STUDIES IN THE PHYSIOLOGY OF THE NERVOUS SYSTEM. XVIII.: THE SUCCESSIVE EFFECTS OF THE COMPOUNDING OF REFLEXES WHERE THE “PURE” REACTIONS ARE ABNORMAL (IPSILATERAL EXTENSION OR CONTRALATERAL FLEXION) IN DECEREBRATE PREPARATIONS
Authors: Brown T. Graham 
Published: December 2014

1. In the present paper the successive effects of the compounding of reflexes are examined in instances in which the abnormal responses of ipsilateral extension or of contralateral flexion occurred.

2. Where the ipsilateral response is one of abnormal extension it has been compounded with the normal contralateral extension‐reflex.

3. When the two stimuli are synchronously terminated it has been found that the extensor after‐discharge may be better marked than in the “pure” reactions. It may carry on the summated level of extensor contraction which obtains during the period of double stimulation.

4. If the abnormal ipsilateral extension is used as the “background” reaction and is interrupted by the normal contralateral extension, there may appear an augmentation of extension in the third phase of the compound reaction—that after withdrawal of the interrupting stimulus. On withdrawal of the ipsilateral stimulus there may be a further slight augmentation which resembles an “extensor rebound contraction after excitation” even where that is not present in the “pure” reaction. Where there is no extensor after‐discharge in the “pure” ipsilateral extension‐reflex, but one in the “pure” contralateral extension‐reflex, there may yet appear an extensor after‐discharge in the fourth phase of a reaction in which the two are compounded with the ipsilateral as “background.” As augmentation of extensor contraction may then occur in the preceding third phase (that after withdrawal of the contralateral stimulus and before the final withdrawal of the ipsilateral “background” stimulus), it looks as if the extensor after‐discharge of the normal contralateral reaction may add itself to the abnormal immediate extensor contraction of the ipsilateral reaction and persist after the withdrawal of the latter reaction. In other cases, however, even where there is well‐marked extensor after‐discharge in the contralateral reaction, relaxation appears in the third phase of the compound reaction, and a still further relaxation in the fourth phase. This appears to occur in cases in which with increase of strength of the ipsilateral stimulus there is decrease in the value of the abnormal extension‐reflex.

5. If the normal contralateral extension‐reflex is used as “background” and interrupted by the abnormal ipsilateral extension‐reflex, there sometimes is seen slight extensor relaxation and sometimes augmentation of extensor contraction during the period of double stimulation. If there is an “extensor rebound contraction after excitation” in the abnormal ipsilateral extension‐reflex, and sometimes if there is not, augmentation of extensor contraction to a level greater than that in the “pure” contralateral reaction may occur in the third phase of the compound reaction. In the fourth phase—on withdrawal of the “background” contralateral extension‐reflex—an extensor after‐discharge may be carried on at this augmented level. In one instance in which the interrupting ipsilateral extension‐reflex was liminal there occurred extensor relaxation in the fourth phase although there was an extensor after‐discharge in the “pure” contralateral extension‐reflex used as “background.”

6. When the compounding of reflexes is examined in those experiments in which the “pure” ipsilateral reaction in response to weak stimuli is one of abnormal extension, but that in response to strong stimuli is one of normal flexion, the successive effects of the compounding have been examined in cases in which the two stimuli are synchronously terminated. In such cases during double stimulation there may be extensor augmentation of contraction when the ipsilateral stimulus is weak; relative depression of the degree of extensor contraction when it is of intermediate strength; and actual extensor relaxation when the ipsilateral stimulus is strong. In these circumstances there may be an extensor after‐discharge on synchronous withdrawal of the two stimuli. This appears to be proportional in its extent of extensor contraction to the degree of extensor contraction during the preceding phase of double stimulation; but with the stronger ipsilateral stimuli the extensor terminal phenomenon may be of greater extent of contraction than that exhibited by the extensor during double stimulation, so that it has the form of an “extensor rebound contraction after excitation”; while there may appear an “extensor rebound contraction after inhibition” where the ipsilateral stimulus is strong and there is actual extensor relaxation during double stimulation.

7. When, under the same conditions, the two stimuli are not synchronously terminated, but the contralateral stimulus is used as a “background” which is interrupted by a briefer ipsilateral stimulus, the same phenomena may be observed in the phase of double stimulation. In the third phase of the compound reaction, when the contralateral stimulus is continued after the withdrawal of the interrupting ipsilateral stimulus, there may occur augmented extensor contraction. The level of this contraction may be greater than that of the sum of the extensor contractions in the “pure” contralateral reflex, and in the extensor rebound of the ipsilateral reflex. It is sometimes of greater height the stronger the previous ipsilateral stimulus and the smaller the extent of extensor contraction during double stimulation. The curve of extensor contraction in the third phase may shew two waves—one corresponding to that of restitution of extensor contraction conditioned by the contralateral stimulus, and the other corresponding to that of the extensor rebound contraction of the ipsilateral reaction. In the fourth phase extensor after‐discharge proportional in extent to the preceding extensor contraction of the third phase may occur. Sometimes extensor relaxation may be observed in the fourth phase, and is then a sharper movement the stronger the interrupting ipsilateral stimulus.

