Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Locomotion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources
PubMed2004

An adaptive, self-organizing dynamical system for hierarchical control of bio-inspired locomotion.

In this paper, dynamical systems made up of locally coupled nonlinear units are used to control the locomotion of bio-inspired robots and, in particular, a simulation of an insect-like hexapod robot. These controllers are inspired by the biological paradigm of central pattern generators and are responsible for generating a locomotion gait. A general structure, which is able to change the locomotion gait according to environmental conditions, is introduced. This structure is based on an adaptive system, implemented by motor maps, and is able to learn the correct locomotion gait on the basis of a reward function. The proposed control system is validated by a large number of simulations carried out in a dynamic environment for simulating legged robots.

Adaptation, Physiological↗
PubMed2003

The role of locomotion in the acquisition and transfer of spatial knowledge in children.

The role of locomotion in the acquisition and transfer of spatial knowledge was investigated in 144 five-, seven- and eleven-year-old children. Two experiments were conducted in the Kiel locomotor maze. In the first experiment, one group of children explored the spatial layout by walking through the maze, while another learned the maze by surveying the layout. In the second experiment, children were exposed to one of two orientation tests in the maze, one of which could be solved using "landmark orientation", the other only using a "relational place orientation". Children sitting by the side of the experimental chamber surveying the maze needed fewer trials to learn the spatial layout than children exploring the environment in the locomotion condition, but in the orientation test demanding the "relational place orientation" children who had explored the maze in the locomotion condition outperformed the children in the non-locomotion condition. Results are discussed in the context of cognitive mapping models.

Child↗
PubMed2000

Patterns of fusimotor activity during locomotion in the decerebrate cat deduced from recordings from hindlimb muscle spindles.

1. Recordings have been made from multiple single muscle spindle afferents from medial gastrocnemius (MG) and tibialis anterior (TA) muscles of one hindlimb in decerebrate cats, together with ankle rotation and EMG signals, during treadmill locomotion. Whilst the other three limbs walked freely, the experimental limb was denervated except for the nerves to MG and TA and secured so that it could rotate only at the ankle joint, without any external load. Each afferent was characterised by succinylcholine testing with regard to its intrafusal fibre contacts. Active movements were recorded and then replayed through a servo mechanism to reproduce the muscle length changes passively after using a barbiturate to suppress gamma-motor firing. 2. The difference in secondary afferent firing obtained by subtracting the discharge during passive movements from that during active movements was taken to represent the profile of static fusimotor activity. This indicated an increase before the onset of movement followed by a strongly modulated discharge in parallel with muscle shortening during locomotion. The pattern of static firing matched the pattern of unloaded muscle shortening very closely in the case of TA and with some phase advance in the case of MG. The same effects were observed in primary afferents. 3. Primary afferents with bag1 (b1) contacts in addition showed higher firing frequencies during muscle lengthening in active than in passive movements. This indicated increased dynamic fusimotor firing during active locomotion. There was no evidence as to whether this fluctuated during the movement cycles. 4. When the mean active minus passive difference profile of firing in bag2-chain (b2c) type primary afferents was subtracted from that for b1b2c afferents, the difference was dominated by a peak centred on the moment of maximum lengthening velocity (v). 5. The component of the active minus passive difference firing due to b1 fibre contacts could be modelled by f(t) = av (where a is a constant) during lengthening and by f(t) = 0.2 av during shortening. The remainder of the difference signal matched the predictions of the static fusimotor signal derived from secondary afferents. 6. The findings are discussed in relation to the concept that the modulated static fusimotor pattern may represent a 'temporal template' of the expected movement, though the relationship of the results to locomotion in the intact animal will require further investigation. The analysis of the data indicates that the combined action of muscle length changes and static and dynamic fusimotor activity to determine primary afferent firing can be understood in terms of the interaction between the b1 and b2c impulse initiation sites.

Animals↗
PubMed1988

Lumbar back muscle activity during locomotion: effects of voluntary modifications of normal trunk movements.

