Brain Research, 85 (1975) 103-107 © Elsevier ScientificPublishing Company, Amsterdam - Printed in The Netherlands
103
Phase dependent reflex reversal during walking in chronic spinal cats
H. FORSSBERG, S. GRILLNER AND S. ROSSIGNOL Department of Physiology, University of GOteborg, GOteborg (Sweden)
(Accepted November 8th, 1974)
Cats spinalized (Th 12) a week or two after birth can, when they grow up, occasionally use their hindlimbs for walking 1~, although the hindquarter tends to fall to one side due to a reduced equilibrium control. However, when the cats are placed on a treadmill, this deficit can be compensated for by holding the tail. Then the cats can walk or gallop according to the speed of the treadmill belt with enough force to support their body weight and with patterns of joint angles and EMG similar to that of the intact cat 6. In the present experiments the ability of such chronic spinal cats to meet with obstacles impeding the foot during locomotion was investigated (21 experiments in 2 cats). When tactile stimulation is applied to the dorsum of the foot during the swing phase, the whole limb invariably enhances its flexion so as to overcome the obstacle, and then continues walking. Fig. 1A shows redrawings from a film (64 frames/sec) of the movement before, during and after contact to the dorsum of the foot. After contact, an enhanced flexion occurs in all joints bringing the limb well above and in front of the obstacle. E M G recording of a knee flexor semitendinosus (St) and contact trace synchronized to the film are shown below. Just after contact, a burst of activity occurs in St preceding the enhanced flexion movement. Similar responses occur in other flexors tested (tibialis anterior and iliopsoas). No effect is seen in the antagonist muscle quadriceps (Q). Even very modest stimuli applied with a straw or a small twig to the dorsum of the foot can elicit this movement during locomotion. To further ensure that this was not due to small displacements of joints or muscles but to cutaneous stimulation, the response (EMG and its integrated version) was compared before (Fig. I B) and after (Fig. 1C) subcutaneous local anaesthesia (Xylocaine 2 ~ ) of a 2 cm × 3 cm area on the dorsum o f the foot. Note the large synchronous response in St occurring after contact (Fig. 1B), particularly evident in the integrated record (see also Fig. 2A) where it is larger than the more prolonged 'locomotor burst'. After anaesthesia no response whatsoever could be obtained from the same region when applying the same stimulus. The limb would just push forward without overcoming the obstacle by flexion (see the prolonged contact trace in Fig. I C). Hence it was concluded that this response depended on cutaneous receptors.
104
c c
St
v
C
anesthesia St . . . . . . . . l*i,Jt
int.St . . . . . . . . . . .
~'~---
I 0 ÷ 5 0 ms c
Is
Fig. 1. Contact reaction during the swing phase of locomotion. A : redrawing of 5 selected frames of a 16 mm film (64 frames/sec) synchronized to an oscilloscope film by means of clocks synchronously photographed on both, representing a contact reaction during the swing phase of locomotion. The first frame shows the limb lifted up and advancing forwards. Upon contact (2nd frame) with the obstacle, represented by the black square, the limb starts to flex (3rd frame), passes over the obstacle (4th frame) and goes well in front of it (5th frame). In this case. the contact was made by a strain gauge mounted on a plexiglass rod. In the lower records, the first trace represents the output of the strata gauge (c) and the second one the activity in St recorded by means of implanted copper wires insulated except at the tip z. B: similar response recorded at low speed on a Mingograph ink recorder with a straight frequency response up to 1200 Hz. The first trace is the raw EMG of St and the second trace, its integrated versionL Upon contact (c) occurring after the St burst, a large response is observed. C: same as in B but after anaesthesia of the dorsum of the paw. No response occurs with the contact. The limb pushes on the strain gauge giving rise to a prolonged contact period. The limb succeeds in flexing later on after considerable stretching. In all examples, the treadmill speed was set at 0.25 m/sec.
