scholarly journals Selective bilateral activation of leg muscles after cutaneous nerve stimulation during backward walking

2012 ◽  
Vol 108 (7) ◽  
pp. 1933-1941 ◽  
Author(s):  
Wouter Hoogkamer ◽  
Firas Massaad ◽  
Karen Jansen ◽  
Sjoerd M. Bruijn ◽  
Jacques Duysens
Keyword(s):  
Nerve Stimulation ◽  
Sural Nerve ◽  
Center Of Mass ◽  
Biceps Femoris ◽  
Medial Gastrocnemius ◽  
Reflex Activity ◽  
Emg Activity ◽  
Cutaneous Reflexes ◽  
Backward Walking ◽  
Cutaneous Reflex

During human locomotion, cutaneous reflexes have been suggested to function to preserve balance. Specifically, cutaneous reflexes in the contralateral leg's muscles (with respect to the stimulus) were suggested to play an important role in maintaining stability during locomotor tasks where stability is threatened. We used backward walking (BW) as a paradigm to induce unstable gait and analyzed the cutaneous reflex activity in both ipsilateral and contralateral lower limb muscles after stimulation of the sural nerve at different phases of the gait cycle. In BW, the tibialis anterior (TA) reflex activity in the contralateral leg was markedly higher than TA background EMG activity during its stance phase. In addition, in BW a substantial reflex suppression was observed in the ipsilateral biceps femoris during the stance-swing transition in some participants, while for medial gastrocnemius the reflex activity was equal to background activity in both legs. To test whether the pronounced crossed responses in TA could be related to instability, the responses were correlated with measures of stability (short-term maximum Lyapunov exponents and step width). These measures were higher for BW compared with forward walking, indicating that BW is less stable. However, there was no significant correlation between these measures and the amplitude of the crossed TA responses in BW. It is therefore proposed that these crossed responses are related to an attempt to briefly slow down (TA decelerates the center of mass in the single-stance period) in the light of unexpected perturbations, such as provided by the sural nerve stimulation.

scholarly journals Cutaneous inputs from perineal region facilitates and modulates spinal locomotor activity and reduces cutaneous reflexes from the foot in spinal cats

2020 ◽  
Author(s):  
Angèle N Merlet ◽  
Jonathan Harnie ◽  
Madalina Macovei ◽  
Adam Doelman ◽  
Nathaly Gaudreault ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Nerve Stimulation ◽  
Rhythmic Activity ◽  
Short Latency ◽  
Cutaneous Reflexes ◽  
Excitatory Effect ◽  
Reflex Responses ◽  
Cutaneous Reflex ◽  
Weight Support ◽  
Perineal Region

AbstractIt is well known that mechanically stimulating the perineal region potently facilitates hindlimb locomotion and weight support in mammals with a spinal transection (spinal mammals). However, how perineal stimulation mediates this excitatory effect is poorly understood. We evaluated the effect of mechanically stimulating (vibration or pinch) the perineal region on ipsilateral (9-14 ms onset) and contralateral (14-18 ms onset) short-latency cutaneous reflex responses evoked by electrically stimulating the superficial peroneal or distal tibial nerve in seven adult spinal cats where hindlimb movement was restrained. Cutaneous reflexes were evoked before, during, and after mechanical stimulation of the perineal region. We found that vibration or pinch of the perineal region effectively triggered rhythmic activity, unilateral and bilateral to nerve stimulation. When electrically stimulating nerves, adding perineal stimulation modulated rhythmic activity by decreasing cycle and burst durations and by increasing the amplitude of flexors and extensors. Perineal stimulation also disrupted the timing of the ipsilateral rhythm, which had been entrained by nerve stimulation. Mechanically stimulating the perineal region decreased ipsilateral and contralateral short-latency reflex responses evoked by cutaneous inputs, a phenomenon we observed in muscles crossing different joints and located in different limbs. The results suggest that the excitatory effect of perineal stimulation on locomotion and weight support is not mediated by increasing cutaneous reflex gain and instead points to an excitation of central pattern-generating circuitry. Our results are consistent with a state-dependent modulation of reflexes by spinal interneuronal circuits.Significance StatementMechanically stimulating the skin of the perineal region strongly facilitates hindlimb locomotion in mammals following a complete spinal cord injury (SCI). Despite its remarkable effectiveness in promoting hindlimb locomotion in spinal cord-injured mammals, we do not know how this is mediated. The present study provides data on how inputs from the perineal region interact with neuronal circuits that generate locomotor-like activity and reflexes from the foot. A better understanding of how inputs from the perineal region interact with neuronal circuits of the spinal cord could lead to non-invasive approaches to restore walking in people with SCI.

