Biomedical subjects

D F Collins

Publications and source records attributed to D F Collins.

At least 19 recordsLinked to original sources

PubMed2005

Cutaneous receptors contribute to kinesthesia at the index finger, elbow, and knee.

The neural mechanisms underlying the sense of joint position and movement remain controversial. While cutaneous receptors are known to contribute to kinesthesia for the fingers, the present experiments test the hypothesis that they contribute at other major joints. Illusory movements were evoked at the interphalangeal (IP) joints of the index finger, the elbow, and the knee by stimulation of populations of cutaneous and muscle spindle receptors, both separately and together. Subjects matched perceived movements with voluntary movements of homologous joints on the contralateral side. Cutaneous receptors were activated by stretch of the skin (using 2 intensities of stretch) and vibration activated muscle spindle receptors. Stimuli were designed to activate receptors that discharge during joint flexion. For the index finger, vibration was applied over the extensor tendons on the dorsum of the hand, to evoke illusory metacarpophalangeal (MCP) joint flexion, and skin stretch was delivered around the IP joints. The strong skin stretch evoked the illusion of flexion of the proximal IP joint in 6/8 subjects (12 +/- 5 degrees, mean +/- SE). For the group, strong skin stretch delivered during vibration increased the perceived flexion of the proximal IP joint by eight times with a concomitant decrease in perceived flexion of the MCP joint compared with vibration alone (P < 0.05). For the elbow, vibration was applied over the distal tendon of triceps brachii and skin stretch over the dorsal forearm. When delivered alone, strong skin stretch evoked illusory elbow flexion in 5/10 subjects (9 +/- 4 degrees). Simultaneous strong skin stretch and vibration increased the illusory elbow flexion for the group by 1.5 times compared with vibration (P < 0.05). For the knee, vibration was applied over the patellar tendon and skin stretch over the thigh. Skin stretch alone evoked illusory knee flexion in 3/10 subjects (8 +/- 4 degrees) and when delivered during vibration, perceived knee flexion increased for the group by 1.4 times compared with vibration (P < 0.05). Hence inputs from cutaneous receptors, muscle receptors, and combined inputs from both receptors likely subserve kinesthesia at joints throughout the body.

Adult↗

PubMed2004

Forces consistent with plateau-like behaviour of spinal neurons evoked in patients with spinal cord injuries.

Percutaneous electrical stimulation over tibialis anterior and triceps surae was performed in 14 patients with traumatic spinal cord injury (SCI) to look for evidence that 'extra contractions' can develop, beyond those due to activation of the motor axons beneath the stimulating electrodes. Criteria for the extra contractions included marked asymmetry of force with respect to stimulation, progressively rising force during stimulation of constant amplitude and frequency, and force remaining high after stimulation frequency had returned to the control level following a high-frequency burst. Twelve of the 14 patients showed evidence of such behaviour, more frequently in triceps surae than tibialis anterior. Force or electromyographic activity commonly outlasted the stimulation in these patients. There was no apparent correlation between the completeness or level of injury and the ability to induce the behaviour. Evidence of force potentiation and 'habituation' was also seen. Eleven of the 14 patients exhibited hyper-reflexia and reported spontaneous spasms, but there was no obvious association with the extra contractions. It is concluded that non-classical behaviour of neurons within the spinal cord can contribute to the extra contractions evoked by electrical stimulation over muscles in spinal cord-injured subjects. This central contribution is less easy to obtain than in intact healthy subjects, all of whom showed the phenomenon. These contractions are consistent with the activation of plateau potentials in spinal neurons and, if so, plateau potentials may contribute to a patient's clinical manifestations.

Adolescent↗

PubMed2003

The detection of human finger movement is not facilitated by input from receptors in adjacent digits.