In order to have more c o n s t a n t s t i m u l a t i o n conditions, two small silver plates were applied o n the skin o f the d o r s u m of the foot. W e a k s t i m u l a t i o n (t or 5 msec single pulses, a b o u t 2 m A ) w o u l d then result in responses identical to t h e ones observed after surface c o n t a c t (Fig. 2A). Their latency can be as short as 10 msec (stimulus to onset of E M G ) . T o test if the stimulus was equally effective in all phases of l o c o m o t i o n a circuit was designed to trigger the s t i m u l a t i o n by the onset of St activity a n d to apply it, with a delay unit, in different phases of the step cycle. Fig. 2 A shows the response o f St in 4 different phases. It can be seen that during, a n d for some period after, the flexor activity large responses are o b t a i n e d (first two examples) b u t in the s u b s e q u e n t part o f the step cycle c o r r e s p o n d i n g to the extension phase, the responses decrease sharply a n d disappear completely in the flexor (last two examples). O n the other h a n d , the same stimulus applied d u r i n g the extension phase results i n a large response in the extensor Q (Fig. 2C). C o r r e s p o n d i n g l y , a mechanical
105 contact as in Fig. 1 applied during the extension phase results in an extensor activation without effect in the flexor (Fig. 2B). This results in a markedly enhanced extension, which also becomes shorter. Sometimes, as in Fig. 2C, a very small activity can be seen in St but in other cases no response occurs (Fig. 2A, last example). Hence, an identical tactile stimulus applied to the dorsum of the foot gives rise either to a marked flexion or a marked extension response depending entirely on the phase of the step cycle in which the stimulus occurs. 'Reflex reversals' have been described before depending on limb positionS,Xtn 2 or when comparing a reflex effect during standing and walking 9. To our knowledge, however, this is the first time that a phase dependent 'reflex reversal' is described during an ongoing movement, i.e. a stimulus activates a given set of muscles in one phase, and in the other, their antagonists. This emphasizes the risk of extrapolating reflex effects studied in motionless preparations to the moving animals. Indeed, in the latter case, effects evoked by a given stimulus can apparently be channeled to one or another group of muscles depending on the phase of the movement. We cannot yet
A
B
St ~
st
int. St - . ~ .
Q
] st
~
int. St - - " " - .....
C
( '
~
J
IS
7-_
1
L : :
-
"
D
~ :~ •
Is
Fig. 2. Phase-dependent reflex reversal between quadriceps and semitendinosus. A: electrical stimulation of the foot dorsum with a 1 msec pulse, 2 mA delivered at 4 different phases of the step cycle. A stimulus applied in this way between the two plates on the shaved skin can be regarded as weak and is just perceptible when placed on the experimentor's tongue. Identification of traces is as in Fig. lB. In the first record, the stimulus falls at the end of the St burst and gives a large response, saturating the integrator. In the second set, the response is very large even if the stimulation occurs clearly after the St burst. In the third set, the response is smaller than before and in the last set, when the stimulation occurs well into the extension phase, the response is absent in St. B: contact reaction during extension phase. The activity of St alternates with that of Q. When the dorsum of the foot is touched (c), in this case with a small plate forming a microswitch, a large burst occurs in Q. This is best seen in the integrated version of Q showing a much larger activity than in the preceding and following cycles. Note that there is no response in St upon contact but there is a strong flexion which follows the response in Q. C: electrical stimulation during extension phase. A very large response occurs in Q. The treadmill speed is 0.25 m/sec for all records.
106 explain how the reversal is achieved but the following 3 neuronal mechanisms can be considered. Firstly, a central spinal generatorZ,V,S could phasicalty switch between reflex pathways while activating muscle groups sequentially throughout the step cycle. Secondly, pathways both to flexors and extensors could be continuously open but the stimulus would only be effective when the excitability level is high in one or the other group. Thirdly, interaction from other reflex pathways activated during stepping could, at an interneuronal level, switch between the different pathways, The second alternative appears unlikely since the phase during which the response can be obtained in antagonist muscles is not tightly linked to the phase of their activity (Fig. 2A). We tend to favour the first alternative although the third can by no means be excluded. The reflex appears functionally very meaningful in that a fixed obstacle impeding the movement of the limb can be overcome by an additional flexion during the swing phase. During the stance phase, on the other hand, the most effective way for the animal to get over a moving object touching its paw would be to perform an increased rapid extension followed by flexion. The effective region and the reflex during flexion are similar to the tactile placing response which indeed can be evoked in the chronic spinal preparation 4. Tactile placing is described in motionless animals 1 and the latency is in the order of 25-30 msec TM. The shorter latency o f the response studied here could be due to a more effective transmission in the active preparation than in the motionless cat. If the present reflex is identical to tactile placing, the role of the latter could be understood in functional terms which has hardly yet been the case: Furthermore, the observed reflex reversal depending on the phase of locomotion adds another important dimension to the meaningful processing of sensory information during movement. This study was supported by the Swedish Medical Research Council (No. 30-26). S. R. was supported by the Canadian Medical Research Council.
