Effects of Aging and Corticofugal Modulation on Startle Behavior and Auditory Physiology
thesisposted on 10.06.2019, 18:42 by Marisa A Dowling
Frequency-modulated (FM) sweeps play a key role in species specific communication. Evidence from previous studies have shown that central auditory processing has been shown to vary based on the language spoken, which leads to the idea of experience-driven pitch encoding. Other studies have also shown that there is a decrease in this pitch encoding with aging. Using both iterated rippled noise (IRN) and frequency modulated amplitude modulation (FM/AM) methods to create complex pitch sweeps mimicking speech, allows for the processing of pitch to be determined. Neuromodulation using pharmacogenetics allows for the targeted inhibition of a specific neural pathway. Based on previous studies, the primary auditory cortex to inferior colliculus (A1/IC) pathway is hypothesized to be important in pitch encoding. However, there is a lack of evidence on specifically how the pitch information is encoded in the auditory system and how aging impacts the processing. To solve these issues, age-related changes in pitch encoding and maintaining pitch encoding through neuromodulation were characterized in the using behavioral and electrophysiology methods. Behavioral discrimination abilities, measured by modulation of the acoustic startle response, between pitch sweep direction and pitch sweep creation methods highlighted a reduced discrimination in aging and A1/IC inhibited rats. Electrophysiology changes was assessed using envelope-following responses (EFRs) and suggested a decreased initial frequency locking in aging and decrease in frequency locking overall with A1/IC pathway inhibition. Comparison of behavioral and electrophysiology to IRN and FM/AM stimuli show that the decrease in age-related processing as well as A1/IC pathway processing is larger in the behavioral pitch sweep discrimination than in the reduction in EFRs.