These experiments were designed to determine whether cutaneous input from a digit provides a general facilitation of the detection of movements applied to an adjacent digit. The ability to detect passive movements at the proximal interphalangeal joint of the right index finger was measured when cutaneous (and joint) input was removed (using local anaesthesia) from the tip of one or both digits adjacent to the test finger (16 subjects). The same parameter was also measured when input was artificially increased by stimulation of the adjacent digits at three intensities: below, above and at perceptual threshold (PT; 15 subjects). Detection of flexion or extension movements was not altered by anaesthesia of one or both adjacent digits. Since it was possible that too few tonically active afferents in the hand had been blocked to reveal an effect, the median nerve was blocked, with movements applied to the little finger, causing no measurable impairment in acuity (three subjects). Simultaneous electrical stimulation of the tips of the adjacent digits at intensities above PT impaired movement detection, but had no effect when delivered at or below PT. To test whether the effect of detectable electrical stimuli was due to a specific interaction between the artificial input and the input evoked by moving the digit, or due to mental distraction, stimuli were delivered above PT to either the left or right little finger, or the test index finger during movement of the index finger. Electrical stimulation of the index finger significantly reduced detection by approximately 50%, but stimulation of the remote little fingers did not. Electrical stimulation is a non-natural stimulus, so a "natural" stimulus was applied by continuously stroking the tips of the adjacent digits with a brush (10 subjects). The natural stimulus also significantly reduced movement detection by approximately 50%. Together, these findings suggest that tonic inputs from digital nerve afferents adjacent to, or more remote from the passively moved finger do not facilitate movement detection. However, the reduced detection during stimulation of the adjacent digits shows that there is nevertheless some interaction between the various proprioceptive inputs from the digits.

Adult↗

PubMed2002

Sustained contractions produced by plateau-like behaviour in human motoneurones.

Electrical stimulation over human muscle can generate force directly by activation of motor axons and indirectly by 'reflex' recruitment of spinal motoneurones. These experiments were designed to define the properties of the centrally generated 'reflex' force, including the optimal stimulus conditions for producing it in tibialis anterior (TA) and triceps surae (TS), and its interaction with volition. Subjects (n = 21) were seated with their foot strapped to an isometric myograph. Surface EMG was recorded from TS and TA. High-frequency electrical stimulation (100 Hz) of TS and TA with wide pulse widths (1 ms) was most effective to evoke the sustained centrally generated forces. The maximal force evoked by this mechanism during stimulation of TA for 40 s was approximately 42 % of that produced by a maximal voluntary contraction. For both muscle groups, ramp increases and decreases in stimulus frequency (from approximately 4 to 100 Hz and back to 4 Hz over 6 s) resulted in marked hysteresis in the force-frequency plot. After a single 'burst' of 100 Hz stimulation during prolonged stimulation at 25 Hz, force remained elevated. Repeated bursts often generated progressively larger force increments. These behaviours were abolished by an anaesthetic nerve block proximal to the stimulation site, confirming the central origin for the 'extra' force. After a brief voluntary contraction was performed during 25 Hz stimulation, force remained elevated, and this showed some gradation with voluntary contraction amplitude. Sometimes voluntary contractions alone initiated the sustained central motor output. Involuntary contractions often persisted for many seconds after electrical stimulation ceased. These were not terminated by brief inhibitory inputs to the active motoneurones but could be stopped by the voluntary command to 'relax completely'. Overall, these centrally generated contractions are consistent with activation of plateau potentials in motoneurones innervating the ankle dorsiflexors and plantarflexors. Large forces can be produced through this mechanism. The interaction with volitional drives suggests that plateau behaviour may contribute significantly to the normal output of human motoneurones.

Adult↗

PubMed2001

Large involuntary forces consistent with plateau-like behavior of human motoneurons.

