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Abstract: The present study was undertaken with one dog, on whose cortex, at the region of the sigmoid gyrus, were imbedded two permanent electrodes known respectively as electrode A and electrode B. Under stimulation, electrode A gives movement of the left hind leg, and electrode B elicits movement of the toes of the left front leg.The main aim of the experiment is to determine the minimal strength in voltage for eliciting the first appreciable motor response, when the frequency of the stimulating current is under control. With an ordinary audio-oscillator to administer the stimulus frequencies, the range of frequencies utilized is 20—20,000 cycles.For the same frequencies, the minimal voltage for eliciting the motor response varies considerably from one sitting to another (see Table 1), but within the same sitting the same frequencies, even when repeated with many other frequencie intervening, require closely similar minimal voltages. Furthermore, a clear trend is always present in the relationship between the frequency of the stimulating. current and the minimal voltage necessary for eliciting the motor response, i. e., within the range of frequencies used (20—20,000), the middle frequencies need farsmaller stimulus strength in voltage than either the lower or the higher ones to elicit the same motor response.It was found that the minimal effective voltage is lowest for the 300—1,000. cycles region. Frequencies lower than 300 or higher than 1,000 need higher voltage. Furthermore, frequencies from 300 downwards and from 1,000 upwards are accompanied by progressively higher voltage. Electrodes A and B yield closely similar results (see Table 3 and Fig. 2). Thus, the frequencies from 300 to 1,000 cycles may be considered as possessing the most effective stimulus value.Besides the definite frequency-voltage relationship just mentioned, frequency affects the type of motor response as that frequencies of 100 and below 100 no longer elicit the regular response of the leg or the toes alone, but give rise to neck. movement in addition. Neck movement becomes eventually the only motor response to frequencies 50—20. With electrode A the above mentioned phenomenon. appeared with great regularity (see Table 4).When the experiment was over, the dog was killed and its brain examined histologically. It is seen that both electrodes are in the sigmoid gyrus of the right hemisphere, but they enter into different depths. Electrode A penetrates into between layer Ⅴ and layer Ⅵ, while electrode B penetrates only into layer (see Figs. 4 and 5).

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