scholarly journals Mechanically stimulating the lumbar region inhibits locomotor-like activity and increases the gain of cutaneous reflexes from the paws in spinal cats

2020 ◽  
Vol 123 (3) ◽  
pp. 1026-1041
Author(s):  
Angèle N. Merlet ◽  
Jonathan Harnie ◽  
Madalina Macovei ◽  
Adam Doelman ◽  
Nathaly Gaudreault ◽  
...  
Keyword(s):  
Nerve Stimulation ◽  
Inhibitory Effect ◽  
Short Latency ◽  
Lumbar Region ◽  
Cutaneous Reflexes ◽  
Cutaneous Reflex ◽  
Thoracic Spinal ◽  
Weight Support ◽  
Reflex Gain ◽  
Excitatory Responses

Mechanically stimulating the dorsal lumbar region inhibits locomotion and reduces weight support during standing in rabbits and cats. However, how this inhibitory effect from the lumbar skin is mediated is poorly understood. Here we evaluated the effect of mechanically stimulating (vibration or pinch) the dorsal lumbar region on short-latency (8- to 13-ms onset) cutaneous reflex responses, evoked by electrically stimulating the superficial peroneal or distal tibial nerves, in seven adult cats with a low thoracic spinal transection (spinal cats). Cutaneous reflexes were evoked before, during, and after mechanical stimulation of the dorsal lumbar region. We found that mechanically stimulating the lumbar region by vibration or manual pinch abolished alternating bursts of activity between flexors and extensors initiated by nerve stimulation. The activity of extensor muscles was abolished bilaterally, whereas the activity of some ipsilateral flexor muscles was sustained during vibration/pinch. Mechanically stimulating the lumbar region increased ipsilateral and contralateral short-latency excitatory responses evoked by cutaneous inputs, a phenomenon that was generalized to muscles crossing different joints and located in different limbs. Our results indicate that the inhibitory effect on locomotion and weight support is not mediated by reducing cutaneous reflex gain and instead points to an inhibition of central pattern-generating circuitry, particularly the extensor component. The results provide greater insight into interactions between different types of somatosensory inputs within spinal motor circuits. NEW & NOTEWORTHY Vibration or pinch of the lumbar region in spinal-transected cats abolished alternating bursts of activity between flexors and extensors initiated by nerve stimulation. Mechanically stimulating the lumbar region increased ipsilateral and contralateral short-latency excitatory responses evoked by cutaneous inputs in hindlimb muscles. Sensory inputs from mechanoreceptors of the lumbar region do not mediate their inhibitory effect on locomotion and weight support by reducing the gain of short-latency excitatory cutaneous reflexes from the foot.

Ipsilateral and contralateral effects on cutaneous reflexes in a back muscle of the female rat: modulation by steroids relevant for reproductive behavior

1990 ◽  
Vol 64 (3) ◽  
pp. 835-846 ◽  
Author(s):  
S. Schwartz-Giblin ◽  
D. W. Pfaff
Keyword(s):  
Nerve Stimulation ◽  
The Body ◽  
Female Rats ◽  
Female Rat ◽  
Cutaneous Reflexes ◽  
Intravenous Injections ◽  
Cutaneous Reflex ◽  
Early Peak ◽  
Number Of Discharges ◽  
Back Extensor