The mechanisms of adaptation of the trunk to changed mechanical conditions were studied during locomotion in man. The myoelectrical (EMG) activity in lumbar back muscles and the movements of the trunk were recorded in nine healthy subjects during walking and running on a motor-driven treadmill. Two different types of voluntary modifications of the movement pattern were used: (1) The trunk was kept in an extreme forward or backward tilted position. In both these situations the basic EMG pattern with two periods of activity per stride cycle was maintained during walking, whereas a major shift relative to the stride cycle (25% of the stride cycle duration) occurred in running with the trunk tilted backwards. The synchrony of the back muscle activation at both sides increased when locomotion was performed with the trunk tilted forwards. The relative duration of the EMG bursts was similar to normal locomotion and corresponded to 15-26% of the stride cycle duration in walking and 23-37% in running. (2) In the other type of modification the subjects were instructed to exaggerate the angular trunk movements either in the sagittal or in the frontal plane. The basic EMG pattern and phase relationships remained in most cases unchanged. One exception was running with exaggerated lateral movements, in which only one period of back muscle activity per stride cycle was observed. The relative duration of the bursts was longer in trials with exaggerated trunk movements as compared to normal locomotion. In walking and running with the trunk tilted forwards or backwards the lumbar back muscles were not always involved as prime movers of the trunk. This was in contrast to the more dynamic situations, in which the back muscle activity appeared to be directly involved in braking and reversing the exaggerated trunk movements.

Adaptation, Physiological↗
PubMed1998

Initiation of locomotion in mammals.

Several "locomotor regions" of the mammalian brain stem can be stimulated, either electrically or chemically, to induce locomotion. Active cells labeled with c-fos within the mesencephalic locomotor region (MLR) have been found in the periaqueductal gray, the cuneiform nucleus, the pedunculopontine nucleus, and the locus coeruleus. Different subsets of these nuclei appear to be activated during locomotion produced in different behavioral contexts. The locomotor nuclei can be classified into areas associated with exploratory, appetitive, and defensive locomotion, in accordance with the proposal of Sinnamon (1993, Prog. Neurobiol. 41: 323-344). The interpretation of lesion studies designed to reveal areas of the brain essential for locomotion must be based on knowledge of the nuclei which become active in the specific locomotor task being tested. An argument is put forward in favor of the continued use of the term "mesencephalic locomotor region."

Animals↗
PubMed1982

Modulation of stretch reflexes during locomotion in the mesencephalic cat.

1. A cat preparation was used to study the modulation of stretch reflexes during locomotion. The brain stem was transected and locomotion was induced by electrical stimulation of the mesencephalic locomotor region below the level of transection. Three legs walked normally on a treadmill, while the fourth leg, which was denervated except for the soleus muscle, was held fixed. Brief length perturbations were applied to the soleus muscle at various phases of the stepping cycle.2. The stretch reflex in this muscle was deeply modulated during the step cycle, and reached its peak at or before the peak in soleus e.m.g. activity associated with the locomotion. A similar variation was observed when the sciatic nerve was stimulated electrically at a strength which elicited reflex activity (H wave), but did not directly elicit motor nerve activity (M wave). Variation in the reflex during electrical stimulation could not be accounted for by cyclic variation in fusimotor activity or in the afferent volley, but must be due to post-synaptic changes in alpha-motoneurones or in the presynaptic inputs to them.3. Large changes were also observed in intrinsic muscle stiffness during the step cycle. The maximum stiffness occurred near the time the limb would normally strike the ground during locomotion. A high stiffness would be useful in reducing the amount that the limb would yield under the weight of the body during the extension phase of the step cycle. The variation of the stretch reflex in parallel with stiffness suggests that reflexes could assist in this load compensation. The variation is not consistent with the idea that the stretch reflex is used to compensate for changes in intrinsic muscle properties, so that the total system behaves more like a spring of constant stiffness than does muscle alone.

Animals↗
PubMed1984

Discharges of nucleus interpositus neurones during locomotion in the cat.