When electrical stimulation is applied over human muscle, the evoked force is generally considered to be of peripheral origin. However, in relaxed humans, stimulation (1 msec pulses, 100 Hz) over the muscles that plantarflex the ankle produced more than five times more force than could be accounted for by peripheral properties. This additional force was superimposed on the direct response to motor axon stimulation, produced up to 40% of the force generated during a maximal voluntary contraction, and was abolished during anesthesia of the tibial nerve proximal to the stimulation site. It therefore must have resulted from the activation of motoneurons within the spinal cord. The additional force could be initiated by stimulation of low-threshold afferents, distorted the classical relationship between force and stimulus frequency, and often outlasted the stimulation. The mean firing rate of 27 soleus motor units recorded during the sustained involuntary activity after the stimulation was 5.8 +/- 0.2 Hz. The additional force increments were not attributable to voluntary intervention because they were present in three sleeping subjects and in two subjects with lesions of the thoracic spinal cord. The phenomenon is consistent with activation of plateau potentials within motoneurons and, if so, the present findings imply that plateau potentials can make a large contribution to forces produced by the human nervous system.

Adult↗

PubMed2001

Human interlimb reflexes evoked by electrical stimulation of cutaneous nerves innervating the hand and foot.

There is some discrepancy over the extent to which reflex pathways from different cutaneous nerves in the hand and foot link the cervical and lumbar spinal cord in neurologically intact humans. The present experiments were designed to determine whether stimulation of a cutaneous nerve in the foot or in the hand evoked reflexes in the non-stimulated limbs (interlimb reflexes). Reflexes were elicited by stimulating (5x1-ms pulses at 300 Hz) the superficial peroneal (SP; innervates the foot dorsum) or superficial radial (SR; innervates the dorsolateral portion of the hand) nerve while subjects (n=10) performed focused contractions of different upper and lower limb muscles. Reflex responses were divided into early (<75 ms), middle (75-120 ms), and late (>120 ms) epochs as determined from averages of 50 sweeps of stimulus-locked electromyographic activity. Significant interlimb reflexes were found at the early latency in 44/106 and 44/103 muscles sampled after SP and SR nerve stimulation, respectively. At the middle latency, significant interlimb reflexes were seen in 89/106 and 87/103 muscles sampled after SP and SR nerve stimulation, respectively. Interlimb reflexes were seen when stimulating at the wrist (i.e. SR nerve) and when stimulating at the ankle (i.e. SP nerve) with an equal probability. The results show that interlimb cutaneous reflexes are widely distributed in humans. The mean latency of the earliest response was quite short and may be mediated by a propriospinal pathway. Functionally, these pathways may provide a substrate for transferring information to coordinate movements between the limb segments.

Action Potentials↗

PubMed2000

Sensory integration in the perception of movements at the human metacarpophalangeal joint.

These experiments were designed to investigate illusions of movements of the fingers produced by combined feedback from muscle spindle receptors and receptors located in different regions of the skin of the hand. Vibration (100 Hz) applied in cyclic bursts (4 s 'on', 4 s 'off') over the tendons of the finger extensors of the right wrist produced illusions of flexion-extension of the fingers. Cutaneous receptors were activated by local skin stretch and electrical stimulation. Illusory movements at the metacarpophalangeal (MCP) joints were measured from voluntary matching movements made with the left hand. Localised stretch of the dorsal skin over specific MCP joints altered vibration-induced illusions in 8/10 subjects. For the group, this combined stimulation produced movement illusions at MCP joints under, adjacent to, and two joints away from the stretched region of skin that were 176 +/- 33, 122 +/- 9 and 67 +/- 11 % of the size of those from vibration alone, respectively. Innocuous electrical stimulation over the same skin regions, but not at the digit tips, also 'focused' the sensation of movement to the stimulated digit. Stretch of the dorsal skin and compression of the ventral skin around one MCP joint altered the vibration-induced illusions in all subjects. The illusions became more focused, being 295 +/- 57, 116 +/- 18 and 65 +/- 7 % of the corresponding vibration-induced illusions at MCP joints that were under, adjacent to, and two joints away from the stimulated regions of skin, respectively. These results show that feedback from cutaneous and muscle spindle receptors is continuously integrated for the perception of finger movements. The contribution from the skin was not simply a general facilitation of sensations produced by muscle receptors but, when the appropriate regions of skin were stimulated, movement illusions were focused to the joint under the stimulated skin. One role for cutaneous feedback from the hand may be to help identify which finger joint is moving.