1 BARD, P., Studies on the cerebral cortex. I. Localized control of placing and hopping reactions in the cat and their normal management by small cortical remnants, Arch. Neurol. Psychiat. (Chic.),
30 (1933) 40-74. 2 BROWN,T. G., The intrinsic factors in the act of progression in the mammal, Proc. roy. Soc. B, 84 (1911) 308-319. 3 FORSSBERG,H., AND GRILLNER,S., The locomotion of the acute spinal cat injected with clonidine i.v., Brain Research, 50 (1973) 184-186. 4 FORSSBERG,H., GRILLNER,S., ANDSJ'~STROM,A., Tactile placing reactions in chronic spinal kittens, Acta physiol, scand., 92 (1974) 114-120, 5 GOTTLIEB, G. L., AND AGARWAL, G. C., Filtering of electromyographic signals, Amer. J. phys. Med., 49 (1970) 142-146. 6 GRILLNER, S., Locomotion in the spinal cat. In R. B. STEIN, K. G. PEARSON~ R. S. SM1THAND J. B. REDFORD(Eds.), Control of PostUre and Locomotion, Plenum Press, New York. 1973, pp.
515-535. 7 GR1LLNER,S., Locomotion in vertebrates - - central mechanisms and reflex interaction, Physiol. Rev., (1975) in press. 8 JANKOWSKA,E., JUKES,M. G. M., LUND, S., AND LUNDBERG,A., The effect of DOPA on the spinal
107
9 10 11 12 13
cord. 6. Half-centre organization of interneurones transmitting effects from the flexor reflex afferents, Acta physiol, scand., 70 (1967) 389402. LISIN, V. V., FRANKSTEIN, S. I., AND RECHTMANN, M. B., The influence of locomotion on flexor reflex of the hindlimb in cat and man, Exp. Neurol., 38 (1973) 180-183. LUNDBERG, A., The significance of segmental spinal mechanisms in motor control, Proceedings of Symposial Papeta" 4th International Biophysics Congress, Moscow, 1972. MAGNUS, R., Zur Regelung der Bewegungen durch das Zentralnervensystem. Mitteilung I. Pfliigers Arch. ges. Physiol., 130 (1909) 219-252. MAGNUS, R., Kih'perstellung, Springer, Berlin, 1924, pp. 24-49. SHURRAGER,P. S., AND DYKMAN, R. A., Walking spinal carnivores, J. eomp. physiol. Psychol., 44 (1951) 252 262.
103
Phase dependent reflex reversal during walking in chronic spinal cats
H. FORSSBERG, S. GRILLNER AND S. ROSSIGNOL Department of Physiology, University of GOteborg, GOteborg (Sweden)
(Accepted November 8th, 1974)
Cats spinalized (Th 12) a week or two after birth can, when they grow up, occasionally use their hindlimbs for walking 1~, although the hindquarter tends to fall to one side due to a reduced equilibrium control. However, when the cats are placed on a treadmill, this deficit can be compensated for by holding the tail. Then the cats can walk or gallop according to the speed of the treadmill belt with enough force to support their body weight and with patterns of joint angles and EMG similar to that of the intact cat 6. In the present experiments the ability of such chronic spinal cats to meet with obstacles impeding the foot during locomotion was investigated (21 experiments in 2 cats). When tactile stimulation is applied to the dorsum of the foot during the swing phase, the whole limb invariably enhances its flexion so as to overcome the obstacle, and then continues walking. Fig. 1A shows redrawings from a film (64 frames/sec) of the movement before, during and after contact to the dorsum of the foot. After contact, an enhanced flexion occurs in all joints bringing the limb well above and in front of the obstacle. E M G recording of a knee flexor semitendinosus (St) and contact trace synchronized to the film are shown below. Just after contact, a burst of activity occurs in St preceding the enhanced flexion movement. Similar responses occur in other flexors tested (tibialis anterior and iliopsoas). No effect is seen in the antagonist muscle quadriceps (Q). Even very modest stimuli applied with a straw or a small twig to the dorsum of the foot can elicit this movement during locomotion. To further ensure that this was not due to small displacements of joints or muscles but to cutaneous stimulation, the response (EMG and its integrated version) was compared before (Fig. I B) and after (Fig. 1C) subcutaneous local anaesthesia (Xylocaine 2 ~ ) of a 2 cm × 3 cm area on the dorsum o f the foot. Note the large synchronous response in St occurring after contact (Fig. 1B), particularly evident in the integrated record (see also Fig. 2A) where it is larger than the more prolonged 'locomotor burst'. After anaesthesia no response whatsoever could be obtained from the same region when applying the same stimulus. The limb would just push forward without overcoming the obstacle by flexion (see the prolonged contact trace in Fig. I C). Hence it was concluded that this response depended on cutaneous receptors.