Extracellular recordings were made from ninety-five cerebellar nuclear neurones in the cat. All were studied during periods of steady walking at 0.5 m/s and most were also studied in the resting animal. Most neurones were in nucleus interpositus anterior; forty-four cells were shown by antidromic invasion to project to the mid-brain. Most neurones discharged tonically in the absence of overt movements and the mean rate was 42 impulses/s (S.D. +/- 23). During locomotion the mean rate was 68 impulses/s (S.D. +/- 32). In all but seven neurones the discharge during locomotion was frequency modulated but in different neurones the depth of modulation varied from 5 to 161 impulses/s (mean 52 impulses/s; S.D. +/- 30) and the time of peak discharge relative to the step cycle in the ipsilateral forelimb also varied widely. Despite the individual differences the population as a whole was much more active during forelimb swing than during stance, both in numbers of neurones strongly active and in over-all average discharge rate (74 impulses/s as compared with 55). Most neurones had tactile receptive fields on the ipsilateral forelimb while others received input from head and neck or from both ipsilateral limbs. The tendency to discharge preferentially during early swing was greatest for the first group, especially the subpopulations with receptive fields around or proximal to the elbow. Cells encountered in close sequence during a micro-electrode track had similarly located receptive fields and usually showed similar patterns of discharge during locomotion. These findings are discussed in relation to the suggestion by Orlovsky (1972a, b, c) that nucleus interpositus assists in regulating locomotion by evoking rubrospinal discharges which facilitate the flexor muscle activities produced by the spinal mechanisms responsible for generating the swing phase of the step cycle.

Action Potentials↗
PubMed1988

Evidence that mid-lumbar neurones in reflex pathways from group II afferents are involved in locomotion in the cat.

1. A group of interneurons in the mid-lumbar segments of the cat spinal cord which mediate disynaptic excitation or inhibition of motoneurones from group II muscle afferents have recently been described. To test the possibility that the activity of these interneurones is related to the activity in the neuronal networks which subserve locomotion we have investigated whether they are influenced by two procedures which can induce locomotion. These procedures were electrical stimulation within the cuneiform nucleus (the 'mesencephalic locomotor region') in anaesthetized preparations and systemic administration of 3,4-dihydroxyphenylalanine (DOPA) in decerebrate, spinalized, unanaesthetized preparations. The interneurones we have tested were located in the fourth lumbar (L4) segment and were excited by group II muscle afferents; more than half of them were antidromically activated from the hindlimb motor nuclei. 2. Stimuli applied in the cuneiform nucleus evoked excitatory postsynaptic potentials (EPSPs) in a high proportion of these interneurones. The stimuli also evoked distinct extracellular field potentials in the ventral horn of the L4 segment. The properties and latencies of both the intra- and extracellularly recorded potentials show that they were evoked disynaptically, via supraspinally located relay neurones and a fast-conducting descending tract. 3. Stimulation of the cortico- and rubrospinal tracts excited or inhibited some of the L4 neurones, often at latencies suggesting mono- or disynaptic coupling. The neurones which appeared to be monosynaptically excited from the cortico- and rubrospinal tracts tended to be located dorsal to the neurones which were activated from the cuneiform nucleus. 4. Systemic administration of DOPA depressed the responses evoked by stimulation of group II afferents of L4 interneurones which projected to motor nuclei. DOPA also depressed extracellular field potentials evoked by group II afferents in the intermediate zone and in the ventral horn (at the location of the interneurones) but hardly affected those in the dorsal horn. 5. By showing that both stimulation in the cuneiform nucleus and the administration of DOPA influence activity of L4 interneurones which are excited by group II afferents and which project to motor nuclei, the results of this study support the hypothesis that these neurones are in some way involved in locomotion. However, the opposing effects of DOPA administration and of stimulation in the cuneiform nucleus make the interpretation of their role in locomotion rather difficult before it is known to what extent they are active throughout the step cycle.

Action Potentials↗
PubMed1996

Group I extensor afferents evoke disynaptic EPSPs in cat hindlimb extensor motorneurones during fictive locomotion.