Electric Stimulation↗

PubMed2000

Spinal cord microstimulation generates functional limb movements in chronically implanted cats.

Spinal cord injuries disrupt the communication between the brain and peripheral nerves, but leave motoneurons and networks of interneurons below the level of the lesion intact. It is therefore possible to restore some function following injury by providing an artificial stimulus to the surviving neurons below the level of the lesion. We report here on a novel approach for generating functional movements by electrically stimulating the spinal cord through chronically implanted ultrafine, hair-like electrodes. Six to 12 microwires were implanted in the lumbar enlargement of intact cats for 6 months. Twice a week, trains of stimuli were delivered through each microwire and the evoked electromyographic and torque responses were recorded. Strong coordinated hindlimb movements were obtained by stimulating through individual electrodes. The joint torques elicited were capable of supporting the animals' hindquarters. The responses were stable over time and the contractions caused no apparent discomfort to the animals. No obvious motor deficits were seen throughout the 6-month duration of implantation. The results demonstrate that microwires implanted in the spinal cord remain stably in place and stimulation through these electrodes produces strong, controllable movements. This provides a promising basis for the use of spinal cord neuroprostheses in restoring mobility following spinal cord injury.

Animals↗

PubMed1999

Contact-evoked changes in EMG activity during human grasp.

Contact-evoked changes in EMG activity during human grasp. 2215 Cutaneous receptors in the digits discharge bursts of activity on contact with an object during human grasp. In this study, we investigated the contribution of this sensory activity to the responses of muscles involved in the task. Twelve subjects performed a standardized precision grasp task without the aid of vision. Electromyographic (EMG) responses in trials when the object was present were compared with those in which the object, and hence the associated afferent responses, were unexpectedly absent. Significant differences in EMG amplitude occurred in the interval 50-100 ms after contact in all subjects and in 33/46 of the muscles sampled. The differences emerged as early as 34 ms after contact and comprised as much as a fourfold change in EMG from 50 to 100 ms after contact with the object. Typically, EMG responses were larger when the object was present (OP), though there were cases, particularly in the thenar muscles, in which the responses increased when the object was absent (OA). Local anesthesia of the thumb and index finger attenuated contact-evoked EMG activity in at least one muscle in all four subjects tested. In one subject, contact-evoked responses were abolished completely during the anesthesia in all four muscles sampled. The results indicate that the sensory activity signaling contact plays a key role in regulating EMG activity during human grasp. Much of this feedback action is attributable to cutaneous receptors in the digits and probably involves both spinal and supraspinal pathways.

Adult↗

PubMed1998

Muscular sense is attenuated when humans move.

1. Muscle receptors play an important role in our conscious perception of movement, but there are no published accounts of our ability to detect their signals during different motor tasks. The present experiments introduce a method to test muscular sense when humans move. 2. Muscle receptors were excited by an electrically induced twitch of the right extensor carpi ulnaris muscle. The muscle was stimulated via percutaneously inserted intramuscular electrodes or using surface stimulation through anaesthetized skin. Muscular sense was represented by the ability to detect the twitch and was compared between various tasks and stationary control trials. 3. Three hertz voluntary wrist movements significantly attenuated muscular sense to 37 % of control. This velocity-dependent attenuation was present over a range of twitch amplitudes suggesting it does not simply reflect a masking of low intensity stimuli. Perceptual ratings of twitch amplitude during fast imposed passive movements were reduced by 40 %, though this did not quite reach statistical significance. However, perceptual ratings of twitches evoked up to 2 s after the termination of the passive movements were significantly different from control. 4. Reaching with the stimulated, but not the contralateral, arm also significantly reduced muscular sense (to 40 %). 5. Attenuation to 58 % of control during cyclic stretching of the skin on the dorsum of the hand showed that signals from peripheral receptors may play a role. Attenuation prior to a single wrist flexion movement indicated that central sources can also contribute. 6. The results are consistent with current findings of a general attenuation of sensory feedback during movement and raise questions regarding the role of muscular sense in movement control.

