Studies On The Fine Coticofugal Modulation On Sound Signal Processing Of Inferior Collicular In Hipposideros Pratti

In the auditory system,the inferior colliculus(IC)is a relay station and temporal and spectral information integrations structure under the auditory cortex(AC).It can process and integrate practically all acoustic information inputs from the lower auditory centers or nuclei,contralateral IC and the AC,and then uploads the integrated results to the medial geniculate body(MGB)and AC.These different inputs to IC have different functions.Previous studies found that the auditory signal processing of IC is adjusted or modulated by the corticofugal system.In this study,we used in vivo intracellular recording,focal electric stimulation(ACES)paired with acoustic stimulation to investgate the fine corticofugal auditory information processing modulation of IC neurons in Hipposideros pratti.The main results obtained in the present study are as follows:1.The excitatory and inhibitory corticofugal projections to the IC might shorten and prolong the latency of IC neurons by different mechanisms,respectively.Such as,the excitatory and inhibitory corticofugal projections to the IC might shorten or prolong the response latency of IC neurons through the pre-spike depolarization duration(pre-spike DD),pre-spike hyperpolarization duration(pre-spike HD)and spike onset time(SOT).2.The modulation of AC on the response latency of IC neurons was related to the best frequency(BF)difference between the AC and IC neurons(abbreviated as BFIC-AC difference).The BFIC-AC difference for the corticofugally facilitated IC neurons was significant smaller than that for corticofugally inhibited IC neurons(p<0.05).This indicated that the corticifugal effects were shown to be mediated by widespread inhibition and focused facilitation.3.The responses to the constant frequency(CF)and frequency modulation(FM)component of CF-FM sound(behavior-related acoustic signal)of single-on(SO)and double-on(DO)neurons within the IC of CF-FM bats could be modulated by AC.The facilitatory corticofugal projections from AC to the IC could increase the number of action potentials(APs)(SO,p<0.001;DO,p<0.05)and shorten the response latenies(SO,p<0.05;DO,p<0.05)of SO and DO neurons to the CF component of CF-FM stimulation.By contrast,the inhibitory corticofugal projections from AC to the IC could decrease the number of APs(SO,p<0.001;DO,p<0.01)and prolong the response latenies(SO,p<0.01;DO,p<0.05)of SO and DO neurons to the CF component of CF-FM sound stimulation.And the proportion of corticofugally inhibited SO and DO neurons(SO,33.3%;DO,35.2%)were larger than that of corticofugally facilitated SO and DO neurons(SO,20.8%;DO,23.5%),respectively.Moreover,The BF difference between the corticofugally facilitated SO and DO neurons and the AC neurons was significantly smaller than that of the corticofugally inhibited SO and DO neurons(SO,p<0.05;DO,p<0.05).These are also in good agreement with the characteristic of corticofugal modulation(widespread inhibition and focused facilitation).4.AC has different approaches to modulate the subthreshold responses of SO neurons to the FM component.Among the SO neurons,some part of the SO neurons not only discharged action potentials to CF component,but also showed subthreshold response to FM component of CF-FM sound stimulation.The subthreshold response to FM component was also under the modulation of AC.Moreover,for the subthreshold response to FM component,the proportion of corticofugally inhibited SO neurons(64.7%)were larger than that of corticofugally facilitated SO neurons(23.5%).This suggested that the AC was prone to inhibit the subthreshold response of SO neurons to FM component,which makes the SO neurons only deliver the information from CF component to AC.5.The AC could modulate the response minimum threshold(MT)of DO neurons to the FM component of CF-FM sound stimulation.The excitatory and inhibitory corticofugal projections to the IC could decease(p<0.05)and increase(p<0.05)the MT of DO neurons to the FM component,respectively.Moreover,for the response to FM component,the proportion of corticofugally facilitated SO neurons(52.9%)were larger than that of corticofugally inhibited SO neurons(17.6%).These revealed that the AC mainly enhances the detection ability of DO neurons to the distance and detail informationin the weak echos through decreasing the MT of DO neurons to the FM component.The results and findings revealed that the corticofugal system could exercise fine modulation to the subcortical nuclei.Moreover,the same nature of corticofugal modulation effects could be achieved through different mechanisms,thus ensuring the biologically meaningful sound information uploads to the MGB and AC,and meeting its behavioral needs.