1. Multiunit EMG recordings of cutaneous reflexes--evoked in the back extensor, lateral longissimus (LL), by bilateral stimulation of nerves to dorsal flank skin--were studied in ovariectomized female rats with and without estrogen pretreatment. 2. Poststimulus time (PST) histograms of data from rats with and without estrogen pretreatment show that the axial EMG response (10-30 ms) to ipsilateral (ipsi) flank skin nerve stimulation is significantly shorter in latency (1.4 ms) and 67% larger than the response to contralateral (contra) flank skin nerve stimulation recorded at the same site (n = 29 pairs). 3. When late EMG responses were also evoked at 50-120 ms in 37% of ipsi and 29% of contra cutaneous reflexes, the incidence of multiunit activity in the late peak was significantly greater in rats pretreated with silastics containing 100% estradiol (E) compared with 10% E or cholesterol controls. 4. When an ipsi cutaneous reflex in LL was conditioned by a stimulus to the contra flank skin nerve at a condition-test interval of 30 ms (C-T 30 ms), the average number of discharges in the early peak of the histogram was double that in the histogram obtained from the unconditioned ipsi reflex, independent of estrogen pretreatment. 5. In 12 out of 19 cases in which a contra cutaneous reflex was conditioned by a stimulus to the ipsi flank skin nerve (C-T 30 ms), the number of discharges in the early peak of the histogram was less than that in the early peak of the histogram derived from the unconditioned contra response, independent of estrogen pretreatment. 6. Intravenous injections of progesterone (P) or its metabolite 5 alpha-pregnane-3 alpha-ol-20-one (tetrahydraprogesterone, THP) decreased the magnitude of the early peak of the ipsi cutaneous reflex and the contra cutaneous reflex in LL, independent of estrogen pretreatment. At the same time, it did not reduce the magnitude of the early peak evoked by either ipsi or contra nerves after conditioning from the other side at C-T 30 ms. 7. As a consequence, the percentage facilitation of ipsi cutaneous reflexes by contra cutaneous conditioning was significantly increased after P or THP. This suggests that these steroids can selectively enhance behaviors involving bilateral inputs. 8. An unchanged axial motoneuron pool output to bilateral cutaneous inputs after P and THP, in spite of reduced motoneuron responses to cutaneous inputs from each side of the body, implies an increased gain in the reflex circuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Motor-unit recruitment in self-reinnervated muscle

1993 ◽  
Vol 70 (5) ◽  
pp. 1787-1796 ◽  
Author(s):  
T. C. Cope ◽  
B. D. Clark
Keyword(s):  
Nerve Stimulation ◽  
Sural Nerve ◽  
Motor Units ◽  
Cutaneous Reflexes ◽  
Nerve Section ◽  
Recruitment Pattern ◽  
Nerve Crush ◽  
Muscle Stretch ◽  
Physiological Properties ◽  
Recruitment Order

1. Recruitment order of motor units in self-reinnervated medial gastrocnemius (MG) muscles was studied in decerebrate cats 16 mo after surgical reunion of the cut MG nerve. Pairs of MG motor units were isolated by dual microelectrode penetration of ventral roots to measure their recruitment sequence during cutaneous reflexes in relation to their physiological properties. 2. Physiological properties of reconstituted motor units appeared normal, as expected. Also normal were the relationships among these properties: twitch and tetanic tension tended to increase with axonal conduction velocity and decrease with twitch contraction time. A small fraction of motor units (10/116) in reinnervated muscles produced either no measurable tension or unusually large amounts of tension compared with controls. This was the only distinct feature of the sample of reconstituted units. 3. In muscles reinnervated after nerve section, stretch was notably ineffective in eliciting reflex contraction of MG muscles or their constituent motor units (only 5/116 units). Incomplete recovery from nerve section was probably the cause of this impairment, because stretch reflexes were readily evoked in adjacent untreated muscles and in one reinnervated MG muscle that was studied 16 mo after nerve crush. In contrast with the ineffectiveness of muscle stretch, sural nerve stimulation succeeded in recruiting 49/116 units, a proportion fairly typical of normal MG muscles. 4. The contractions of the first unit recruited in cutaneous reflexes tended to be slower and less forceful than those of the other unit in a pair. By these measures, recruitment obeyed the size principle. This recruitment order with respect to unit contractile properties was not significantly different (P > 0.05) between untreated and reinnervated muscles but was significantly (P < 0.005) different from random order in both groups. The same recruitment pattern was observed for pairs of motor units sampled from the muscle reinnervated after nerve crush, whether units were recruited by muscle stretch or sural nerve stimulation. 5. The usual tendency for motor units with slower conduction velocity (CV) to be recruited in sural nerve reflexes before those with faster CV was not strong in reinnervated muscles. After nerve section the proportion of units exhibiting the usual recruitment pattern was not significantly different (P > 0.05) from a random pattern for CV. 6. The central finding is that the normal recruitment patterns recover from nerve injury in a muscle that is reinnervated by its original nerve. By contrast, stretch reflexes do not recover well from nerve section, and this deficiency may contribute to motor disability.

