ABSTRACT
The firing patterns of either single neurons or clusters of neurons in living animals in response to physiological stimuli are obtained by extracellular recording. This technique uses two fine electrodes usually of tungsten or stainless steel. One, the exploring (focal) electrode is placed as close as possible to a neuron. The second, indifferent electrode is placed at a convenient distance. Neuron activity will cause currents to flow between the two electrodes. These currents are amplified and fed to a computer. By convention, if the exploring electrode is positive with respect to the indifferent electrode an upward deflection is recorded. The polarity, shape, amplitude, and timing of the recorded waveform generated by neural activity will depend on the position of the electrodes. The closer the exploring electrode is to the neuron, the larger the measured signal. Changing the distance between the two electrodes or altering their relative positions will modify all the above parameters. All of this can make extracellular recordings hard to interpret.
