Modulation Of Auditory Information Processing In Central Neurons

1.Modulation of electrical stimulation to medial prefrontal cortex on the acoustically evoked responses of auditory cortical neurons in ratsConventional electrophysiological technique was used to investigate the modulation of electrical stimulation to medial prefrontal cortex(mPFC)on the acoustically evoked responses of auditory cortical(AC)neurons in 60 rats.Among 122 AC neurons isolated, the influences of mPFC on the acoustically evoked responses of 93 AC neurons were investigated systematically.20(21.5%)neurons were not affected,but the acoustically evoked responses of the remaining(73 neurons,78.5%)were either facilitated(39 neurons,41.9%)or inhibited(34 neurons,36.6%).The degree of facilitation and inhibition in the acoustically evoked responses was dependent upon the time intervals between acoustic and electrical stimuli.The best intervals of facilitation and inhibition were between 5 and 30 ms(mostly 10 and 15 ms).Our findings suggested that the mPFC may affect the activity of AC neurons through different multi-synaptic pathways.2.Modulation of electrical stimulation to mPFC on frequency RF plasticity of AC neurons in rats(1)Modulative Type of frequency RF plasticity of AC neurons by ES-mPFCUsing conventional electrophysiological technique,we investigated the modulation of electrical stimulating of mPFC(ES-mPFC)on frequency RF plasticity of 226 AC neurons in rats.When mPFC was electrically stimulated,the RF plasticity of 55(24.3%)neurons were not affected,but RF plasticity of the remaining(171 neurons,75.7%)were either inhibited(64 neurons,37.4%)or facilitated(80 neurons,46.8%).The modulation on RF plasticity has three types:the inhibitory type,the facilitatory type and the uncertain effect type(27 neurons,15.8%).The inhibitory type of mPFC modulation lengthened RF shifting time course and shortened RF recovery time course.Conversely,the facilitatory type of mPFC modulation shortened RF shifting time course and lengthened RF recovery time course of AC neurons.The uncertain type of mPFC modulation lengthened or shortened both RF shifting time course and recovery time course.Our findings suggested that the mPFC may affect the plasticity of functional activity of AC neurons through different multi-synaptic pathways,and also may participate in the process of learning and memory.(2)Modulation of mPFC on frequency RF plasticity direction of AC neurons and modulation limitationWhen mPFC was electrically stimulated,the RF shift could be induced by the frequency which was either higher or lower than the control BF,demonstrating no clear directional preference.The frequency RF of some neurons showed bidirectional shifts, and the RF of other neurons showed single directional shift.This result was similar to our work of RF shifting direction finished previously.After ES-mPFC,the probability of the RF complete shift was slightly enhanced,however,which could not change the scope and direction of RF shift.(3)Modulation on RF plasticity by deactivating mPFC(DS-mPFC)We investigated the RF plasticity by micro-injecting procaine to ES-modulative spots in mPFC.The results indicated that the modulative effects of 21 facilitatory type neurons and 6 inhibitory type neurons were canceled after procaine DS-mPFC,while the modulative effects of 13 neurons could not be canceled completely by procaine DS-mPFC.In some neurons,we studied the DS-mPFC effect on spontaneous impulses of AC neurons.The result showed that DS-mPFC increased the level of spontaneous impulses of AC neurons.It suggested that rat mPFC might play an inhibitory role in information processing of inferior cortical areas in natural condition,which could be canceled by procaine DS-mPFC.3.Modulation of AC on directional sensitivity in the midbrain inferior collicular neurons of Kunming mice,Mus musculus Km (1)Auditory spatial response properties of midbrain inferior collicular neuronsAuditory spatial response properties of 138 inferior collicular(IC)neurons of mouse, Mus musculus Km,were studied using electrophysiological method under free-field conditions.The results showed that the best frequencies(BFs)of most IC neurons distributed between 10 kHz and 25 kHz along dorsal-ventral axis,which showed tonotopic organization of central nucleus of the inferior colliculus.Furthermore,the distribution of best azimuth(BAZ)of IC neurons was concentrated and most of them (87.7%)located within 20°-50°contralateral in azimuth of the frontal auditory space. The relationship between the BAZ of IC neurons arid their BFs appeared significant correlation,which showed that the BAZ of these IC neurons increased with their BFs.It suggested that midbrain IC neurons have significant directional sensitivity.(2)Modulation of AC on acoustically evoked responses in the midbrain IC neuronsWe evaluated the modulation of mouse AC on the acoustically evoked responses of 80 IC neurons by electrical stimulation.When AC was electrically stimulated,75 neurons were facilitated(24 neurons,30%)or inhibited(51 neurons,63.75%).The modulation of AC on the acoustically evoked responses of 63 IC neurons was investigated systematically.The degree of facilitation and inhibition in the acoustically evoked responses was dependent upon the time intervals between acoustic and electrical stimuli and electric current intensity.The best intervals of facilitation and inhibition were between 3 and 5 ms in most IC neurons(more than 74%).The best electric current intensity were between 18 and 26μA in most IC neurons(more than 75%).(3)Modulation of AC on directional sensitivity in the midbrain IC neuronsUsing conventional electrophysiological technique,we investigated the modulation of AC on directional sensitivity of 86 IC neurons by electrical stimulation under free-field conditions.Our results showed that IC neurons can be mainly divided into to two groups concerned with their directional sensitivity(DS).GroupⅠ,cortical electrical stimulation shifts the best azimuth(BAZ)of IC neurons(45,52.3%);GroupⅡ,cortical electrical stimulation does not shift the BAZ of IC neurons(41,47.7%).In groupⅠ,DS curves of 19 neurons were recorded completely before and after AC was electrically stimulated.IC neuron with an increasing AR after ES-AC were called asⅠa neuron(11/19);while those with a decreasing AR after ES-AC were called asⅠb neuron(8/19).In groupⅡ, DS curves of 31 neurons were recorded completely before and after AC was electrically stimulated.,includingⅡa neurons(15/31,increased AR after ES-AC)andⅡb neurons (16/31,decreased AR).The results indicated that auditory cortex has modulation on directional sensitivity in the midbrain IC neurons.