Marc Bélanger

Chapter 18 Modification of reflexes in normal and abnormal movements

The trajectories observed for the limb during human locomotion are determined by a mixture of influences, some arising from neural circuits entirely within the central nervous system and others arising from a variety of sensory receptors. Muscle reflexes are highly modulated during locomotion in an adaptive manner within each phase of the step cycle. Furthermore, the modulation can be modified quickly for different tasks such as standing, walking and running, probably by changes in presynaptic inhibition. This modulation is often lost or severely reduced in patients with spasticity after spinal cord or head injury. In normal subjects cutaneous reflexes can be completely reversed from exciting to inhibiting a muscle during each step cycle, particularly in muscles that normally show two bursts of activity per cycle (e.g., tibialis anterior). In some patients stimulation of a mixed nerve (e.g., common peroneal) can directly produce muscle contraction, generate a reflex response (flexor reflex) and transiently reduce spasticity in antagonist (extensor) muscles. Thus, simple systems employing stimulation can enhance gait to a certain extent in patients with incomplete injuries.

Effects of bilateral Achilles tendon vibration on postural orientation and balance during standing

OBJECTIVE Altering proprioceptive information in the lower limbs by vibration produces direction-specific falling and postural instability, which can persist after vibration stops. The objectives of this study were to describe the changes in trunk and lower limbs postural orientation and muscles activities during and after the end of bilateral Achilles tendon vibration (TV). METHODS Twelve healthy young subjects were exposed to 30s periods of TV while blindfolded. Whole-body kinematics, kinetics and EMG of eight lower limb and trunk muscles were recorded prior, during and 5 or 25s after TV. RESULTS TV during quiet standing produced a whole-body backward shift characterized by greater extension in the trunk and lower limbs. Five seconds after TV, two trends of recovery could be observed, either an overcorrection or undercorrection of the initial position. CONCLUSIONS A continuum of postural orientations are adopted during and after vibration and the movements are not restricted to the ankle joints, despite the local nature of the proprioceptive stimulation. SIGNIFICANCE The widespread influence of vibration as a proprioceptive stimulation when assessing its effects on posture and balance needs to be considered. Further studies should include whole-body analyses to document more thoroughly the postural strategies for balance maintenance during vibration.

Perceived Physiological and Orgasmic Sensations at Ejaculation in Spinal Cord Injured Men

INTRODUCTION With the advances in penile vibrator stimulation (PVS), most spinal cord injured (SCI) men can self-ejaculate. Oral midodrine may further increase ejaculation success, while maintaining autonomy. Since most SCI men attempt ejaculation for sexual rather than reproductive purposes, self-ejaculation should be emphasized and sensations explored. AIMS Explore (i) self-ejaculation success rate in SCI men; (ii) vascular parameters indicative of autonomic dysreflexia (AD) during sexual stimulation and ejaculation; and (iii) sensations associated with ejaculation. METHODS Ejaculation was assessed on 81 SCI men with complete ASIA A (49%) and incomplete B to D lesions (51%), subdivided into tetraplegics (C2-T2), paraplegics sensitive to AD (T3-T6), paraplegics not sensitive to AD (T7-T10), paraplegics with lesions to the emission pathway (T11-L2), and paraplegics with lesions interrupting the emission-ejaculation pathways (L3-below). Natural stimulation was attempted first followed, if negative, by PVS followed, if again negative, by PVS combined with oral midodrine (5-25 mg). MAIN OUTCOME MEASURES Ejaculation success, systolic and diastolic blood pressure, and perceived physiological and orgasmic sensations. RESULTS Overall 91% reached ejaculation, 30% with natural stimulation, 49% with PVS and 12% with midodrine plus PVS. Midodrine salvaged up to 27% depending upon the lesion. Physiological and orgasmic sensations were perceived significantly more at ejaculation than sexual stimulation. Tetraplegics did not differ from paraplegics sensitive to AD on perceived cardiovascular and muscular sensations, but perceived significantly more autonomic sensations, and generally more physiological sensations than lower lesions unsensitive to AD. CONCLUSION Most SCI men can self-ejaculate and perceive physiological and orgasmic sensations. The climactic experience of ejaculation seems related to AD, few sensations being reported when AD is not reached, pleasurable climactic sensations being reported when mild to moderate AD is reached, and unpleasant or painful sensations reported with severe AD. Sexual rehabilitation should emphasize self-ejaculation and self-exploration and consider cognitive reframing to maximize sexual perceptions.

