Biomedical subjects

Arthur Prochazka

Publications and source records attributed to Arthur Prochazka.

9 recordsLinked to original sources

PubMed2007

Intraspinal stimulation caudal to spinal cord transections in rats. Testing the propriospinal hypothesis.

Many laboratories have reported the successful regeneration of neurons across damaged portions of the spinal cord. Associated improvements in hindlimb locomotor movements have been attributed to the formation of functional neuronal connections with the locomotor central pattern generator (CPG). However, regenerating axons generally extend no more than 10 mm caudal to the lesion sites, terminating about 20 mm short of the lumbar segments thought to contain the CPG. It has therefore tacitly been assumed that the locomotor improvements arose from activation of propriospinal neurons relaying excitation to the CPG. Here we report a test of this assumption, which we call the propriospinal hypothesis. Intraspinal microstimulation (ISMS) was used to activate the putative propriospinal relay neurons. Approximately 2-3 wk after complete spinal cord transection at T8-T9 in rats, an array of six Pt-Ir microwires was chronically implanted in the intermediate and ventral gray matter of T10-T12 segments. ISMS pulse trains with amplitudes of 0.8-0.9 times threshold for activating axial muscles were delivered during open-field locomotor tests (BBB). ISMS significantly increased BBB scores over control tests, but did not produce limb coordination and weight bearing sufficient for locomotion. These results support the main assumption of the propriospinal hypothesis: that neuronal activity elicited in thoracic spinal segments caudal to a complete spinal cord transection may propagate caudally and activate the locomotor CPG.

Animals↗

PubMed2006

Control of urinary bladder function with devices: successes and failures.

The management of urinary tract dysfunction is crucial for the health and well-being of people with spinal cord injury. Devices, specifically catheters, play an important role in the daily regime of bladder management for most people with spinal cord injury. However, the high incidence of complications associated with the use of catheters, and the fact that the spinal segments involved in lower urinary tract control remain intact in most cord-injured people, continue to motivate research into devices that could harness the nervous system to provide greater control over lower urinary tract function. Mechanical devices discussed in this review include catheters, artificial urethral sphincters, urethral stents and intraurethral pumps. Additionally, many attempts to restore control of the lower urinary tract with electrical stimulation have been made. Stimulation sites have included: inside the bladder, bladder wall, thigh, pelvic floor, dorsal penile nerve, pelvic nerve, tibial nerve, sacral roots, sacral nerves and spinal cord. Catheters and sacral root stimulators are two techniques whose efficacy is well established. Some approaches have proven less successful and others are still in the development stage. Modifications to sacral root stimulation including posterior root stimulation, anodal blockade and high-frequency blockade as well as new techniques including intraspinal microstimulation, urethral afferent stimulation and injectable microstimulators are also discussed. No single device has yet restored the control and function of the lower urinary tract to the pre-injury state, but new techniques are bringing this possibility closer to reality.

Catheterization↗

PubMed2006

Decoding sensory feedback from firing rates of afferent ensembles recorded in cat dorsal root ganglia in normal locomotion.

Sensory feedback is required by biological motor control systems to maintain stability, respond to perturbations, and adapt. Similarly, motor neuroprostheses require feedback to provide natural and complete restoration of motor functions. In this paper, we show that ensemble firing rates from the body's mechanoreceptors can provide a natural source of kinematic state feedback and could be useful for prosthetic control. Single unit recordings from multiple primary afferent neurons were obtained during walking using multichannel electrode arrays implanted chronically in the L7 dorsal root ganglia of three cats. We typically recorded simultaneously from over 20-30 neurons during the first 7-14 days after surgery, but recordings gradually worsened thereafter. Histology indicates that a ring of inflammatory and connective tissues (100 microm thick) develops around each microelectrode and likely contributes to the degradation in recording quality. Accurate estimates of the hindlimb trajectory were made using a linear filter with inputs from only a few neurons highly correlated with limb kinematics. The coefficients for the linear filter were identified in a least-squares fit with 5-10 s of walking data (model training stage). The estimated and actual trajectories of separate walking data generally match well for walking at a range of speeds accounting for 63 +/- 22% (mean +/- S.D. for hip, knee, and ankle) of the variance in joint angle and 72 +/- 4% of the variance in joint angular velocities. These results indicate that a neural interface with primary sensory neurons in the dorsal root ganglion can provide accurate kinematic state information that may be useful for closed loop control of a neuroprosthesis.

