The purpose of this study is to measure the representation of stimulus frequencies in the time-patterned responses and the spatial distribution of auditory neurons in the inferior colliculus (IC) of chinchillas. Response areas, representing increases (excitation) and decreases (inhibition) in firing rate relative to spontaneous rate as a function of stimulus frequency and intensity will be constructed for different portions (e.g., onset response and sustained response) of the time-patterned responses to tone-burst stimuli. These experiments will test the hypothesis that response areas are different for specific response components. The spatial distribution of excitation and inhibition will be measured directly by obtaining multi-unit recordings at 100 micron intervals along penetrations normal to the tonotopic axis within the IC central nucleus. It is hypothesized that a tone-burst evokes a focus of excitation at a specific location dependent on stimulus frequency. Furthermore, those neurons that are excited are surrounded by populations of neurons that are inhibited. The computer-controlled protocol will allow collection of the necessary information to detail the size and location of excitatory and inhibitory response as a function of frequency, intensity and time.