The Effect Of Temporal And Spectral Processing On Shaping The Rate Selectivity And Direction Selectivity In The Inferior Collicular Neurons

Both animal communication sounds and human speech contain frequency modulations(FM) sweeps.Although modulation rate selective neurons have been found in many kinds of animals at different levels of central auditory structures,the neural mechanism is still an old yet still current topic.By extra-cellular single unit recordings, we examined the neuronal modulation rate selectivity in the inferior colliculus(IC) of Kunming mouse(Mus musculus,Km) in the free-field stimulation conditions.Totally, 102 neurons were recorded,and 41.2%(42/102) of them displayed duration tuning under pure tone(PT) stimulus.Among these neurons,short-pass,band-pass,and long-pass were 22.6%(23/10),8.8%(9/102),9.8%(10/102),respectively.Other 60 neurons(58.8%) didn't show any duration tuning features.Under FM stimulus,the majority of duration tuning neurons(78.6%,33/42) showed rate selectivity.For these neurons,the types of rate selectivity were determined by the duration tuning features,but it had no correlation with the modulation range(MR) of FM.In a small fraction of neurons(14.2%,6/42),the rate selectivity was correlated with the MR while uncorrelated with the duration tuning features.Moreover,the rate or/and duration selectivity of few neurons(7.2%,3/42) was disappeared.In the other hand,more than half of the non-duration tuning neurons(53.3%, 32/60) exhibited the rate selectivity under FM stimulus,and almost all of them(31/32) showed fast-rate selectivity.Nevertheless,there were 8 neurons(8/32) displaying the same best rate at different MR.They were real rate-selective neurons.Our results indicate that modulation rate selectivity to FM sweeps is co-determined by duration tuning features and sweeps bandwidth.There are few rate-selective neurons in the mouse inferior colliculus.Under FM stimuli,there were many neurons showing directional selectivity,35 units (34.3%) showed directional selectivity when the MR and Duration was at 32 kHz and 32 ms,respectively.When MR(or duration) was fixed,the number of directional selectivity units was changed,it increased first then decreased as MR widened or duration increased. There was no relationship between duration tuning and direction selectivity,while DSI increased when duration became longer(P<0.01,One-way ANOVA).In the other hand, the DSI was affected by the relation between MR and RB_10dB,and was also affected by the asymmetry degree of RB_10dB centered by CF,that is,the more significant asymmetry degree,the larger DSI.However,a few neurons showed direction selectivity when MR was narrower than RB_10dB.There were more neurons showed direction selectivity in some combinations of MRs and durations,these MRs and durations leaded to some rates which were consistent with the modulation rate of nature acoustic signal of mice.The results suggest that the directional selectivity is co-shaped by MR and duration in IC neurons of mice.