Modulation of Cutaneous Reflexes From the Foot During Gait in Parkinson's Disease

2010 ◽  
Vol 104 (1) ◽  
pp. 230-238 ◽  
Author(s):  
Jacques Duysens ◽  
Bart M. H. Van Wezel ◽  
Bouwien Smits-Engelsman
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Healthy Subjects ◽  
Biceps Femoris ◽  
Cutaneous Reflexes ◽  
Step Cycle ◽  
Reflex Responses ◽  
Cutaneous Reflex ◽  
Unsteady Gait ◽  
Fast Activation

Normal gait is characterized by a phase-dependent modulation of cutaneous reflexes. The role of the basal ganglia in regulating these reflexes is largely unknown. Therefore cutaneous reflex responses from the skin of the foot were studied during walking of patients with mild to moderate Parkinson's disease (PD). The reflex responses were elicited by stimulation of the sural nerve of the most affected leg. The responses were studied in the biceps femoris (BF) and tibialis anterior (TA) of both legs. The latencies, durations, and phase-dependent modulation patterns of the responses were mostly comparable with those observed in healthy subjects. However, on average the amplitude of the responses in the ipsilateral and contralateral BF was respectively 1.4- and 5-fold larger for the PD patients than that for the healthy subjects. This increase was mostly seen throughout the whole step cycle. However, in some PD patients the crossed BF responses were very large during the contralateral swing phase. In such cases the increase in crossed reflexes sometimes reflected premotoneuronal gating since it was not always due to increased background activation in that period. Fast activation of contralateral BF reflexes is known to occur in conjunction with ipsilateral perturbations when there is a threat to stability. It is concluded that cutanoeus reflexes are facilitated in PD but that some of the increase in reflexes in BF may be indirectly related to unsteady gait and to perceived instability.

scholarly journals Knee Angle Affects Posterior Chain Muscle Activation During an Isometric Test Used in Soccer Players

Sports ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 13 ◽  
Author(s):  
Paul James Read ◽  
Anthony Nicholas Turner ◽  
Richard Clarke ◽  
Samuel Applebee ◽  
Jonathan Hughes
Keyword(s):  
Muscle Activation ◽  
Gluteus Maximus ◽  
Biceps Femoris ◽  
Strength Test ◽  
Isometric Strength ◽  
Medial Gastrocnemius ◽  
Soccer Players ◽  
Emg Activity ◽  
Hamstring Muscle ◽  
Knee Angle

Background: It has been suggested that altering the knee flexion angle during a commonly used supine isometric strength test developed with professional soccer players changes preferential hamstring muscle recruitment. The aim of this study was to examine the electromyography (EMG) knee joint-angle relationship during this test, as these data are currently unknown. Methods: Ten recreational male soccer athletes (age: 28 ± 2.4 years) were recruited and performed a supine isometric strength test on their dominant leg with the knee placed at two pre-selected flexion angles (30° and 90°). The surface EMG of the gluteus maximus, biceps femoris, semitendinosus, and medial gastrocnemius was measured, in addition to the within-session reliability (intraclass correlation coefficient (ICC) and coefficient of variation (CV)). Results: Within-session reliability showed large variation dependent upon the test position and muscle measured (CV% = 8.8–36.1) Absolute mean EMG activity and percentage of maximum voluntary isometric contraction (MVIC) indicated different magnitudes of activation between the two test positions; however, significant mean differences were present for the biceps femoris only with greater activation recorded at the 30° knee angle (% MVIC: 31 ± 9 vs. 22 ± 7; p = 0.002). These differences (30% mean difference) were greater than the observed typical measurement error (CV% = 13.1–14.3 for the 90° and 30° test positions, respectively). Furthermore, the percentage MVIC showed a trend of heightened activation of all muscles with the knee positioned at 30°, but there was also more within-subject variation, and this was more pronounced for the gluteus maximus (CV% = 36.1 vs. 19.8) and medial gastrocnemius (CV% 31 vs. 22.6). Conclusions: These results indicate that biceps femoris and overall posterior chain muscle activation is increased with the knee positioned at 30° of flexion; however, the 90° angle displayed less variation in performance within individual participants, especially in the gluteus maximus and medial gastrocnemius. Thus, practitioners using this test to assess hamstring muscle strength should ensure appropriate familiarisation is afforded, and then may wish to prioritise the 30° knee position.

