Unipolar and bipolar electrodes in self-stimulation experiments

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Abstract
Experiments were conducted in which response rates for different intensities of reinforcing intracranial stimulation were obtained with both bipolar and unipolar electrodes. Subsequent experiments were designed to clarify differences resulting from these two types of stimulation. Experimental subjects were albino rats and rhesus monkeys. Using biphasic stimulation it was found that self-stimulation rates were consistently lower with unipolar electrodes than with bipolar ones. These lowered response rates appeared to result from the alternation of the cathode and anode between the deep electrode and the indifferent surface electrode. Subsequent experiments with monophasic current demonstrated the significance of the location of the cathode and anode for self-stimulation experiments. The results of an attempt to evaluate the relative area of effective current spread with unipolar and bipolar electrodes are also reported. It was found that in anesthetized monkeys with unipolar electrodes, rhythmic vocalization could be elicited more often, and over a significantly greater area surrounding the periaqueductal gray than when bipolar electrodes were used.

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