1. Intracellular recording from extensor motoneurones in paralysed decerebrate cats was used to examine the distribution of short-latency non-monosynaptic excitation by group I afferents during fictive locomotion produced by stimulation of the mesencephalic locomotor region (MLR). 2. During the extension but not the flexion phase of fictive locomotion, stimulation of ankle extensor nerves at 1.2-2.0 times threshold evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating hip, knee and ankle extensors. Disynaptic EPSPs were also evoked by selective activation of group Ia muscle spindle afferents by muscle stretch. 3. The central latencies of these group I-evoked EPSPs (mean, 1.55 ms) suggest their mediation by a disynaptic pathway with a single interneurone interposed between extensor group I afferents and extensor motoneurones. Disynaptic EPSPs were also evoked during periods of spontaneous locomotion following the cessation of MLR stimulation. 4. Hip extensor motoneurones received disynaptic EPSPs during extension following stimulation of both homonymous and ankle extensor nerves. Stimulation of hip extensor nerves did not evoke disynaptic EPSPs in ankle extensor motoneurones. 5. The appearance of disynaptic EPSPs during extension appears to result from cyclic disinhibition of an unidentified population of excitatory spinal interneurones and not postsynaptic voltage-dependent conductances in motoneurones or phasic presynaptic inhibition of group I afferents during flexion. 6. The reorganization of group I reflexes during fictive locomotion includes the appearance of disynaptic excitation of hip, knee and ankle extensor motoneurones. This excitatory reflex is one of the mechanisms by which group I afferents can enhance extensor activity and increase force production during stance.

Afferent Pathways↗
PubMed1991

EMG patterns of rat ankle extensors and flexors during treadmill locomotion and swimming.

Intramuscular electromyography (EMG) was used to determine and compare the recruitment patterns of the rat soleus (Sol), tibialis anterior (TA), and a deep and a superficial portion of the medial gastrocnemius (MG) during treadmill locomotion at various speeds and inclines and during swimming. Raw EMG signals for 10-20 step or stroke cycles were rectified, averaged, and processed to determine cycle period (EMG onset of one cycle to EMG onset of the next cycle), EMG burst duration, and integrated area of the rectified burst (IEMG). Mean EMG per burst was calculated as IEMG/burst duration. IEMG/min was calculated as IEMG times the number of bursts (cycles) per minute. Cycle period and burst duration of the extensors decreased hyperbolically, while the TA burst duration was unchanged, with increased treadmill speed. With increased treadmill speed, IEMG was decreased in the Sol and unchanged in the MG and TA, whereas IEMG/min decreased in the Sol and increased in the MG and TA. An elevation in treadmill incline resulted in an increase in the activation levels of the MG but not in the Sol or TA. These data indicate that the additional power required at increased speeds and/or inclines of treadmill locomotion is derived from the recruitment of the fast extensors, e.g., the MG. The mean cycle period during swimming was similar to that observed during the fastest treadmill locomotion. EMG burst durations and amplitudes, however, were higher in the TA, relatively similar in the MG, and lower in the Sol during swimming than treadmill locomotion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Phenyl biguanide does not inhibit locomotion in conscious rabbits.

Stimulation of cardiopulmonary vagal C fibers with phenyl biguanide (PBG) reflexly inhibits locomotion in addition to causing depression of blood pressure (BP), heart rate (HR), and respiration in cats and rats. We investigated whether PBG caused somatomotor inhibition during exercise in the rabbit, a species in which it is known that the hemodynamic and respiratory responses to PBG are mediated by cardiac rather than by pulmonary receptors. In eight New Zealand White rabbits, BP, HR, and hindlimb electromyographic (EMG) responses to 60 and 120 micrograms/kg PBG and saline vehicle were evaluated during two separate 3-min exercise bouts at 10 m/min at 0% grade. During exercise, 60 micrograms/kg PBG decreased BP (-27 +/- 4 mmHg) and HR (-95 +/- 16 beats/min) but did not inhibit locomotion as suggested by the EMG response (+112 +/- 8% of preinfusion EMG). Hemodynamic and EMG responses to 120 micrograms/kg PBG were similar to 60 micrograms/kg PBG. Saline infusion during exercise had no effect on HR, BP, or locomotion (+114 +/- 8% of preinfusion EMG). Locomotion is not inhibited by PBG in rabbits, which suggests that PBG-induced reflex somatomotor inhibition observed in other species is primarily mediated by pulmonary rather than by cardiac receptors.

