Environmental Enrichment Induces Plasticity Of Directional Selectivity Of Auditory Cortex Neurons In Rats During The Early Postnatal Period

Conventional electrophysiological techniques were applied to study the effect of the environmental enrichment on the directional selectivity of the primary auditory cortex neurons in rats.The auditory response properties of the single neuron were used as the index in this experiment.1.The effect of the environmental enrichment on the directional selectivity of the primary auditory cortex neurons of the rats which reared in the environmental enrichment during the early postnatal periodA total of 26 rats were used in this part,divided into EE1(n=13) and CON1(n=13) groups.EE1 rats were housed in environmental enrichment during the early postnatal period until eight weeks.The CON1 rats housed in standard conditions after birth were used as age-matched controls.It was found that the proportion of the azimuth-selective neurons of the EE1 group increased significantly compared with the CON1 group,whereas the proportions of the multi-peak,hemi-field and non-selective neurons decreased significantly.For both groups,the distributions of the best azimuth(BAz) of auditory neurons were concentrated and mostly located in contralateral auditory space,especially from contralateral 15°to 54°.But the EE1 had more enhanced distribution in 25°～44°than the CON1 group.Linear regression analysis between the BAz and characteristic frequency(CF) showed that BAz significantly increased with decreasing CF in both groups.However,The correlation coefficients(r) indicated the BAz of the EE1 group was more significantly correlated with the CF compared with the CON1 group and there was a significant difference between the correlation coefficients of the two groups(p＜0.05).The average of azimuth range(ARs) of the EE1 group was significantly smaller than that of the CON1 group(p＜0.001),and this difference was particularly significant for the central three regions(15°～44°).In addition,the average AR gradually decreased with CF increasing for both groups,and the differences were significant between the EE1 and CON1 groups for all three CF categories,especially in the 9.5～30kHz frequency of CF category(p＜0.001).These results showed that rearing in environmental enrichment during the early postnatal period after birth could induce the plasticity of the directional selectivity of the auditory cortex neurons in rats.It could significantly improve the directional selectivity of the auditory cortex neurons.2.The directional selectivity of the auditory cortex neurons of the rats which reared in the environmental enrichment after the critical periodA total of 20 rats were used in this part,divided into EE2(n=10) and CON2(n=10) groups.The EE2 rats were reared in environmental enrichment after critical period until 16 weeks.The CON2 rats housed in standard conditions after birth were used as age-matched controls.The results showed that there was no significant difference of the proportion of the azimuth-selective neurons between the two groups.The distribution tendencies of the BAz in horizontal direction of the two groups were nearly the same.Linear regression analysis between the BAz and CF showed that BAz significantly increased with decreasing CF in both groups and there was no significant difference between the correlation coefficients of the two groups(p＞0.05).In addition,there was no significant difference of the average ARs between the EE2 and CON2 groups and had no significant difference in all BAz regions.We found that the average AR gradually decreased with CF increasing for both groups,but there was no differences between the EE1 and CON1 groups for all three CF categories(p＞0.05).These results indicated that the inducement of the environment in the plasticity of the auditory functional development correlated with the age of the animals.It could not induce the developmental plasticity of the directional selectivity of the auditory cortex neurons in rats which reared in environmental enrichment after the critical period.