Action Potentials↗

PubMed2004

A functional electric stimulation-assisted exercise therapy system for hemiplegic hand function.

OBJECTIVE: To test a functional electric stimulation (FES)-assisted exercise therapy system for improvement of motor function of the hemiplegic upper extremity. DESIGN: A before-after trial, with 2-month follow-up. SETTING: A university research laboratory. PARTICIPANTS: A convenience sample of 6 subjects (3 men, 3 women). Main inclusion criteria were that stroke had occurred more than 1 year before the study (mean time poststroke, 5.6+/-4.4y) and had resulted in hemiplegia, and that FES produced adequate hand opening. INTERVENTION: A prototype workstation with instrumented objects was used by subjects to perform a set of tasks with their affected hand during 1-hour sessions for 12 consecutive workdays. A FES stimulator was used to assist hand opening. Main outcome measures Kinematic data, provided by the workstation sensors, and 3 clinical tests. RESULTS: Kinematic data indicated statistically significant improvement in subjects' performance (pre-/posttreatment effect size [pre/post ES] of the mean performance scores=5.46; mean pretreatment/follow-up ES [pre/FU ES]=3.44). Two of 3 clinical tests showed improvement in hand function (mean pre/post ES=.51; mean pre/FU ES=.61). CONCLUSIONS: Improvement in hemiplegic hand function because of FES-assisted therapy was documented in a small group of people with hemiplegia whose motor impairment would exclude them from participation in constraint-induced movement therapy. However, the long-term clinical relevance of such improvement needs further study.

Analysis of Variance↗

PubMed2004

Movements elicited by electrical stimulation of muscles, nerves, intermediate spinal cord, and spinal roots in anesthetized and decerebrate cats.

Electrical stimulation offers the possibility of restoring motor function of paralyzed limbs after spinal-cord injury or stroke, but few data are available to compare possible sites of stimulation, such as muscle, nerve, spinal roots, or spinal cord. The aim of this study was to establish some characteristics of stimulation at these sites in the anesthetized and midcollicular decerebrate cat. The hind limb was constrained to move in the sagittal plane against a spring load. Ventral-root stimulation only produced movements down and back; the direction moved systematically backward the more caudal the stimulated roots. In contrast, dorsal-root stimulation only produced movements up and forward. Thus, neither method alone could produce the full range of normal movements. Muscle, nerve, and intraspinal stimulation within the intermediate regions of the gray matter generated discrete, selective movements in a wide range of directions. Muscle stimulation required an order of magnitude more current. Single microwire electrodes located in the spinal gray matter could activate a synergistic group of muscles, and generally had graded recruitment curves, but the direction of movement occasionally changed abruptly as stimulus strength increased. Nerve stimulation produced the largest movements against the spring load (>80% of the passive range of motion) and was the most reproducible from animal to animal. However, recruitment curves with nerve stimulation were quite steep, so fine control of movement might be difficult. The muscle, nerve, and spinal cord all seem to be feasible sites to restore motor function. The pros and cons from this study may be helpful in deciding the best site for a particular application, but further tests are needed in the chronically transected spinal cord to assess the applicability of these results to human patients.

Anesthesia↗

PubMed2002

Sensory control of locomotion: reflexes versus higher-level control.

In the absence of sensory input, the central nervous system can generate a rhythmical pattern of coordinated activation of limb muscles. Contracting muscles have spring-like properties. If synergistic muscles are co-activated in the right way, sustained locomotion can occur. What is the role of sensory input in this scheme? In this chapter we first discuss the implications of positive force feedback control in hindlimb extensor reflexes in the cat. We then raise the question of whether the sensory-evoked responses, which are modest in size and quite delayed in the stance phase, contribute to any significant extent. A locomotor model is used to show that when centrally generated activation levels are low, stretch reflexes can be crucial. However, when these levels are higher, stretch reflexes have a less dramatic role. The more important role for sensory input is probably in mediating higher level control decisions.

Animals↗

PubMed2002

Activation and coordination of spinal motoneuron pools after spinal cord injury.

