Sensory Control of Locomotion: Reflexes Versus Higher-Level Control (original) (raw)
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Forelimb movements contribute to hindlimb cutaneous reflexes during locomotion in cats
bioRxiv (Cold Spring Harbor Laboratory), 2024
During quadrupedal locomotion, central circuits interacting with somatosensory feedback coordinate forelimb and hindlimb movements. How this is achieved is not clear. To determine if forelimb movements modulate hindlimb cutaneous reflexes involved in responding to an external perturbation, we stimulated the superficial peroneal nerve in six intact cats during quadrupedal locomotion and during hindlimb-only locomotion (with forelimbs standing on stationary platform) and in two spinal-transected cats during hindlimb-only locomotion. We compared cutaneous reflexes evoked in six ipsilateral and four contralateral hindlimb muscles. Results showed similar occurrence and phase-dependent modulation of short-latency inhibitory and excitatory responses during quadrupedal and hindlimb-only locomotion in intact cats. However, the depth of modulation was reduced in the ipsilateral semitendinosus during hindlimb-only locomotion. Additionally, longer-latency responses occurred less frequently in extensor muscles bilaterally during hindlimb-only locomotion while short-latency inhibitory and longer-latency excitatory responses occurred more frequently in the ipsilateral and contralateral sartorius anterior, respectively. After spinal transection, short-latency inhibitory and excitatory responses were similar to both intact conditions, while mid-or longer-excitatory responses were reduced or abolished. Our results suggest that the absence of forelimb movements suppresses inputs from supraspinal structures and/or cervical cord that normally contribute to longer-latency reflex responses in hindlimb extensor muscles. NEW & NOTEWORTHY During quadrupedal locomotion, the coordination of forelimb and hindlimb movements involves central circuits and somatosensory feedback. To demonstrate how forelimb movement affects hindlimb cutaneous reflexes during locomotion, we stimulated the superficial peroneal nerve in intact cats during quadrupedal and hindlimb-only locomotion, as well as in spinal-transected cats during hindlimb-only locomotion. We show that forelimb movement influences the modulation of hindlimb cutaneous reflexes, particularly the occurrence of long-latency reflex responses.
Contribution of stretch reflexes to locomotor control: a modeling study
Biological Cybernetics, 2004
It is known that the springlike properties of muscles provide automatic load compensation during weight bearing. How crucial is sensory control of the motor output given these basic properties of the locomotor system? To address this question, a neuromuscular model was used to test two hypotheses. (1) Stretch reflexes are too weak and too delayed to contribute significantly to weight-bearing. (2) The important contributions of sensory input involve state-dependent processing. We constructed a two-legged planar locomotor model with 9 segments, driven by 12 musculotendon actuators with Hill-type force-velocity and monotonic force-length properties. Electromyographic (EMG) profiles of the simulated muscle groups during slow level walking served as actuator activation functions. Spindle Ia and tendon organ Ib sensory inputs were represented by transfer functions with a latency of 35 ms, contributing 30% to the net EMG profile and gated to be active only when the receptor-bearing muscles were contracting. Locomotor stability was assessed by parametric variations of actuator maximum forces during locomotion in open-loop (“deafferented”) trials and in trials with feedback control based on either sensory-evoked stretch reflexes or finite-state rules. We arrived at the following conclusions. (1) In the absence of sensory control, the intrinsic stiffness of limb muscles driven by a stereotyped rhythmical pattern can produce surprisingly stable gait. (2) When the level of central activity is low, the contribution of stretch reflexes to load compensation can be crucial. However, when central activity provides adequate load compensation, the contribution of stretch reflexes is less significant. (3) Finite-state control can greatly extend the adaptive capability of the locomotor system.
A reappraisal of reflex stepping in the cat
The Journal of physiology, 1969
1. In re-evaluating Sherrington's experiment in which deafferented muscles in decerebrated cats ;stepped', we recorded from L5 ventral roots, a chief supplier of the major extensors of the hind legs, during stimulation of the common peroneal nerves. The extensor muscles had been denervated by appropriate dorsal root sections; the cats had been paralysed with a neuromuscular blocking agent.2. Response versus interval curves were constructed using 1 Hz stimulation. When stimulation of one peroneal preceded another, the responses ipsilateral to the second stimulation were facilitated at testing intervals of -2 to 10 msec, and inhibited at intervals of 30-400 msec.3. Responses from the L5 ventral roots mimicked ;stepping', waxing and waning at 1 Hz, only when 1 Hz was the best frequency for stimuli delivered to the two common peroneals (e.g. 24 and 25 Hz). When both sides were stimulated at the same frequency, no periodic changes in response amplitudes were seen.4. It was co...
