect novel sounds under natural hearing conditions. The results provide insights into neuronal mechanisms underlying both auditory novelty detection and spatial hearing.