Chapter 3 Electrical stimulation for therapy and mobility after spinal cord injury

This article reviews the use of therapeutic and functional electrical stimulation in subjects after a spinal cord injury (SCI). Muscles become much weaker and more fatigable, while bone density decreases dramatically after SCI. Therapeutic stimulation of paralyzed muscles for about 1 h/day can reverse the atrophic changes and markedly increase muscle strength and endurance as well as bone density. Functional electrical stimulation can also improve the speed and efficiency of walking in people with an incomplete SCI. Finally, a modified wheelchair is described in which electrical stimulation or residual voluntary activation of leg muscles can produce movements of a footrest that is coupled to the wheels. The wheelchair can provide greater mobility and fitness to persons who are not functional walkers and currently use their arms to propel a wheelchair.

Corrective responses to perturbation applied during walking in humans

Modulation of the flexor reflex response during walking in humans following stimulation at 5 points in the step cycle was studied. At heel strike, an extensor response was observed at the ankle and the knee which would allow one to stabilize and plant the ipsilateral foot fast. Later on in the stance, there was a dorsiflexor and an extensor response at the ankle and the knee, respectively, which would result in the removal of the foot from the stimulus without collapsing at the knee. During mid-swing, a flexor reflex response was observed at the ankle and the hip joint. There was a tendency for the normal stride to be longer than the perturbed stride in mid swing and early stance while it was of shorter duration in late stance and early swing.

Effects of plantar cutaneo-muscular and tendon vibration on posture and balance during quiet and perturbed stance.

Modulation of lower limb somatosensory information by tendon or plantar vibration produces directionally specific, vibration-induced falling reactions that depend on the tendon or the region of the sole that is vibrated. This study characterized the effects of different patterns of plantar cutaneo-muscular vibration and bilateral Achilles tendon vibration (ATV) on the postural strategies observed during quiet and perturbed stance. Twelve healthy young participants stood barefooted, with their vision blocked, on two sets of plantar vibrators placed on two AMTI force plates embedded in a moveable support surface. Two other vibrators were positioned over the Achilles tendons. Participants were randomly exposed to different patterns of plantar cutaneo-muscular and ATV. Tilts of the support surface in the toes-up (TU) and toes-down (TD) directions were given 5-8s after the beginning of vibration. Body kinematics in 3D and ground reaction forces were recorded. Bilateral ATV applied with or without rearfoot vibration (RFV) during quiet stance resulted in a whole-body backward leaning accompanied by an increase in trunk extension and hip and knee flexion. RFV alone produced a forward whole-body tilt with increased flexion in trunk, hip, and ankle. When stance was perturbed by TU tilts, the center of mass (CoM) and center of pressure (CoP) displacements were larger in the presence of RFV or ATV and associated with increased peak trunk flexion. TD tilts with or without ATV resulted in no significant difference in CoM and CoP displacements, while larger trunk extension and smaller distal angular displacements were observed during ATV. RFV altered the magnitude of the balance reactions, as observed by an increase in CoP displacements and variable response in trunk displacement. Significant interactions between ATV and RFV were obtained for the peak angular excursions for both directions of perturbations, where ATV either enhanced (for TU tilts) or attenuated (for TD tilts) the influence of RFV. Manipulating somatosensory information from the plantar cutaneo-muscular and muscle spindle Ia afferents thus results in altered and widespread postural responses, as shown by profound changes in body kinematics and CoM and CoP displacements. This suggests that the CNS uses plantar cutaneo-muscular and ankle spindle afferent inputs to build an appropriate reference of verticality that influences the control of equilibrium during quiet and perturbed stance.