104
c c
St
v
C
anesthesia St . . . . . . . . l*i,Jt
int.St . . . . . . . . . . .
~'~---
I 0 ÷ 5 0 ms c
Is
Fig. 1. Contact reaction during the swing phase of locomotion. A : redrawing of 5 selected frames of a 16 mm film (64 frames/sec) synchronized to an oscilloscope film by means of clocks synchronously photographed on both, representing a contact reaction during the swing phase of locomotion. The first frame shows the limb lifted up and advancing forwards. Upon contact (2nd frame) with the obstacle, represented by the black square, the limb starts to flex (3rd frame), passes over the obstacle (4th frame) and goes well in front of it (5th frame). In this case. the contact was made by a strain gauge mounted on a plexiglass rod. In the lower records, the first trace represents the output of the strata gauge (c) and the second one the activity in St recorded by means of implanted copper wires insulated except at the tip z. B: similar response recorded at low speed on a Mingograph ink recorder with a straight frequency response up to 1200 Hz. The first trace is the raw EMG of St and the second trace, its integrated versionL Upon contact (c) occurring after the St burst, a large response is observed. C: same as in B but after anaesthesia of the dorsum of the paw. No response occurs with the contact. The limb pushes on the strain gauge giving rise to a prolonged contact period. The limb succeeds in flexing later on after considerable stretching. In all examples, the treadmill speed was set at 0.25 m/sec.
In order to have more c o n s t a n t s t i m u l a t i o n conditions, two small silver plates were applied o n the skin o f the d o r s u m of the foot. W e a k s t i m u l a t i o n (t or 5 msec single pulses, a b o u t 2 m A ) w o u l d then result in responses identical to t h e ones observed after surface c o n t a c t (Fig. 2A). Their latency can be as short as 10 msec (stimulus to onset of E M G ) . T o test if the stimulus was equally effective in all phases of l o c o m o t i o n a circuit was designed to trigger the s t i m u l a t i o n by the onset of St activity a n d to apply it, with a delay unit, in different phases of the step cycle. Fig. 2 A shows the response o f St in 4 different phases. It can be seen that during, a n d for some period after, the flexor activity large responses are o b t a i n e d (first two examples) b u t in the s u b s e q u e n t part o f the step cycle c o r r e s p o n d i n g to the extension phase, the responses decrease sharply a n d disappear completely in the flexor (last two examples). O n the other h a n d , the same stimulus applied d u r i n g the extension phase results i n a large response in the extensor Q (Fig. 2C). C o r r e s p o n d i n g l y , a mechanical
105 contact as in Fig. 1 applied during the extension phase results in an extensor activation without effect in the flexor (Fig. 2B). This results in a markedly enhanced extension, which also becomes shorter. Sometimes, as in Fig. 2C, a very small activity can be seen in St but in other cases no response occurs (Fig. 2A, last example). Hence, an identical tactile stimulus applied to the dorsum of the foot gives rise either to a marked flexion or a marked extension response depending entirely on the phase of the step cycle in which the stimulus occurs. 'Reflex reversals' have been described before depending on limb positionS,Xtn 2 or when comparing a reflex effect during standing and walking 9. To our knowledge, however, this is the first time that a phase dependent 'reflex reversal' is described during an ongoing movement, i.e. a stimulus activates a given set of muscles in one phase, and in the other, their antagonists. This emphasizes the risk of extrapolating reflex effects studied in motionless preparations to the moving animals. Indeed, in the latter case, effects evoked by a given stimulus can apparently be channeled to one or another group of muscles depending on the phase of the movement. We cannot yet
A
B
St ~
st
int. St - . ~ .
Q
] st
~
int. St - - " " - .....
C
( '
~
J
IS
7-_
1
L : :
-
"
D
~ :~ •
Is
Fig. 2. Phase-dependent reflex reversal between quadriceps and semitendinosus. A: electrical stimulation of the foot dorsum with a 1 msec pulse, 2 mA delivered at 4 different phases of the step cycle. A stimulus applied in this way between the two plates on the shaved skin can be regarded as weak and is just perceptible when placed on the experimentor's tongue. Identification of traces is as in Fig. lB. In the first record, the stimulus falls at the end of the St burst and gives a large response, saturating the integrator. In the second set, the response is very large even if the stimulation occurs clearly after the St burst. In the third set, the response is smaller than before and in the last set, when the stimulation occurs well into the extension phase, the response is absent in St. B: contact reaction during extension phase. The activity of St alternates with that of Q. When the dorsum of the foot is touched (c), in this case with a small plate forming a microswitch, a large burst occurs in Q. This is best seen in the integrated version of Q showing a much larger activity than in the preceding and following cycles. Note that there is no response in St upon contact but there is a strong flexion which follows the response in Q. C: electrical stimulation during extension phase. A very large response occurs in Q. The treadmill speed is 0.25 m/sec for all records.