Adult↗

PubMed1997

Sensori-sensory afferent conditioning with leg movement: gain control in spinal reflex and ascending paths.

Studies are reviewed, predominantly involving healthy humans, on gain changes in spinal reflexes and supraspinal ascending paths during passive and active leg movement. The passive movement research shows that the pathways of H reflexes of the leg and foot are down-regulated as a consequence of movement-elicited discharge from somatosensory receptors, likely muscle spindle primary endings, both ipsi- and contralaterally. Discharge from the conditioning receptors in extensor muscles of the knee and hip appears to lead to presynaptic inhibition evoked over a spinal path, and to long-lasting attenuation when movement stops. The ipsilateral modulation is similar in phase to that seen with active movement. The contralateral conditioning does not phase modulate with passive movement and modulates to the phase of active ipsilateral movement. There are also centrifugal effects onto these pathways during movement. The pathways of the cutaneous reflexes of the human leg also are gain-modulated during active movement. The review summarizes the effects across muscles, across nociceptive and non-nociceptive stimuli and over time elapsed after the stimulus. Some of the gain changes in such reflexes have been associated with central pattern generators. However, the centripetal effect of movement-induced proprioceptive drive awaits exploration in these pathways. Scalp-recorded evoked potentials from rapidly conducting pathways that ascend to the human somatosensory cortex from stimulation sites in the leg also are gain-attenuated in relation to passive movement-elicited discharge of the extensor muscle spindle primary endings. Centrifugal influences due to a requirement for accurate active movement can partially lift the attenuation on the ascending path, both during and before movement. We suggest that a significant role for muscle spindle discharge is to control the gain in Ia pathways from the legs, consequent or prior to their movement. This control can reduce the strength of synaptic input onto target neurons from these kinesthetic receptors, which are powerfully activated by the movement, perhaps to retain the opportunity for target neuron modulation from other control sources.

Animals↗

PubMed1996

Movement illusions evoked by ensemble cutaneous input from the dorsum of the human hand.

1. In this study we tested the hypothesis that ensemble activity in human cutaneous sensory afferents evoked by the stretching of skin over and around the finger joints contributes to the conscious perception of movement of the fingers. 2. In nineteen normal adults, ensembles of cutaneous afferents were activated either by electrical stimulation, delivered through an array of electrodes on the dorsum of the hand and fingers, or by mechanical stretching of the skin over and around the joints. The stretching was applied through an array of threads stuck to the skin, in such a way as to avoid or minimize moving the underlying joints and to avoid applying pressure to underlying tendons and ligaments. Perceived movements were mimicked by voluntary movements of the fingers of the contralateral hand. 3. By way of comparison, kinaesthetic illusions were also evoked by activation of muscle receptors by vibration. 4. Illusions of movement were elicited with each type of stimulus. Electrical stimulation of skin afferents caused clear illusory movements in six out of seventeen subjects (35%), and borderline movement illusions in three out of the same seventeen subjects (total 9/17, 53%). Various other localized skin sensations were also reported. Skin stretch evoked movement illusions in eleven out of nineteen of subjects (58%). In all subjects who received both cutaneous stimuli, twelve out of seventeen (71%) reported some movement sensations with one or other of the stimulation techniques. Vibration tended to be the most reliable stimulus modality, eliciting illusory movements in fourteen out of sixteen subjects (88%). 5. Although the skin stretching technique did cause minute movements of nearby joints in several cases, these were monitored and shown in separate control experiments to be below perceptual threshold, and so the movement illusions could be safely attributed to the cutaneous afferent input evoked by skin stretch. 6. The results support the hypothesis that input from skin stretched during finger movement contributes to the conscious perception of the movement. Vibration-evoked muscle afferent input tended to be more reliable than the skin input in producing kinaesthetic illusions, though comparisons of the relative efficacy of the three techniques must be made with caution.