Pain Effect on Monosynaptic and Polysynaptic Reflex Inhibition

OBJECTIVE Determine the electrophysiological effects of anterior knee pain using monosynaptic and polysynaptic reflexes. DESIGN A pretest/posttest control group experimental design with repeated measures. SETTING All tests were performed in a university laboratory. PARTICIPANTS Six subjects suffering from patello-femoral dysfunction (PFD) composed the experimental group. These patients were diagnosed and referred by medical and chiropractic doctors. Six healthy subjects were recruited for the control group. INTERVENTION Pain relief by cold application (10 minutes) on the knee. MAIN OUTCOME MEASURES Monosynaptic reflex: H reflex of the superficial portions of the quadriceps femoris. Polysynaptic reflexes: nociceptive flexion response (NFR) of the long head of the biceps femoris. RESULTS Cold application, producing significant pain relief (p < 0.05), did not change H-reflex amplitude (p > 0.05) for both groups and did not show modulation of the NFR. However, the PFD group showed significantly lower pain (p < 0.05) and NFR thresholds (p < 0.05) than the control group. Finally, nociceptive stimulation was applied at the sural nerve during an isometric extension of the knee (20% of maximum electromyographic contraction). After this stimulation, uni-articular extensors, especially the distal fibers of the vastus medialis, showed a longer and stronger inhibition than the bi-articular rectus femoris. CONCLUSIONS Pain episodes do not appear to affect monosynaptic responses. NFR threshold differences found between PFD and control group could be explained by the increased excitability of the nervous system in subjects experimenting painful bouts. Functional implications of these findings are discussed.

Phase-dependent compensatory responses to perturbation applied during walking in humans.

The interaction between the peripheral and the central regulation of locomotion was studied by examining the dependency of the response to unexpected perturbation on the phase of the step cycle. The changes in the latency and magnitude of various muscle responses to electrical stimulation of the toe and applied unexpectedly at different phases of the locomotor cycle in humans are described. The results show that response to perturbation is gated and modulated in both ipsi- and contralateral limb muscles. These muscle responses, when present, were always excitatory in nature. They were not correlated with the normal locomotor activity, thus suggesting a more complex organization of the response. Except for one muscle in the contralateral limb, the latency of the other muscle responses did not vary across the step cycle. in response to the perturbation, the appropriate phase of the step cycle was shortened. The results from this study suggest that the perturbation applied elicits a phase-independent, normal ipsilateral flexor response in the tibialis anterior muscle, while the gating and modulation of other ipsi- and contralateral muscles provide appropriate phase-dependent adaptive response to maintain postural stability and continue with the ongoing task of locomotion.

Blood pressure changes during sexual stimulation, ejaculation and midodrine treatment in men with spinal cord injury

Associate Editor

The Spinal Cat

A number of reviews have summarized important insights on the role played by various nervous system structures in the control of locomotion (1–8). These reviews have also highlighted the remarkable locomotor capacities of the spinal cord after a complete spinal transection, which removes all the ascending and descending pathways normally exerting important control over spinal cord functions. The purpose of this chapter is to focus specifically on the locomotor capabilities of the spinal cat, not so much to show that “spinal” locomotion resembles “normal” locomotion but rather to illustrate the extent to which the spinal cord can express and adapt its locomotor functions in the absence of these regulatory mechanisms. Does this spinal behavior represent the contribution of the spinal cord to normal locomotion? Probably not, because in all pathologic conditions, the central nervous system utilizes whatever circuitry is available to optimize its functions. It is possible that some mechanisms are less important in the normal cat but become essential for locomotion after spinalization, such as some sensory afferents. Thus, a better understanding of the “physiopathology” of locomotion after spinal cord injury in animal models is important both in highlighting some of the principles that may help understand normal locomotion and in increasing our understanding of some of the mechanisms of recovery of a motor function following a spinal trauma. Such knowledge is important for improving the design of various types of therapeutic approaches in spinal-cord-injured patients (9,10).