8. If, of the two stimuli, the ipsilateral is used as “background” under the same conditions and interrupted by the normal contralateral extension‐reflex, there may be extensor augmentation during the phase of double stimulation, but this is smaller the stronger the “background” ipsilateral stimulus. In the third phases extensor relaxation has been observed, and this is greater the stronger the ipsilateral “background” is. If there be a maintained extensor terminal contraction in the “pure” ipsilateral reflex, this may appear as a more transient phenomenon in the fourth phase of the compound phenomenon—that on withdrawal of the ipsilateral “background.”

9. Where the contralateral response is one of abnormal flexion it has been compounded with the normal ipsilateral flexion‐reflex.

10. When the two stimuli are synchronously terminated extensor rebound contraction may occur although not present in either “pure” reaction at the strengths of stimuli used. Where flexor rebound contraction occurs in the “pure” reactions that may occur on synchronous termination of two subliminal stimuli which do not evoke any reaction during double stimulation; and a larger flexor rebound may occur when the subliminal stimuli are sufficiently strong to evoke a flexion‐reflex during double stimulation. Where supraliminal strengths of stimulation are used the flexor rebound contraction on synchronous withdrawal of the two stimuli is greater in extent than that of either “pure” reaction.

11. Where the two stimuli are not synchronously terminated, but the “background” of abnormal contralateral flexion is left in action after the withdrawal of the interrupting ipsilateral stimulus, augmentation of flexion commonly occurs during the period of double stimiulation. From the level of this augmentation there is commonly a degree of flexor relaxation in the third phase of the compound reaction, but the flexor nevertheless remains at a level of contraction much higher than that which obtains at the same point in the “pure” contralateral flexion‐reflex. This may occur even in cases where after the “pure” ipsilateral flexion‐reflex there is no flexor rebound but only flexor relaxation. Where there is flexor rebound in the “pure” ipsilateral flexion‐reflex there occurs additional flexor augmentation in the third phase of the compound reaction. In the fourth phase of the compound reaction there may occur extensor rebound contraction when that is present in the “pure” contralateral reflex. It may be greater in extent than the “pure” rebound, and may occur at periods in an experiment when that rebound is not present with the strength of contralateral stimulation used. Where flexor rebound occurs in the “pure” contralateral flexion‐reflex the same phenomenon but of larger extent is observed on withdrawal of the contralateral “background” in the compound reaction. It may be followed by a maintained extensor rebound contraction not present in the “pure” contralateral reaction.

12. Where the “background” is one of normal ipsilateral flexion and is interrupted by abnormal contralateral flexion, augmentation of flexor contraction occurs in the third phase of the compound reaction. This may be the case where there is no flexor rebound contraction in the “pure” contralateral reflex. It may even be present where the “pure” contralateral reaction is di—phasic, and where the late extensor contraction during stimulation is followed by a well‐marked extensor after‐discharge. (This seems to suggest that in the terminal phenomena of the contralateral reflex, even where there is uncomplicated extensor after‐discharge, there is a primary flexion factor which is there submerged but in other cases may be evident in a primary flexor rebound contraction.) Where there is a flexor rebound contraction in the “pure” contralateral reflex the flexor augmentation of contraction in the third phase of the compound reaction may be greater in extent than that of the flexor rebound contraction in the “pure” contralateral reflex. The flexor augmentation of contraction in the third phase is usually greater the stronger the interrupting contralateral stimulus is. Where the two compounded stimuli are subliminal and of sufficient weakness there may appear no flexor contraction in the phase of double stimulation, but that may appear for the first time in the third phase of the compound reaction on withdrawal of the contralateral stimulus. In the fourth phase of the compound reaction—that on withdrawal of the “background” ipsilateral stimulus—flexor rebound contraction may appear. This may appear when absent in the “pure” ipsilateral flexion‐reflex—as when the ipsilateral stimulus is subliminal. When present in the “pure” ipsilateral flexion‐reflex it is exaggerated in the fourth phase of a compound reaction. But extensor rebound contraction may appear in this phase even when absent in the “pure” ipsilateral reflex. This has been observed in instances in which the “pure” contralateral reflex is di‐phasic and the secondary extensor contraction which occurs during stimulation is continued as a well‐marked extensor after‐discharge. It is possible that this may last through the third phase (where primary flexor augmentation of contraction occurs) and again become evident in the fourth. Where extensor rebound contraction is present in the “pure” ipsilateral flexion‐reflex as well as in the “pure” abnormal contralateral flexion‐reflex, it may appear in the fourth phase of the compound reaction upon withdrawal of the “background” ipsilateral stimulus. It may then be of greater extent than that of the “pure” ipsilateral reflex.

13. These experiments give additional evidence that, just as in the immediate phenomena of reflex combination there is a compounding of the two reactions, so too in the successive phenomena there is a compounding of two activities. Of these the one is the immediate activity of the “background” reaction left in action and the other is that of the terminal reflex phenomena of the interrupting reflex. The two seem to combine to condition the phenomena of the third phase of such compound reactions. But there seems to be some evidence also that the terminal phenomena of the interrupting reflex can persist through the remainder of the period of the “background” reflex (third phase) and then compound with the terminal phenomena of that “background” reaction.

14. And these results also appear to give additional support to the surmise that, just as it seems probable that the immediate phenomena of the “pure” reflex are conditioned by the compounding of two opposite activities (flexion and extension) of which the one is preponderant, so too it seems probable that there is a similar compounding of the two activities in the “pure” terminal reflex phenomena.