Adaptation of Cutaneous Stumble Correction When Tripping Is Part of the Locomotor Environment

2008 ◽  
Vol 99 (6) ◽  
pp. 2789-2797 ◽  
Author(s):  
Carlos Haridas ◽  
E. Paul Zehr ◽  
John E. Misiaszek
Keyword(s):  
Medial Gastrocnemius ◽  
Whole Body ◽  
General Nature ◽  
Cutaneous Reflexes ◽  
Step Cycle ◽  
Cutaneous Reflex ◽  
Postural Threat ◽  
Functional Relevance ◽  
Five Phases ◽  
Stimulation Of

We recently showed that cutaneous reflexes evoked by stimulating the superficial peroneal (SP; innervates foot dorsum) nerve are modulated according to the level of postural threat. Context-related modulation was observed mainly in contralateral (c) responses but not in the ipsilateral responses. This lack of effect on ipsilateral (i) cutaneous reflexes might have been caused by the general nature of the whole body perturbation. We therefore hypothesized that context-relevant mechanical perturbations applied to the dorsum of the foot by an instrumented rod at early swing during walking would produce differences in ipsilateral cutaneous reflex amplitudes, consistent with the functional relevance of the SP nerve in stumble correction responses. Subjects walked on a motorized treadmill under four conditions: 1) normal, 2) normal with mechanical perturbations at the foot dorsum, 3) arms crossed, and 4) arms crossed with mechanical perturbations at the foot dorsum. Electrical stimulation of the SP nerve was delivered at five phases of the step cycle, and cutaneous reflexes were compared between all conditions for each phase of the step cycle. Reflex responses were generally found to be modulated in amplitude during walking conditions in which mechanical perturbations were delivered, particularly in ipsilateral tibialis anterior (iTA), which showed a marked reduction in inhibition. The results indicated cutaneous reflexes in iTA and contralateral medial gastrocnemius (cMG) were influenced by the threat of a trip, induced by applying mechanical perturbations to the foot dorsum during walking. This task-related gating of cutaneous reflexes was not generalized to all muscles, thus suggesting a functional role in the maintenance of stability during locomotion.

scholarly journals Aβ Fibers Mediate Cutaneous Reflexes During Human Walking

2000 ◽  
Vol 83 (5) ◽  
pp. 2980-2986 ◽  
Author(s):  
B.M.H. van Wezel ◽  
B.G.M. van Engelen ◽  
F.J.M. Gabreëls ◽  
A.A.W.M. Gabreëls-Festen ◽  
J. Duysens
Keyword(s):  
Healthy Subjects ◽  
Biceps Femoris ◽  
Human Gait ◽  
Emg Activity ◽  
Cutaneous Reflexes ◽  
Step Cycle ◽  
Reflex Responses ◽  
Low Threshold ◽  
Two Phases ◽  
Aβ Fibers

During human gait, transmission of cutaneous reflexes from the foot is controlled specifically according to the phase of the step cycle. These reflex responses can be evoked by nonnociceptive stimuli, and therefore it is thought that the large-myelinated and low-threshold Aβ afferent fibers mediate these reflexes. At present, this hypothesis is not yet verified. To test whether Aβ fibers are involved the reflex responses were studied in patients with a sensory polyneuropathy who suffer from a predominant loss of large-myelinated Aβ fibers. The sural nerve of both patients and healthy control subjects was stimulated electrically at a nonnociceptive intensity during the early and late swing phases while they walked on a treadmill. The responses were studied by recording electromyographic (EMG) activity of the biceps femoris (BF) and tibialis anterior (TA) of the stimulated leg. In both phases, large facilitatory responses were observed in the BF of the healthy subjects. These facilitations were reduced significantly in the BF of the patients, indicating that Aβ fibers mediate these reflexes. In TA similar results were obtained. The absolute response magnitude across the two phases was significantly smaller for the patients than for the healthy subjects. The TA responses for the healthy subjects were on average facilitatory during early swing and suppressive during end swing. Both facilitations and suppressions were considerably smaller for the patients, indicating that both types of responses are mediated by Aβ fibers. It is concluded that low-threshold Aβ sensory fibers mediate these reflexes during human gait. The low threshold and the precise phase-dependent control of these responses suggest that these responses are important in the regulation of gait. The loss of such reflex activity may be related to the gait impairments of these patients.

scholarly journals Bipedal reflex coordination to tactile stimulation of the sural nerve during human running

