Responses of inferior colliculus neurons to sinusoidal amplitude modulation in chinchillas.

摘要

Auditory temporal processing has been investigated throughout the auditory pathway by artificial stimuli such as sinusoidal amplitude modulation (SAM). In this investigation, innovative SAM stimulation was used to reveal several attributes of temporal processing which have not been reported previously in the auditory midbrain. The primary goals of this project were to determine (1) how the modulation depth is represented in the center nucleus of the inferior colliculus (ICc), and (2) how inhibition shapes the response of ICc neurons to modulated sounds.;Responses to SAM stimuli were recorded from single neurons in the ICc of barbiturate-anesthetized chinchillas. Discharge rate (rMTF) and vector strength (tMTF) modulation transfer functions were obtained using different modulation depths. Regions of suppression and regions of enhancement were observed. While the suppression region was common in pauser and sustained neurons, the enhancement region dominated in onset neurons. Comparing the modulation thresholds across different peri-stimulus histogram groups, all pauser and sustained neurons showed modulation thresholds below 40% while all onset neurons showed thresholds above 20%. This suggests that the modulation threshold is mediated by pauser and sustained neurons rather than onset neurons in the ICc.;Responses to SAM tones alone and the presence of steady-state tones were also obtained. The carrier frequency of a SAM tone was either the characteristic frequency (CF) or a frequency in the inhibitory response area (RA). When a SAM tone was presented alone in inhibitory RA, a neuron showed no response or a very weak response to the modulation. However, when a steady-state CF tone was presented simultaneously with the SAM tone, modulated responses were observed. The results suggest that a vast amount of temporal information is carried by inhibitory inputs. The inhibitory stream allows that the temporal comparison across large frequency span occurs at the neuronal level.;The secondary goal of this project was to determine whether anesthetized chinchillas display modulation detection interference (MDI), using a mismatch negativity (MMN) approach. However the signal-to-noise ratio of (MMN) was very low, and large individual discrepancies in response were encountered. It was unrealistic to draw support from the MMN approach to examine MDI in chinchillas.