Animals↗
PubMed2001

Neck muscle vibration disrupts steering of locomotion.

Neck muscle vibration was applied to human subjects to assess the influences of neck abnormal proprioceptive input on the organization and execution of gait. Subjects walked blindfolded to a previously seen target, located straight ahead at ~4 m. Vibration was applied on the right side of the neck, both during and before walking. The variables measured were length, duration, and velocity of trajectory; relative and absolute frontal errors at target; and width of walking support base. Vibration applied during locomotion produced an undershoot of target and deviation of gait trajectory toward the side opposite to vibration. Vibration applied before locomotion produced no effect on length of trajectory but slowing of velocity and nonsystematic deviation. When vibration frequency was increased, the amplitude of the nonsystematic deviation increased. Vibration applied during or before stance trials had minor effects on body sway. Vibration before stance had no effect on the position of mean center of foot pressure, whereas vibration during stance displaced it to the side opposite to the vibrated muscle. We suggest that vibration during locomotion reduces length and velocity of trajectory because of a direct action on the locomotor centers and produces trajectory deviation related to its effect on stance. Vibration before locomotion causes a major, nonsystematic deviation from the planned trajectory, possibly connected to a disorientation of the internal references.

Adult↗
PubMed2005

Intracellular analysis of reflex pathways underlying the stumbling corrective reaction during fictive locomotion in the cat.

In cat and humans, contact between an obstacle and the dorsum of the foot evokes the stumbling corrective reaction (reflex) that lifts the foot to avoid falling. This reflex can also be evoked by short trains of stimuli to the cutaneous superficial peroneal (SP) nerve in decerebrate cats during the flexion phase of fictive locomotion. Here we examine intracellular events in hindlimb motoneurons accompanying stumbling correction. SP stimulation delivered during the flexion phase excites knee flexor motoneurons at short latency [minimum excitatory postsynaptic potential (EPSP) latency 1.8 ms; mean 2.7 ms]. Although a similar short latency excitation occurs in ankle extensors (mean latency, 2.8 ms), recruitment is delayed until successive shocks in the stimulus train overcome the locomotor-related hyperpolarization of ankle extensors. In ankle flexor motoneurons, SP stimulation evokes an inhibition (mean latency, 2.7 ms) that briefly reduces or stops their firing during the flexion phase. There is a phase-dependent modulation of SP-evoked EPSP amplitude as well as latency during locomotion. However, the more obvious change in SP reflex pathways with the onset of fictive locomotion is the reduced inhibition of ankle extensor motoneurons and the increased inhibition of ankle flexors. These results show that the characteristic pattern of hindlimb motoneuron activation during SP nerve-evoked stumbling correction results from 1) di- and trisynaptic excitation of knee flexor and ankle extensor motoneurons; 2) increased inhibitory postsynaptic potentials in ankle flexors and a suppression of inhibition in extensors, 3) sculpting of the short-latency SP postsynaptic effects by motoneuron membrane potential, and 4) longer latency excitatory effects that are likely evoked by lumbar interneurons involved in the generation of fictive locomotion.

Animals↗
PubMed1987

Climbing fiber afferent modulation during treadmill locomotion in the cat.