Physical therapy, 1972
Twenty cats were decerebrated by intercollicular section to produce hyperactive stretch reflexes similar to those found in patients with spasticity. Simultaneous recordings were made of electrical activity from the soleus and tibialis anterior muscles and of ankle joint movement during the flexion response elicited by cutaneous stimulation. Three types of responses were recorded from the antagonistic soleus muscle: I) a short latency twitch elicited by the mechanical stretch from dorsiflexion; 2) a long latency tetanic rebound (120-240 msec post stimulation) initiated by cutaneous afferents, and 3) a twitch coincident with that of the tibialis anterior, for which contributing factors were not delineated. Changing ankle joint position modified these responses. When soleus electrical activity was continuous and intense, the periods of evoked inhibition were markedly reduced. Olinical observation of patients with hyperactive stretch reflexes has raised the question of the influence of these reflexes on voluntary motion. In the patient with spasticity, the lower threshold of the motoneuron may alter reciprocal interaction, Miss Sahrmann is a Ph.D. candidate,
Corticospinal control of locomotor pathways generating extensor activities in the cat
Experimental Brain Research, 2001
Interneuronal convergence of corticospinal and segmental pathways involved with the generation of extensor activities during locomotion was investigated in decerebrate and partially spinalized cats. L-dihydroxyphenylalanine (L-DOPA) was slowly injected until long-latency, long-lasting discharges could be evoked by the stimulation of contralateral flexor reflex afferents (coFRA) and the group I autogenetic inhibition was reversed to polysynaptic excitation in extensor motoneurons. Under these conditions, we stimulated in alternation the contralateral pyramidal tract (PT), group I afferents from knee and ankle extensor muscles, and both stimuli together. We did the same for the stimulation of PT and of coFRA. Clear polysynaptic EPSPs could be evoked from all three sources in 32 extensor motoneurons. Convergence was inferred from spatial facilitation, which occurred when the amplitude of the EPSPs evoked by the combined stimuli was notably larger than the algebraic sum of the EPSPs evoked by individual stimulation. Spatial facilitation was found between PT and extensor group I inputs in 30/59 tests (51%) in 20 motoneurons and in all cases (6/6) between PT and coFRA in six motoneurons. When fictive locomotion was induced with further injection of L-DOPA, PT descending volleys from the same stimulating site could reset the stepping rhythm by initiating bursts of activity in all extensors. These results indicate that at least some of the corticospinal fibers project onto interneurons shared by the coFRA and the polysynaptic excitatory group I pathways to extensors. The implications of such convergence patterns on the organization of the extensor "halfcenter" for locomotion are discussed.
eneuro
Coordinating the four limbs is an important feature of terrestrial mammalian locomotion. When the foot dorsum contacts an obstacle, cutaneous mechanoreceptors send afferent signals to the spinal cord to elicit coordinated reflex responses in the four limbs to ensure dynamic balance and forward progression. To determine how the locomotor pattern of all four limbs changes in response to a sensory perturbation evoked by activating cutaneous afferents from one hindlimb, we electrically stimulated the superficial peroneal (SP) nerve with a relatively long train at four different phases (mid-stance, stance-to-swing transition, mid-swing, and swing-to-stance transition) of the hindlimb cycle in seven adult cats. The largest functional effects of the stimulation were found at mid-swing and at the stance-to-swing transition with several changes in the ipsilateral hindlimb, such as increased activity in muscles that flex the knee and hip joints, increased joint flexion and toe height, increas...
Ia afferent activity during a variety of voluntary movements in the cat
The Journal of physiology, 1977
1. Implanted dorsal root electrodes were used to record discharge trains of single spindle primary afferents (Ia's) of the cat's hind limb during different types of movement.2. The length of the ipsilateral ankle extensors was continuously monitored by an implanted length gauge. Length changes occurring during active stepping were subsequently passively reproduced during brief anaesthesia.3. A comparison of the Ia responses in active and simulated step cycles revealed that moderate fusimotor drive to ankle extensor spindles probably occurred mainly, if not exclusively, during the E(1), E(2) and E(3) phases of active stepping.4. A temporal advance in the Ia response to passive stretching in the F-phase was attributed to the after-effects of fusimotor activity in the extension phases.5. Light thrust applied to the animal's back evoked a potent fusimotor response. This load compensation effect may provide an explanation for the apparently higher degree of alpha-gamma co-act...
Phasic gain control of reflexes from the dorsum of the paw during spinal locomotion
Brain Research, 1977
In chronic spinal cats walking with their hindlimbs on a treadmill belt, tactile stimuli were applied to the dorsum of the paw during various phases of the step cycle. A stimulation during the swing phase evoked a flexion response with a concomitant crossed extension, whereas in stance it induced an increased ipsilateral extension. EMG-recordings show short latency reflex responses in flexors and extensors, respectively. The responses are organized such that latencies of knee muscles are shorter than those of ankle and hip muscles. The movements induced by the stimulations appear to be very meaningful during normal conditions in compensating for any unpredicted obstacle disturbing the movement of the paw during locomotion. Responses during forward flexion and during the support phase are well adapted to the ongoing locomotor activity and do not influence the interlimb coordination whereas a stimulation when the foot approaches the ground after the end of flexion disturbs the regular alternating pattern. Different possible mechanisms underlying this phasedependent reflex reversal are discussed.