Changes of temporal coding in inferior colliculus and auditory cortex of the guinea pig after cochlear lesion

This project will investigate the changes of temporal coding of neurons in low frequency region of inferior colliculus (IC) and auditory cortex (AC) after damage is created in high frequency region in cochleae (the auditory part of inner ears). Previous studies have suggested that the impact of cochlear lesion is not confined to the auditory peripheral, but extends to central auditory system (CAS) as well. Consequently, plastic changes in the processing of frequency, intensity as well as temporal features of sound have been associated in CAS with sensorineural hearing loss (SNHL). However, a comprehensive understanding in temporal processing problem due to SNHL is not available. Specifically, it is not clear whether and how high-frequency SNHL, the most common pattern of SNHL for the elderly, will produce "off-channel" impact on the temporal processing in the low-frequency region as it has been demonstrated in intensity and frequency coding. This will be the focus of the proposed study. Temporal coding behaviours of IC and AC neurons will be measured in peristimulus time histogram (PSTH), in responses to amplitude modulation (AM) and gaps, as well as in duration tuning. The effect of cochlear lesion will be evaluated in two approaches: (1) by comparing the neuronal responses before and after a short exposure to a traumatizing tone of a high frequency beyond the frequency-response region of the neuron that is under study, (2) by comparing the neurons' temporal coding between normal subjects and those with the chronic cochlear lesion created in high-frequency region by using noise trauma or ototoxic drugs. We will also explore the use of implanted microelectrode to observe the dynamic development of plasticity after a permanent cochlear lesion. In addition, we will investigate the robustness of AM response in IC and AC, the persistence of this response to AM against background noise, the role of local inhibition in this persistence, and finally the potential impact of high-frequency cochlear lesion on this persistence.