Frequency And Spatial Coding Of Auditory Information In Auditory Cortex And Inferior Colliculus

Frequency and spatial coding of auditory information in auditory cortex and inferior colliculus was studied in this research. We found that AC stimulation narrowed the excitatory FTCs and asymmetrically expanded the lateral inhibitory FTCs of corticofugally inhibited ICc neurons. The opposite results were observed for excitatory and inhibitory FTCs of corticofugally facilitated ICc neurons. Corticofugal inhibition increased sharpness, minimum threshold, and decreased the frequency-intensity response area of EFTCs, at the same time it decreased the sharpness, minimum threshold but increased the frequency-intensity response area of IFTCs. The opposite results were observed for EFTCs and IFTCs of corticofugally facilitated inferior collicular neurons. During corticofugal inhibition, the percent change of frequency-intensity response area of EFTCs had significant correlation with the percent change of that of IFTCs. These data suggest that cortical neurons are likely to improve frequency information processing of inferior collicular neurons by modulation of IFTCs. We also demonstrated that one corticofugai pathway is that auditory cortex sends excitatory inputs to ICX and then sends inhibitory inputs to ICC from ICX.Under free field sound stimulation conditions, we studied the sound direction effect on frequency tuning curves of inferior collicular (IC) neurons. This study showed that the MT and sharpness of frequency tuning curves increased as the sound direction changed from contralateral to ipsilateral azimuthal angles. It suggests that sound direction effect on frequency tuning may be through the complex interplay between the excitatory and inhibitory inputs. The application of GABA(A) antagonist, bicuculline, lowered all MTs but the application did not abolish direction-dependent variation in MT. In contrast, although application of bicuculline essentially had no effect on the BFs of IC neurons, it differentially broadened neurons FTCs at different azimuths abolishing the direction-dependent sharpening of frequency tuning. These data indicate that GABAergic inhibition makes an important contribution to the direction-dependent frequency tuning of most IC neurons. Corticofugal modulation of the excitatory and inhibitory FTCs of most IC neurons was more pronounced at one sound direction than the other. Sound direction effects on frequency tuning characteristics may undergo a postnatal development due to the development of excitation and inhibition integration.In this study, we also examined the Sound stimulation activates C-Fos expression in auditoryCorticofugal regulation of excitatory and inhibitory frequency tuning curves of bat inferior collicular neurons Brain Res 1999 Sep ll;841(l-2): 184-188Corticofugal regulation of excitatory and inhibitory frequency tuning curves (FTCs) of neurons in the central nucleus of bat inferior colliculus (ICc) was studied by electrical stimulation of the primary auditory cortex (AC stimulation) under free field stimulation conditions using a two-tone inhibition paradigm. AC stimulation narrowed the excitatory FTCs and asymmetrically expanded the lateral inhibitory FTCs of corticofugally inhibited ICc neurons. The opposite results were observed for excitatory and inhibitory FTCs of corticofugally facilitated ICc neurons. These data support previous reports that corticofugal systems work together with widespread lateral inhibition to regulate subcortical frequency processing.Corticofugal Modulation of Frequency Tuning of Inferior Collicular Neurons in Big Brown Bat, Eptesicus Fuse us Chinese Science Bulletin, 2000In order to explore the possible mechanism of corticofugal modulation of excitatory frequency tuning curves (EFTCs) of midbrain neurons, we examine the change of sharpness, frequency-intensity response area, minimum threshold of both EFTCs and inhibitory frequency tuning curves (IFTCs) of inferior coliicular neurons during corticofugal modulation using two-tone inhibition paradigm and micro-electrical stimulation technique. Our data showed that...