The Processing Of Sound Gap Duration By Neurons In The Rat Auditory Cortex Under Monaural And Binaural Conditions

Previous studies have shown that binaural hearing is superior to monaural hearing in accurate sound localization,the segregation and processing of target sound information in a complex acoustic environment,and in understanding speech.The accurate processing of sound temporal information is crucial in the perception and comprehension of human speech,and the processing of animal communication sounds.Previous studies have shown that,unilateral hearing loss significantly degraded the ability of human and animals in processing sound temporal information.However,at present,the correlated neural mechanism at single neuron level is still not clearly understood.The gap detection threshold is often used as an index to evaluate the ability of auditory neurons in sound temporal information processing.Therefore,in the present study,we used the single-unit recording technique to record the responses of rat primary auditory cortex(AI)neurons to sequential sounds with a silent gap between two sound stimuli.We determined the gap detection threshold of each well-isolated single neuron under both monaural and various binaural conditions,and compared the ability of cortical neurons to detect the minimum gap durations between two sound stimuli under these conditions.The results are as follows:The ability of rat primary auditory cortex neurons to detect the gap durations between two sequential sound stimuli was categorized as binaural-advantage,mixed,and monaural-advantage.In the present study,the gap detection thresholds of most cortical neurons determined under binaural conditions were smaller than that determined under monaural conditions,exhibiting the feature of binaural-advantage in detecting sound gap durations.We classified the binaural input of cortical neurons based on their responses to sound stimuli under monaural conditions.The binaural input type of AI neurons was classified as EO if they only responded to stimuli from one ear,but did not respond(or responded very weakly)to stimuli from the other ear.The binaural input type of AI neurons was classified as EE if they responded to sound stimuli from either ear.Our data showed the population of AI neurons in both EE type and EO type exhibited binaural-advantage in detecting sound gap durations.We classified the binaural interaction into three categories according to the neuronal responses to stimuli under both monaural and binaural conditions: facilitatory interaction,inhibitory interaction,and no interaction.The majority of AI neurons within each of the three binaural interaction categories under binaural stimulus conditions showed clearly binaural-advantage in detecting the sound gap durations.The first-spike latencies of rat AI neurons in responding to the first noise-burst in the pair of noise stimuli were relatively stable across gap durations.However,the response latencies to the second noise-burst were shortened with increasing gap durations,and gradually approached to the length of latencies in responding to the first noise-burst.In summary,our results demonstrated that binaural hearing is superior to monaural hearing in the ability of detecting the gap durations between two sequential sound stimuli.The results provide important experimental evidences to help us to understand the mechanism of binaural advantages in processing sound temporal information,and in speech perception in complex acoustic environments.