Postnatal Development Of Rat Auditory Cortex Neurons In The Ability Of Detecting Novel Sound Stimulus Frequency

In natural environment,human and animals need to perceive the changes in the environment and respond to them in a timely manner.For animals,the ability to respond to some novel stimuli or events in the surrounding environment is important for them to survive.In the sensory cortex,stimulus-specific adaptation(SSA)refers to the phenomenon that the responses of sensory neurons to novel stimuli(in low probality)are stronger than that to standard stimuli(in high probablity).Although SSA has been extensively studied in the auditory centers of various adult mammals and birds,it is not clear whether the SSA phenomenon exists in the central auditory system of infant and juvenile animals,and if so,whether there are differences in the degree of SSA in the auditory cortical neurons between young animals and adult animals.The aim of the present study was to investigate the SSA in the auditory cortical neurons of rats during different postnatal period,and compare the differences in SSA of auditory cortical neurons among these animals.This study will provide experimental evidence for further understanding of the functional development of central auditory system during postnatal development.This study was conducted on three groups of rats at different postnatal periods:Infant group(P15-20),Juvenile group(P21-30)and Adult group(P64-91).The responses of neurons in the auditory cortex to the oddball sound stimulus sequence were studied in the three groups of rats by using single-neuron electrophysiological recording technique.The results showed that neurons in the auditory cortex exhibited different degrees of SSA at different postnatal periods.The proportions of novelty neurons-in the auditory cortex to detect novel sound stimuli in both infant and juvenile groups were less than that in adult group.The neuronal specific stimulus adaptation index in both infant and juvenile groups were smaller than that in adult group.In addition,the majority of the auditory cortical neurons in the three groups showed a shorter first-spike latency in responding to the novel(or rare)sound stimulus frequency than to the standard stimulus frequency.These results in the present study indicate that a small number of neurons in the primary auditory cortex of the infant rats and the juvenile rats have the ability to detect novel sound stimulus frequency,and there is a developmental process in the novel stimulus detection or SSA in the auditory cortex during postnatal development.