The relationship of the climbing fiber afferent discharge to the unperturbed and perturbed step cycle was evaluated in the cat. Following a precollicular-premamillary decerebration, cats walked spontaneously on a motorized treadmill. Purkinje cells were recorded extracellularly and simple and complex spikes were discriminated. Right forelimb displacement, biceps and triceps EMG activity, as well as treadmill velocity, were also monitored. In some animals pressure measurements of the contact of the footpad with the treadmill were obtained. Cells were studied during both "normal" and perturbed locomotion. The perturbation consisted of a braking of the treadmill at different phases in the step cycle. Histograms of the simple and complex spike activity, and averages of the right forelimb displacement, biceps, and triceps EMG activity and treadmill velocity were constructed. The complex spike activity of 163 Purkinje cells was averaged through a minimum of 50 sweeps in either normal and/or perturbed locomotion. Statistical analysis revealed that the probability of the climbing fiber afferent discharge in 54% of the cells (36/67) studied during normal locomotion was significantly modulated with the step cycle. For most Purkinje cells the onset of the increase in climbing fiber afferent discharge was coupled to triceps activity and the onset of stance phase. A group of cells exhibited complex spike discharge in association with biceps onset and swing. These observations suggest that complex spike discharge occurs preferentially at the phase transition periods in the step cycle when the trajectory of the forelimb changes from swing to stance or stance to swing. During treadmill braking 51% of the cells exhibited complex spike modulation (70/137). A number of different patterns of climbing fiber afferent modulation occurred. The most common pattern was an increase in complex spike discharge with the resumption of the treadmill movement and locomotion. Analysis of the time of these periods of increased climbing fiber activity suggests that, although in some cells the response is coupled to the treadmill onset, in other cells the modulation occurs at longer latencies. Subsequent analysis aligning the EMG, displacement, and treadmill velocity signals with the times of the climbing fiber afferent discharge suggested some responses were coupled to the reinitiation of the locomotor cycle. The second most common pattern was an increase in climbing fiber afferent discharge at the onset of the perturbation. Also, in some cells, complex spike discharge decreased during the period in which the step cycle was arrested.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Intra-axonal recordings of cutaneous primary afferents during fictive locomotion in the cat.

1. Cutaneous primary afferents were recorded intracellularly during fictive locomotion in decorticated cats with the goal of improving our understanding of how locomotor networks might centrally control the transmission in cutaneous pathways at a presynaptic level. 2. Identified cutaneous axons from superficialis peroneal nerve (SP) or tibialis posterior nerve (TP) were recorded intracellularly together with the electroneurograms (ENGs) of representative flexor and extensor muscle nerves of the hindlimb as well as dorsal root potential from L6 or L7 (DRP). Fictive locomotion occurred spontaneously after decortication (n = 12) or was induced by stimulation of the mesencephalic locomotor region (MLR) (n = 6). 3. The results revealed that all cutaneous axons (82 units with resting potential greater than 45 mV) showed fluctuations of their membrane potential (greater than or equal to 0.5 mV) at the rhythm of the fictive locomotion. The characteristics of fluctuation patterns, common to all cutaneous units, consisted of two depolarization waves per cycle: one related to the flexor activity, the other related to the extensor activity. The flexor-related depolarization was followed by a sharp trough of membrane repolarization. The extensor-related depolarization usually overlapped partly with the flexor-depolarization of the following cycle. The relative size of each depolarization could vary among different afferents of the same nerve in the same animal. Hence, maximal depolarization could occur in different parts of the locomotor cycle, but, for the majority of units (82%), it occurred during the flexor activity. These results were similar for SP and TP units. 4. Twenty percent of the units were discharging with a constant or irregular frequency. Phasic antidromic discharges related to locomotor ENGs were rarely encountered (5/82 units). 5. Linear regression analysis of the temporal relationships between fluctuations of membrane potential of cutaneous axons and locomotor bursts over several cycles showed that the timing of presynaptic events in cutaneous afferents is related to the events of the locomotor output. However, the same type of analysis showed that the amplitude of axonal depolarizations and the amplitude of flexor and extensor locomotor bursts could vary independently. Tight temporal relationships were also found between the depolarizations recorded in cutaneous units and the fluctuations recorded at the dorsal root level (DRP). 6. Based on the assumption that the locomotor fluctuations of cutaneous membrane potential are mediated through the primary afferent depolarization (PAD) pathways associated with presynaptic inhibition, it is proposed that the central pattern generator for locomotion (CPG) could phasically control the efficacy of transmission of cutaneous pathways at a presynaptic level as part of the locomotor program.