Adolescent↗

PubMed1995

Mechanisms within the human spinal cord suppress fast reflexes to control the movement of the legs.

Passive locomotor-like movement induces depression of the gain of a fast conducting spinal sensorimotor path in humans. It was hypothesized that this gain control is mediated through a spinal circuit. In the first experiment, passive pedalling motion was rapidly initiated in eight able bodied subjects. Soleus H-reflexes (used to reveal the gain of the short latency stretch reflex) were recorded over the first 250 ms after the movement started. Significant depression in H-reflex magnitude was observed by 50 ms after the onset of movement. On the basis of the timing, this gain attenuation was likely mediated through a spinal circuit. In a second experiment we tested chronic quadriplegics with clinically complete lesions of the spinal cord. Of five subjects tested, three expressed the reflex and all three showed significant inhibition with passive pedalling movement (mean depression was to 39% of controls). Both the rapid onset of the gain change (Expt. 1) and the presence of movement-induced inhibition in individuals with spinal lesions (Expt. 2) provide evidence that this component of human locomotor control is located in the spinal cord. The initiating source is probably somatosensory receptor discharge due to the movement.

H-Reflex↗

PubMed1993

Contralateral inhibition of soleus H reflexes with different velocities of passive movement of the opposite leg.

The research question was, do events arising from rhythmic passive movement of the human leg lead to inhibition of the H reflex pathway in the stationary leg contralateral to that movement? Further, as the angular velocity of the passive movement increases, does the contralateral reflex inhibition also increase? Stable stimulation of the tibial nerve elicited H reflexes in the EMG of soleus. Trials involved the stimulated or the contralateral leg being rotated passively in a pedalling motion, at various velocities. The controls were made with the subjects seated and relaxed. The results showed that reflex magnitudes were significantly depressed when the test limb was passively rotated at 60 rpm. in comparison to the seated control trials. Rotation of the opposite limb depressed reflex magnitudes in the test limb, which was stationary. This contralateral inhibition increased, (mean reflex magnitudes of 62.68%, 41.04%, 16.65% and 9.58% of peak-to-peak Mmax), as the velocity of rotation of the opposite limb increased (10, 30, 60, 90 rpm, respectively) (P < 0.01). The effect of movement velocity was interpreted as the result of altered sensory receptor discharge arising from the passive movement. It is concluded that contralateral sensory activity contributes to the movement-elicited afferent discharge which tunes the spinal somatosensory-motor mechanisms for human locomotion.

Adult↗

PubMed1993

The independence of premovement H reflex gain and kinesthetic requirements for task performance.

The gain of the H reflex pathway is extensively altered prior to a voluntary contraction. We hypothesized that this gain change is modulated for the kinesthetic requirements of the ensuing task. The experiment involved a simple reaction time task, in which soleus H reflexes were evoked during the final 100 msec before the electromyographic activity for simple ankle movements of low, medium and high requirement for accurate positioning of the foot. The latter two conditions involved tracking and perturbed tracking, respectively. Subjects were required to respond with a non-ballistic movement. Over the 6 subjects and tasks, before plantar flexion, mean reflex magnitudes significantly increased (P < 0.05; to 160% of control, S.D. 60%). Before dorsiflexion they decreased (to 87% of control, S.D. 10%). However, the two accuracy requirements did not significantly alter the soleus H reflex changes, before either plantar flexion or dorsiflexion (P > 0.05). We conclude that the premovement gating of the spinal route from Ia afferents to the autogenic soleus muscle is independent of the changes in the presently tested types of kinesthetic requirements for movement.

Adult↗

PubMed1993

Reversal of the influence of group Ib afferents from plantaris on activity in medial gastrocnemius muscle during locomotor activity.