Goal-directed movements of the limbs involve the coordinated activation of dozens of muscles. The neural signals activating these muscles are organized at spinal and supraspinal levels, the end result being trains of action potentials delivered to muscles by ensembles of spinal motoneurons (MNs). A new modelling approach has allowed us to visualize the activity of MNs controlling cat hindlimb locomotion. This reveals a rostrocaudal oscillation of MN activity distributed over about 30 mm of the lumbosacral spinal cord. The coordination and topographical distribution of MN pools thus revealed put an interesting perspective on the restoration of motor function with regeneration and neuroprosthetic techniques. Recent progress in the area of intraspinal microstimulation (ISMS) is reviewed, including the synthesis of locomotor movements with a small number of implanted microwires, eliciting movements after a spinal transection and facilitating weak voluntary movements with subliminal ISMS. We suggest that neuroprostheses may be useful in maximizing the benefits of neural regeneration in the future.

Animals↗

PubMed2002

Intraspinal micro stimulation generates locomotor-like and feedback-controlled movements.

Intraspinal microstimulation (ISMS) may provide a means for improving motor function in people suffering from spinal cord injuries, head trauma, or stroke. The goal of this study was to determine whether microstimulation of the mammalian spinal cord could generate locomotor-like stepping and feedback-controlled movements of the hindlimbs. Under pentobarbital anesthesia, 24 insulated microwires were implanted in the lumbosacral cord of three adult cats. The cats were placed in a sling leaving all limbs pendent. Bilateral alternating stepping of the hindlimbs was achieved by stimulating through as few as two electrodes in each side of the spinal cord. Typical stride lengths were 23.5 cm, and ample foot clearance was achieved during swing. Mean ground reaction force during stance was 36.4 N, sufficient for load-bearing. Feedback-controlled movements of the cat's foot were achieved by reciprocally modulating the amplitude of stimuli delivered through two intraspinal electrodes generating ankle flexion and extension such that the distance between a sensor on the cat's foot and a free sensor moved back and forth by the investigators was minimized. The foot tracked the displacements of the target sensor through its normal range of motion. Stimulation through electrodes with tips in or near lamina IX elicited movements most suitable for locomotion. In chronically implanted awake cats, stimulation through dorsally located electrodes generated paw shakes and flexion-withdrawals consistent with sensory perception but no weight-bearing extensor movements. These locations would not be suitable for ISMS in incomplete spinal cord injuries. Despite the complexity of the spinal neuronal networks, our results demonstrate that by stimulating through a few intraspinal microwires, near-normal bipedal locomotor-like stepping and feedback-controlled movements could be achieved.

Animals↗

PubMed2002

Spatiotemporal activation of lumbosacral motoneurons in the locomotor step cycle.

The aim of this study was to produce a dynamic model of the spatiotemporal activation of ensembles of alpha motoneurons (MNs) in the cat lumbosacral spinal cord during the locomotor step cycle. The coordinates of MNs of 27 hindlimb muscles of the cat were digitized from transverse sections of spinal cord spanning the entire lumbosacral enlargement from the caudal part of L(4) to the rostral part of S(1) segments. Outlines of the spinal cord gray matter were also digitized. Models of the spinal cord were generated from these digitized data and displayed on a computer screen as three-dimensional (3-D) images. We compiled a chart of electromyographic (EMG) profiles of the same 27 muscles during the cat step cycle from previous studies and used these to modulate the number of active MNs in the 3-D images. The step cycle was divided into 100 equal intervals corresponding to about 7 ms each for gait of moderate speed. For each of these 100 intervals, the level of EMG of each muscle was used to scale the number of dots displayed randomly within the volume of the corresponding MN pool in the digital model. One hundred images of the spinal cord were thereby generated, and these could be played in sequence as a continuous-loop movie representing rhythmical stepping. A rostrocaudal oscillation of activity in hindlimb MN pools emerged. This was confirmed by computing the locus of the center of activation of the MNs in the 100 consecutive frames of the movie. The caudal third of the lumbosacral enlargement showed intense MN activity during the stance phase of locomotion. During the swing phase, the focus of activation shifted abruptly to the rostral part of the enlargement. At the stance-swing transition, a transient focus of activity formed in the most caudal part of the lumbosacral enlargement. This was associated with activation of gracilis, posterior biceps, posterior semimembranosus, and semitendinosus muscles. These muscles move the foot back and up to clear the ground during locomotion, a role that could be described as retraction. The spatiotemporal distribution of neuronal activity in the spinal cord during normal locomotion with descending control and sensory inputs intact has not been visualized before. The model can be used in the future to characterize spatiotemporal activity of spinal MNs in the absence of descending and sensory inputs and to compare these to spatiotemporal patterns in spinal MNs in normal locomotion.

Animals↗