Animals↗
PubMed1990

Monosynaptic and dorsal root reflexes during locomotion in normal and thalamic cats.

1. In normal and thalamic walking cats electrical stimulation of muscle nerves via chronically implanted electrodes produced electromyographic (EMG) and neurographic responses that were modulated in amplitude depending on the phase of the step cycle. These responses were examined for possible indications of effects of primary afferent depolarization (PAD) during stepping. 2. Monosynaptic reflexes (MSRs) produced by stimulating the lateral gastrocnemius (LG) and medial gastrocnemius (MG) nerves were recorded as EMGs in MG or LG muscles during treadmill locomotion in normal cats. These heteronymous MSR responses were greatest during the stance (extensor) phase. 3. In the same animals, after decerebration, similar modulation of the heteronymous ankle extensor MSRs occurred during spontaneous locomotion with the use of the same stimulus and recording sites. 4. In both normal and thalamic cats the amplitude of neurogram responses recorded from LG or MG nerve after stimulation of the other muscle nerve varied with phase of stepping but did not parallel the variations of the MSR measured as EMG amplitude in the same muscle. The nerve responses were largest during the flexion phase of the step cycle and had a calculated central latency of 0.6-1.0 ms. These are interpreted as arising from antidromic activity in large-caliber afferent nerve fibers (i.e., dorsal root reflexes). 5. Spontaneous antidromic activity in severed L7 dorsal rootlet fibers to triceps surae was observed in the thalamic cats during episodes of locomotion and was closely correlated with flexion phase EMG activity in semitendinosus, a bifunctional muscle. 6. In decerebrate cats, dorsal root reflexes (DRRs) in severed filaments of L4-L7 dorsal roots were produced by stimulation of saphenous and posterior tibial nerves. These DRRs were always smaller during locomotion than during rest and were smallest during the flexion phase. 7. The short-latency antidromic activity produced in muscle nerves by stimulating heteronymous muscle nerves thus appears to be a DRR produced in Group I terminal arborizations that are depolarized close to threshold during the flexion phase. Such PAD could account for changes in the MSR that do not always parallel the levels of recruitment of the motor pools as manifest by background EMG amplitude.

Animals↗
PubMed1993

Activity of medullary reticulospinal neurons during fictive locomotion.

1. The pattern of discharge of medullary reticulospinal neurons, identified by antidromic stimulation applied at the L1-L2 segment of the spinal cord, was studied during fictive locomotion, occurring spontaneously, or evoked by stimulation of the mesencephalic locomotor region in high-decerebrate, paralyzed cats. Unitary recordings were made in the medial reticular formation (P5.0-14.0 mm; L0.5-2.0 mm), and the fictive locomotor pattern was monitored by recording the electroneurogram (ENG) of representative flexor and extensor muscle nerves from each of the four limbs. 2. In total, 117 reticulospinal neurons were recorded in 15 cats. Among these, 73.5% (86/117) modified their discharge at the onset of locomotion. These cells were divided into three subpopulations: 34/86 of the cells always maintained a fixed temporal relationship with the activity of one of the recorded nerves (ENG-related = 39.6%); the pattern of discharge of 42/86 cells was related to the locomotor rhythm [(LR-related-48%)] but was not temporally correlated with any of the recorded nerves; and the remaining 10 cells increased their firing frequency at the onset of locomotion but remained tonic (TONIC-11.6%). 3. Of the ENG-related neurons, 64.8% were temporally correlated to extensor nerve activity, whereas the remaining 35.2% were correlated to flexor nerves. These neurons were either related to forelimb (55.9%) or hindlimb (44.1%) nerves lying either ipsilateral (38.2%) or contralateral (61.8%) to the recording site. A few neurons (n = 3; 8.8%) were related to nerve activity of more than one limb. 4. The pattern of discharge of the LR-related neurons, although not correlated to the activity of any one recorded nerve, could be preferentially related to the locomotor rhythm in either the forelimbs (12/23) or hindlimbs (11/23). 5. ENG- and LR-related reticulospinal neurons were intermingled in the medial reticular formation. In both cases, cells related to the forelimbs were located more dorsally than those related to the hindlimbs. It is suggested that both the ENG- and LR-related neurons represent a single functional population of reticulospinal neurons that is part of an intrinsically organized reticulospinal system that functions to coordinate the activity of the skeletal musculature. 6. The present results show that the majority of reticular neurons projecting as far as the lumbar spinal cord are phasically modulated during locomotion, even in the absence of phasic peripheral afferent inputs. Moreover, the complexity of the discharge patterns in paralyzed animals was found to be similar to that observed in the intact cat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Differential modulation of disynaptic cutaneous inhibition and excitation in ankle flexor motoneurons during fictive locomotion.

