Date of Graduation


Document Type


Degree Type



School of Medicine


Physiology, Pharmacology & Neuroscience

Committee Chair

Albert Berrebi.


The superior paraolivary nucleus (SPON) is a prominent cell group in the mammalian brainstem. SPON neurons are part of a monaural circuit that encodes temporal sound features in the ascending auditory pathway. Such attributes of acoustic signals are critical for speech perception in humans and likely equally as important in animal communication. While basic properties of SPON neurons have been characterized in some detail, a comprehensive examination of mechanisms that underlie their ability to precisely represent temporal information is lacking. Furthermore, little is known of how the SPON impacts its primary target, the inferior colliculus. Combinations of electrophysiological, pharmacological and histological techniques were used to investigate SPON neuronal responses to stimuli whose temporal parameters were systematically varied. In addition, properties of neurons in the inferior colliculus were examined before and after reversible inactivation of the SPON in order to explore its functional role in hearing. An after-hyperpolarization rebound mechanism was shown to generate the hallmark offset response of SPON neurons in vitro. Single-cell labeling techniques provided a detailed morphological description of cell bodies and dendrites and revealed a homogeneous population of neurons. Moreover, subthreshold ionic currents and synaptic neurotransmitter receptor systems were shown to mediate the precision of responses to temporal features of sound in vivo. It was also demonstrated that input from the SPON shapes response properties of inferior colliculus neurons to both periodic and singular temporal stimulus features. Taken together, these results suggest the SPON likely has a substantial role in temporal processing that has not been taken into account in the current understanding of the central auditory system. Demonstrating a functional role for the SPON in hearing will expand our knowledge of neuronal circuits responsible for representing biologically important sounds in both normal hearing and hearing impaired states.