Responses to rhythmical stimulation of the cerebral cortex.—Preliminary communication

Abstract

François-Franck and Pitres (1) in 1878-79 showed, by graphic analysis of movement produced by stimulation of the cortex cerebri, that complete fusion of responses did not occur until the frequency of the stimulation was increased above 45 per second. With the same apparatus they found that a muscle tetanus showed the stimulus rhythm up to the same frequency, and no further. Horsley and Schafer (2) in 1886, after a number of experiments on both voluntary contraction and movement by cortical stimulation, concluded that: “The rate of the rhythm is not the same as that of the excitation except when the frequency of excitation is 10 per second or less. With all higher rates of excitation the rhythm of muscular response is maintained at a fairly uniform rate of about 10 per second” (p. 105). Horsley and Schafer discuss the results of Françis-Franck and Pitres, quoting a statement from which they conclude that these authors modify their former conclusions; Luciani (3) also refers to this so-called modification. We find, however, on referring to François-Franck and Pitres’ paper (4), that their statement is to the effect that the regularity of cortical myograms is not as complete as in muscle nerve tetanus. They do not modify their original assertion that a stimulus rhythm of up to 45 per second to the cortex can appear in the muscle response. It seemed advisable to repeat these experiments, using an accurate torsion-wire myograph. The electromyogram has been recorded simultaneously; as far as we can ascertain this is the first attempt at the analysis of the action-currents due to cortical stimulation. The results obtained from the first three experiments are of some interest, therefore this preliminary communication is being made; further experiments are being carried out.