1. Intracellular recording from extensor digitorum longus (EDL) and tibialis anterior (TA) alpha-motoneurons during fictive locomotion was used to examine patterns of modulation of oligosynaptic postsynaptic potentials (PSPs) produced by electrical stimulation of the cutaneous superficial peroneal (SP) and medial plantar (MPL) nerves in unanesthetized, decerebrate adult cats. 2. In all 20 EDL motoneurons studied, electrical stimulation of the SP nerve with single pulses at about twice threshold for the most excitable fibers in the nerve (2xT) produced either no synaptic potentials or relatively small oligosynaptic excitatory or inhibitory PSPs (EPSPs or IPSPs), both at rest and during the extension phase of fictive stepping. However, at the onset of the flexion phase large, presumably disynaptic IPSPs (central latencies 1.7-2.0 ms) appeared in the SP responses. These IPSPs usually decreased in amplitude later in the flexion phase despite maintained membrane depolarization. 3. In most (7/8) TA motoneurons, SP stimulation produced oligosynaptic EPSPs at rest and during the extension phase of fictive stepping. These EPSPs were suppressed during flexion in a majority of TA cells studied (5/8) but no clearly disynaptic IPSPs were found in any TA motoneuron. 4. In most EDL and TA motoneurons, stimulation of the MPL nerve produced oligosynaptic EPSPs at rest and during the extension phase, most with latencies in the presumably disynaptic range (< or = 2.0 ms). When present, these MPL EPSPs were suppressed throughout the flexion phase of stepping in almost all EDL (18/ 20) and TA (6/8) motoneurons examined. 5. The available evidence suggests that these modulation effects during fictive stepping are due primarily to convergence of control information from the spinal central pattern generator (CPG) for locomotion onto segmental interneurons in the oligosynaptic cutaneous pathways. 6. These observations extend the evidence for precise differential control of transmission through cutaneous reflex pathways in the cat hindlimb by the locomotor CPG. Taken together with earlier evidence about locomotor modulation of cutaneous PSPs in flexor digitorum longus (FDL) motoneurons, the data suggest that cutaneous information from the dorsal surface of the foot, carried in part by the SP nerve, projects to digit motoneurons (FDL and EDL) through discrete sets of last-order interneurons that also receive powerful excitation from the locomotor CPG during flexion. In contrast, the last-order interneurons that convey excitatory information from the SP nerve to at least some TA motoneurons are inhibited by the CPG during flexion. 7. Another contrast resides in the fact that oligosynaptic cutaneous excitation from the plantar surface of the foot, via the MPL nerve, is suppressed in FDL, EDL, and TA motoneurons during the flexion phase of locomotion. The available information is consistent with the possibility that MPL effects may be delivered to these motor nuclei by common interneurons. 8. We suggest an interneuronal circuitry that could account for these observations and discuss possible functional implications of modulation of these sensory pathways during locomotion.

Animals↗