小鼠下丘神经元对不同调制范围的调频声的扫频方向选择性

Effect of frequency-modulated sound with different modulation ranges on sweep-directional selectivity of inferior collicular neurons in mouse

在自由声场刺激条件下,固定调频(frequency-modulated,FM)声的幅度和时程,改变调制范围(modulation range,MR)和扫频方向,记录和测定了小鼠下丘神经元对FM声上、下扫频方向的选择性,探讨了MR对神经元扫频方向选择性的影响.实验共记录到102个神经元,其中45个(44.1%)神经元表现出扫频方向选择性,其余57个(55.9%)神经元则无扫频方向选择性.本实验设置了2,4,8,16和32 kHz 5种不同MR,从2～16 kHz,具有扫频方向选择性的神经元的数目随MR的增加而增加;MR为32 kHz时,有些神经元阈值上10 dB的高、低频边半带宽有不对称的现象,其半带宽越不对称,扫频方向选择性越明显.提示神经元扫频方向选择性的形成与半带宽不对称性有关,由此推测在兴奋性频率反应区内可能有神经抑制的介入,这或许可以对那些MR在神经元频率反应带宽内时仍有扫频方向选择性的特性做出某种解释.

Under free field sound stimulation condition, frequency-modulated （FM） sound of fixed amplitude and duration with 5 modulation ranges （MR）, 2,4,8,16, and 32 kHz, were used in this experiment. The sweep-directional selectivity of the neurons to FM sounds and effect of MR on the sweep-directional selectivity were examined. 45 （44.1%） neurons had sweep-directional selectivity to FM sound and remaining 57 （55.9%） neurons did not have sweep directional selectivity among 102 neurons obtained in this experiment. The number of neurons with sweep-directional selectivity increased with MR increasing from 2 to 16 kHz, but number of neurons with sweep-directional selectivity decreased at MR of 32 kHz, and their half-band widths at 10 dB above minimum threshold （MT） appeared an asymmetry between high and low frequency sides. Half-band widths of these neurons at MR of 32 kHz were more asymmetrical and their sweep-directional selectivity was more remarkable. The result demonstrated that asym- metry of half-band width could affect sweep directional selectivity of the neurons to FM sound and perhaps explain why neurons still had sweep directional selectivity when they were stimulated by MR of FM sound within band width at 10 dB above MT.