Fox S E
J Neurophysiol. 1985 Dec;54(6):1578-93. doi: 10.1152/jn.1985.54.6.1578.
If the membrane conductance of a neuron changes, its response to injected current changes. If the change in membrane conductance is restricted to a given subregion of the neuron, that region can be located by analysis of the form of the change in the response of the neuron to current injection. The theoretical basis of this method is rigorously developed in this paper. Location of the membrane conductance change is possible because the higher-frequency components of the injected currents are progressively attenuated by the axial resistance and membrane capacitance of the neuron as they pass from the injection site to electrotonically more distant regions. For the lower-frequency components, this attenuation is less pronounced. Therefore, when a conductance change occurs relatively far from the recording/current-passing electrode, only the lower frequency components of the response are altered, because the higher-frequency components of the current do not even reach that site. When such a conductance change occurs relatively near the electrode, both the lower and the higher frequency components of the response are altered. Treating the neuron as a passive network, the input impedance at a given frequency is simply the voltage response of the neuron at that frequency divided by the current injected at that frequency. This is a complex value, having both magnitude and phase components. The change in the magnitude of the input impedance due to a conductance change occurring distally drops off more rapidly with increasing frequency than that due to a proximal conductance change. In addition, for distal conductance increases the magnitude of the input impedance can increase in the higher range of frequencies. This paradoxical effect is treated in APPENDIX I. For many neurons an estimate of the electrotonic location of a conductance change can be made knowing only the change in input resistance, the change in the magnitude of the input impedance at the characteristic frequency (omega 0 = 1/tau 0), and a reasonable estimate of the total electrotonic length of the neuron (L). The sensitivity of the method depends on the electrotonic length of the neuron. The method is most useful in neurons with dendritic trees longer than approximately 0.5 length constants. The dendritic-to-somatic conductance ratio of the neuron does not appreciably affect the forms of the responses. The time constant merely shifts the frequency range of interest.(ABSTRACT TRUNCATED AT 400 WORDS)
如果神经元的膜电导发生变化，其对注入电流的响应也会改变。如果膜电导的变化局限于神经元的特定子区域，那么通过分析神经元对电流注入的响应变化形式，就可以确定该区域的位置。本文严格阐述了该方法的理论基础。能够确定膜电导变化的位置是因为注入电流的高频成分在从注入部位传递到电紧张性更远的区域时，会被神经元的轴向电阻和膜电容逐渐衰减。对于低频成分，这种衰减不太明显。因此，当电导变化发生在离记录/通电极相对较远的位置时，只有响应的低频成分会改变，因为电流的高频成分甚至都无法到达该部位。当这种电导变化发生在离电极相对较近的位置时，响应的低频和高频成分都会改变。将神经元视为一个无源网络，给定频率下的输入阻抗就是该频率下神经元的电压响应除以该频率下注入的电流。这是一个复数值，有幅度和相位分量。由于远端电导变化导致的输入阻抗幅度变化随频率增加而比近端电导变化导致的下降得更快。此外，对于远端电导增加，输入阻抗的幅度在较高频率范围内可能会增加。附录I中讨论了这种矛盾效应。对于许多神经元，仅知道输入电阻的变化、特征频率（ω0 = 1/τ0）下输入阻抗幅度的变化以及对神经元总电紧张长度（L）的合理估计，就可以对电导变化的电紧张位置进行估计。该方法的灵敏度取决于神经元的电紧张长度。该方法在树突树长于约0.5个长度常数的神经元中最有用。神经元的树突与胞体电导比不会明显影响响应的形式。时间常数只是改变了感兴趣的频率范围。（摘要截于400字）
