猫外膝体神经元对正弦调制光刺激反应的线性和非线性特性

用不同频率正弦波调制发光二极管亮度,刺激猫外膝体细胞的感受野中心。用Apple-Ⅱplus 计算机将细胞放电频率的瞬时变化作成反应直方图(PSTH)。通过傅里叶变换,计算平均放电率、基波幅度和高次谐波幅度的变化,定量地研究了细胞反应的线性和非线性性质。 1.在恒定的平均亮度下,持续细胞的反应具有较好的线性特征,表现在PSTH可以重现正弦光刺激的频率和波形;与此相反,瞬变细胞的反应显示明显的非线性性质,PSTH出现半波整流波形,反应上升相交陡而下降相较平缓。 2.两类细胞对正弦刺激的反应具有不同的谐波成分:典型持续细胞的反应中主要包含基波成分,高次谐波的幅度接近噪声水平;但是,瞬变细胞的谐波可以延续到8次之多,二次和三次谐波的幅度可高达基波幅度的50％。 3.逐渐增加调制光刺激的平均亮度,持续细胞反应中二次谐波幅度始终保持在很低的水平上,而瞬变细胞的谐波幅度则随着增大。 4.增加光刺激的调制深度,持续细胞的反应特点是:(1)平均放电率保持不变或略有增加,(2)二次谐波增长很慢,(3)基频相位基本保持不变。与此相反,瞬变细胞的平均放电率和二次谐波幅度都随调制深度增加而明显地增大,并且基波相位也可见到较明显的前移。 以上结果表明,持续细胞与瞬变细胞在时间域方面也具有线性和非线性的差别。

LINEAR AND NON-LINEAR PROPERTIES OF CAT LGN NEURONE RESPONSES TO SINUSOIDAL LIGHT STIMULATION

The receptive field center of LGN neurones of cat was stimulated by light emit-ing diode, the luminance of which was modulated sinusoidally at various temporalfrequencies. Peristimulus time histograms (PSTH) were constructed by an Apple-II plus computer. The mean discharge rate, amplitudes of fundamental and higherharmonic components with regard to their linear and non-linear properties werestudied quantitatively. 1. Under constant luminance, the response property of sustained cells waslinear in so far as their discharge frequencies reproduced the wave form of sinusoi-dal light stimulation faithfully. On the contrary, non-linearity of transient cellswas clearly shown in the PSTH by the appearence of half-wave rectification witha steeper rising and a slower falling phase. 2. The two types of cells responded to sine wave stimulation with differentharmonic components. Responses of typical sustained cells consisted principallyof the first harmonic (fundamental) with negligible higher order components. Butin transient cells, components up to 8th harmonics were found, and the second andthe third might reach an amplitude as high as 50% of the fundamental. 3. By systematically increasing the mean luminance of modulated light stimu-lation, the second harmonic in sustained cells was maintained at a rather low level.In contrast with this, a gradual increase of harmonic amplitude was seen in transienLcells. 4. When the modulation depth of light stimulus was increased, the responsesof sustained cells are characterized by (i) constant or very slight increase of the meandischarge rate, (ii) very slow increase of the second harmonic component and (iii)practically no change of phase of the fundamental component. In transient cells,on the contrary, marked increase of the mean discharge rate and the second harmonicand significant forward shift of the fundamental phase were observed. The results showed that sustained and transient cells could be differentiatedfrom each other by their linear and non-linear properties in the temporal domain.