Capacitance compensation and bridge balance adjustment in intracellular recording from dendritic neurons

Under most experimental conditions in intracellular recording, the proper adjustment of the amplifier is essential for the interpretation of the signals recorded from neurons. It is considered possible to accurately align the capacitance compensation and bridge balance adjustments of the amplifier simultaneously with the recording of membrane potential of an impaled cell if a number of conditions are met. In the strictest sense, these conditions are met only if: (1) the neuron is isopotential and if its electrical behavior can be adequately described using a single exponential decay constant, and if (2) that decay time constant is much longer than that of the microelectrode. These conditions cannot usually be satisfied. Because intracellular adjustment of capacitance compensation and bridge balance is necessary in many circumstances, it is desirable, to know whether any of the methods for performing these adjustments are accurate when used under less strict constraints, and to assess the nature and degree of the error that can be expected when the constraints are ignored. The results of computer simulations of a simple intracellular recording amplifier, microelectrode and a dendritic neuron model consisting of an isopotential cell and terminated finite equivalent cylinder representation of the dendrites are presented here. These studies show that the introduction of fast components of the response to intracellular current transients by the redistribution of applied charge in dendrite neurons may sometimes make it impossible to correctly apply the conventional methods of capacitance compensation and bridge balance. If the high-frequency response of the intracellular recording amplifier has sufficient fidelity, however, these adjustments can be made to a sufficient degree of accuracy using the response to sine wave calibration signals of varying frequency.