1. Rhythmic locomotor activity was evoked in clonidine-treated acute and chronic spinal cats, and the effect of stimulating group I afferents from the plantaris muscle on the timing and magnitude of bursts in medial gastrocnemius (MG) motoneurons was examined. 2. The locomotor rhythm was entrained when group I afferents in the plantaris nerve were electrically stimulated with trains of stimuli presented at rates above and below the intrinsic frequency of the rhythmic activity. During entrainment at rates higher than the intrinsic frequency, a burst of activity in ipsilateral MG motoneurons was initiated approximately 40 ms after the onset of each stimulus train. At lower rates of entrainment the onset of MG bursts preceded the onset of the stimulus trains, and each stimulus train had an excitatory effect on the MG burst with a latency in the range of 30-50 ms. A similar excitatory effect was observed when the stimulus trains were triggered at a preset delay after the endogenous generation of the MG bursts. 3. The excitatory action of plantaris group I afferents on the MG motoneurons was only seen during periods of locomotor activity. In the absence of rhythmic activity, the same stimulus trains reduced any ongoing tonic activity in MG motoneurons. 4. Vibration of the plantaris muscle to preferentially activate group Ia afferents neither entrained the locomotor rhythm nor increased the magnitude of the MG bursts. 5. We conclude that during locomotor activity, input from group Ib afferents of the plantaris muscle has an excitatory action on the system of interneurons generating the extensor bursts, i.e., on the extensor half-center of the central rhythm generator.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1992

Movement features and H-reflex modulation. I. Pedalling versus matched controls.

Modulation of soleus H-reflex magnitude over a cycle of leg movement and the adjustment of controls to account for it were explored. During pedalling, H-reflex magnitudes in all nine subjects were highest in the power producing phase and lowest in recovery. Stimulation intensity was standardized. Compared to sitting, these reflexes were significantly depressed (P less than 0.05). The sitting condition was modified in one experiment, so that the angles of the limb joints and the contraction level of soleus were matched to their values, measured at 13 equi-spaced points, around the pedal cycle. This matching resulted in some modulation of the H-reflex around the pedal cycle, when sitting. When the contraction of tibialis anterior was added to these changes to the seated control, this modulation came closer to that seen during movement. Movement-specific modulation of the reflex was now harder to identify. These data raise the question of whether the three features presently used for matching are causative in the movement modulation of the soleus H-reflex and whether they represent effects arising from centrally descending or peripheral sources.

Adult↗

PubMed1992

Movement features and H-reflex modulation. II. Passive rotation, movement velocity and single leg movement.

Modulation of soleus H-reflex magnitudes during pedalling, and their approximation when seated with appropriate joint positions and contractile activity was demonstrated in the previous paper. The present study investigated the modulation of H-reflexes during (A) pedalling movement in the absence of contractile activity, (B) different movement velocities and (C) movement of a single limb. Using a customized tandem cycle ergometer, seated subjects with trunk supported relaxed their leg muscles and allowed their legs to be rotated. Their feet were supported on the pedals with the ankle braced. Reflexes were collected at four phases in the movement cycle (with some at 13 phases) and with speeds of 5-60 revolutions per min (cycle times from 12 to 1 s). The results showed that (i) reflex magnitude substantially decreased with limb rotation (P less than 0.05). The degree of inhibition was dependent on the phase position. (ii) Increasing speed of passive rotation increased the inhibition at all positions, but was most pronounced near the fullest flexion of hip and knee. When subjects actively pedalled, the relationship between speed and inhibition remained. (iii) When the contralateral leg was moved and the target leg was stationary, crossed projection of reflex inhibition was clear. (iv) The reflex gain measured during active pedalling of one leg was similar to that observed during two legged pedalling. Again, a crossed effect from the contralateral leg could be observed. We conclude that the net influence of discharge from movement-elicited afference is inhibitory on this reflex path and that the reflex modulation during pedalling arises from overlaid sources.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