1995 ◽  
Vol 73 (5) ◽  
pp. 1947-1964 ◽  
Author(s):  
A. A. Tax ◽  
B. M. Van Wezel ◽  
V. Dietz
Keyword(s):  
Sural Nerve ◽  
Elementary Property ◽  
Emg Activity ◽  
Reflex Modulation ◽  
Step Cycle ◽  
Perception Threshold ◽  
Reflex Responses ◽  
Cutaneous Reflex ◽  
Human Running ◽  
Stimulation Of

1. Cutaneous reflex responses were elicited during human running (8 km/h) on a treadmill by electrical stimulation of the sural nerve at the ankle. Stimulus trains (5 pulses of 1 ms at 200 Hz) at three nonnociceptive intensities, which were 1.5, 2.0, and 2.5 times perception threshold (PT), were delivered at 16 phases of the step cycle. For 11 subjects the surface electromyographic (EMG) activity of both the ipsilateral and contralateral long head of the biceps femoris (iBF and cBF, respectively), the semitendinosus (iST and cST), the rectus femoris (iRF and cRF), and the tibialis anterior (iTA and cTA) were recorded. 2. During human running nonnociceptive sural nerve stimulation appears to be sufficient to elicit large, widespread and statistically significant reflex responses, with a latency of approximately 80 ms and a duration of approximately 30 ms. These reflex responses seem to be an elementary property of human locomotion. This is indicated by the occurrence of the responses in all subjects, the consistency of most of the reflex patterns across the subjects and, apart from a small amount of habituation, the reproducibility of the responses during the course of the experiment. 3. The responses are modulated continuously throughout the step cycle such that their magnitude does not in general covary with the background locomotor activities. This is observed most clearly in iST, iTA, and cTA for which statistically significant reflex reversals are demonstrated, and in cRF and cTA for which the responses are gated during most of the step cycle. 4. The response magnitude generally increases as a function of increasing intensity, whereas the phase-dependent reflex modulation is intensity independent. 5. A functional dissociation within the ipsilateral hamstring muscles is demonstrated: the iBF and iST show an antagonistic reflex pattern (facilitatory and suppressive, respectively) during the periods of synergistic background locomotor activity in the step cycle. Contralaterally, however, the cBF and cST are reflexively activated as close synergists during these periods. 6. The reflex responses and their phase-dependent modulation are different for the homologous muscles in the two legs. Yet, some similarities are observed. These are present rather with respect to the phase of the corresponding leg than with respect to the phase of the stimulated leg. Both observations suggest that the phase-dependent reflex modulation is controlled separately in the ipsilateral and contralateral legs. 7. The response simultaneity in all investigated muscles supports the notion of a coordinated cutaneous interlimb reflex during human running.(ABSTRACT TRUNCATED AT 400 WORDS)

Asymmetry of Hindlimb Muscle Activity and Cutaneous Reflexes After Tendon Transfers in Kittens

1999 ◽  
Vol 82 (6) ◽  
pp. 3392-3405 ◽  
Author(s):  
G. E. Loeb
Keyword(s):  
Muscle Activity ◽  
Central Pattern Generators ◽  
Mechanical Action ◽  
Emg Activity ◽  
Sham Operation ◽  
Cutaneous Reflexes ◽  
Tendon Transfers ◽  
Cutaneous Reflex ◽  
Hindlimb Muscle ◽  
Pattern Generators

The mechanical actions of various ankle muscles were changed by surgically crossing or transferring the tendons in kittens. After the kittens grew to adults, both hindlimbs were implanted with multiple electromyogram (EMG) recording and cutaneous nerve stimulation electrodes to compare the activity of altered and normal muscles. The tendon transfers showed a remarkable tendency to regrow toward normal or only slightly altered mechanical action. In these animals and in the sham-operation controls, the patterns of muscle activity and reflexes were symmetrical in corresponding muscles of the two legs, although they could differ substantially between animals, particularly for the cutaneous reflexes. Eleven animals had at least some persistent alterations in muscle action. Their cutaneous reflex patterns tended to be asymmetric, in some cases quite markedly. EMG activity during unperturbed locomotion and paw-shaking was more symmetrical, but there were some changes in altered muscles and their synergists. The central pattern generators for locomotion and paw-shaking and particularly for cutaneous reflexes during locomotion appear to be at least partially malleable rather than entirely hardwired. This may provide a tool for studying their development and spinal plasticity in general.

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