106 explain how the reversal is achieved but the following 3 neuronal mechanisms can be considered. Firstly, a central spinal generatorZ,V,S could phasicalty switch between reflex pathways while activating muscle groups sequentially throughout the step cycle. Secondly, pathways both to flexors and extensors could be continuously open but the stimulus would only be effective when the excitability level is high in one or the other group. Thirdly, interaction from other reflex pathways activated during stepping could, at an interneuronal level, switch between the different pathways, The second alternative appears unlikely since the phase during which the response can be obtained in antagonist muscles is not tightly linked to the phase of their activity (Fig. 2A). We tend to favour the first alternative although the third can by no means be excluded. The reflex appears functionally very meaningful in that a fixed obstacle impeding the movement of the limb can be overcome by an additional flexion during the swing phase. During the stance phase, on the other hand, the most effective way for the animal to get over a moving object touching its paw would be to perform an increased rapid extension followed by flexion. The effective region and the reflex during flexion are similar to the tactile placing response which indeed can be evoked in the chronic spinal preparation 4. Tactile placing is described in motionless animals 1 and the latency is in the order of 25-30 msec TM. The shorter latency o f the response studied here could be due to a more effective transmission in the active preparation than in the motionless cat. If the present reflex is identical to tactile placing, the role of the latter could be understood in functional terms which has hardly yet been the case: Furthermore, the observed reflex reversal depending on the phase of locomotion adds another important dimension to the meaningful processing of sensory information during movement. This study was supported by the Swedish Medical Research Council (No. 30-26). S. R. was supported by the Canadian Medical Research Council.
1 BARD, P., Studies on the cerebral cortex. I. Localized control of placing and hopping reactions in the cat and their normal management by small cortical remnants, Arch. Neurol. Psychiat. (Chic.),
30 (1933) 40-74. 2 BROWN,T. G., The intrinsic factors in the act of progression in the mammal, Proc. roy. Soc. B, 84 (1911) 308-319. 3 FORSSBERG,H., AND GRILLNER,S., The locomotion of the acute spinal cat injected with clonidine i.v., Brain Research, 50 (1973) 184-186. 4 FORSSBERG,H., GRILLNER,S., ANDSJ'~STROM,A., Tactile placing reactions in chronic spinal kittens, Acta physiol, scand., 92 (1974) 114-120, 5 GOTTLIEB, G. L., AND AGARWAL, G. C., Filtering of electromyographic signals, Amer. J. phys. Med., 49 (1970) 142-146. 6 GRILLNER, S., Locomotion in the spinal cat. In R. B. STEIN, K. G. PEARSON~ R. S. SM1THAND J. B. REDFORD(Eds.), Control of PostUre and Locomotion, Plenum Press, New York. 1973, pp.
515-535. 7 GR1LLNER,S., Locomotion in vertebrates - - central mechanisms and reflex interaction, Physiol. Rev., (1975) in press. 8 JANKOWSKA,E., JUKES,M. G. M., LUND, S., AND LUNDBERG,A., The effect of DOPA on the spinal
107
9 10 11 12 13
cord. 6. Half-centre organization of interneurones transmitting effects from the flexor reflex afferents, Acta physiol, scand., 70 (1967) 389402. LISIN, V. V., FRANKSTEIN, S. I., AND RECHTMANN, M. B., The influence of locomotion on flexor reflex of the hindlimb in cat and man, Exp. Neurol., 38 (1973) 180-183. LUNDBERG, A., The significance of segmental spinal mechanisms in motor control, Proceedings of Symposial Papeta" 4th International Biophysics Congress, Moscow, 1972. MAGNUS, R., Zur Regelung der Bewegungen durch das Zentralnervensystem. Mitteilung I. Pfliigers Arch. ges. Physiol., 130 (1909) 219-252. MAGNUS, R., Kih'perstellung, Springer, Berlin, 1924, pp. 24-49. SHURRAGER,P. S., AND DYKMAN, R. A., Walking spinal carnivores, J. eomp. physiol. Psychol., 44 (1951) 252 262.
