STUDIES IN THE PHYSIOLOGY OF THE NERVOUS SYSTEM. XIV.: IMMEDIATE AND SUCCESSIVE EFFECTS OF COMPOUND STIMULATION IN SPINAL PREPARATIONS

Abstract

1. In the present paper the immediate and successive effects of the compounding of stimuli have been examined in spinal preparations (low spinal and decapitate) as well in the de‐afferented condition as in the normal.2. During double stimulation (immediate effects) there is usually an algebraic summation of the “pure” reactions. This is such—as Sherrington has already pointed out—that the stronger the ipsilateral stimulus relatively is, the greater is the effect of extensor relaxation and flexor contraction during double stimulation; and the stronger the contralateral stimulus is, the greater is the effect of flexor relaxation and extensor contraction.3. When the time relations of the antagonised stimuli are changed, it is found upon the whole that the extension effect during double stimulation is greater the later a contralateral stimulus falls in the period of ipsilateral stimulation; and that the greater is the flexion effect the later an ipsilateral stimulus falls in the period of contralateral stimulation. But often the flexion effect is much greater when the two stimuli are commenced synchronously than when the ipsilateral is commenced a short time after the contralateral.4. Very rarely a slight augmentation of flexor contraction is seen at the commencement of the period of double stimulation when a contralateral stimulus is compounded against a background of weak flexion.5. Less rarely an actual augmentation of extensor contraction occurs during double stimulation, so that this is greater than in the “pure” extension‐reflex.6. This effect is, within limits, proportional to the relative preponderance of the strength of the contralateral stimulus. But if this be changed by weakening the strength of the ipsilateral stimulus, it is found that there exists an optimum relation of the strengths of the two stimuli, and that a further decrease of the strength of the ipsilateral stimulus is accompanied by a reduction of the augmented extensor contraction.7. It is also found that, within limits, this extensor augmentation of contraction during double stimulation is greater the later the contralateral stimulus falls in the period of the ipsilateral. But here too an optimum interval of time between the commencement of the ipsilateral stimulus and that of the interrupting contralateral exists. If the contralateral stimulus be applied at a greater interval of time, the extensor augmentation is decreased.8. Even where the “pure” contralateral reaction evokes abnormal flexion there may be flexor depression during double stimulation. This is seen where the strength of the ipsilateral stimulus is comparatively great. Where the two antagonistic stimuli are small, or subliminal, there may be flexor augmentation of contraction.9. The successive effects of the compounding of stimuli, as seen after withdrawal of one of the stimuli in the phase of double stimulation, seem chiefly to consist in flexion depression and extension augmentation.10. This is seen in the tendency for only a partial restitution of flexor contraction to occur when the ipsilateral stimulus is prolonged after the period of double stimulation. Sometimes no restitution of flexor contraction may occur. When it does occur, it seems to be greater the relatively greater is the strength of the ipsilateral stimulus.11. It is also seen in the tendency for extensor augmentation to occur when the contralateral stimulus is prolonged after the period of double stimulation. This is less the relatively stronger the ipsilateral stimulus is.12. These points mentioned in this summary are some of the chief ones described in this paper, but it is impossible to summarise briefly all the various observations contained in it.