Directional Sensitivity And Corticofugal Modulation Of The Mouse Inferior Collicular Neurons

Sound location is the main function of the hearing system.As the important nuclear of the central hearing system in mammal.Inferior colliculus takes part in processing the spatial information.Conventional electrophysiological technique is used to determine the tuning properties and corticofugal modulation of the mouse inferior colliculus in free-field conditions.These findings provide evidence for further study of spatial coding mechanisms and corticofugal modulation mechanisms of central auditory information process.1.Auditory spatial response properties of the mouse inferior collicular neuronsConventional electrophysiological technique was used to determine tuning properties and possible mechanism of the mouse inferior collicular(IC)neurons against different directional sound stimulation under free- field condition.Among 258 IC neurons we studied,the characteristic frequencies(CFs)of most IC neurons distributed from 8 kHz to 20 kHz along dorsal-ventral axis which showed tonotopic organization of central nucleus of the IC.Furthermore,the distribution of best azimuth(BAz)of IC neurons was concentrated and most of them(85.8%)located in contralateral auditory space,especially from contralateral 20°to 50°.The relationship between the BAz of IC neurons and their CFs appeared significant correlation,which showed that the BAz of these IC neurons increased with their CFs. According to the properties of the directional sensitivity curves,these neurons can be divided into four tuning modes:Azimuth-selective(84.8%);Hemi-field(11.4%); Multi-peak(2.3%);Non-selective(1.5%).The results showed that IC neurons had obvious directional sensitivity and good expression against directional azimuth.They can detect different sound location from frontal field because of variety of directional sensitivity properties.It also showed sound information was processed in inferior colliculus.These findings provide evidence for further study of spatial coding mechanisms of IC neurons.2.Corticofugal modulation of directional sensitivity in the mouse inferior collicular neuronsUsing conventional electrophysiological technique,we investigated the corticofugal modulation of the directional sensitivity of mouse inferior colliculus(IC). Among 81 IC neurons we studied,after cortical electrical stimulation,44.9%Azimuth range(AR)of IC neurons narrowed,showing the effect of inhibition,while 42.0% widened,showing the effect of facilitation.The change of most AR(34/60,56.7%) concentrated on the range of±5°and the CF_IC-CF_ACrange of±5°kHz.When the CF of auditory cortical neurons was larger than the CF of IC neurons,the ratio of AR change was bigger after cortical electrical stimulation.At the same time,we investigated that after cortical electrical stimulation,most best azimuth(BAz)of IC neurons had shifted,including shift-left(30.9%)and shift-right(28.4%).The shift of most BAz concentrated on the range of±10°and the CF_IC-CF_AC,c range of±5°kHz..When the CF of auditory cortical neurons was larger than the CF of IC neurons, the ratio of AR change was bigger after cortical electrical stimulation.The results indicated that auditory cortex played an important part in the modulation of directional information.These findings provided evidence for further study of corticofugal modulation mechanisms of central auditory information process.