Biomedical subjects

J Duysens

Publications and source records attributed to J Duysens.

At least 19 recordsLinked to original sources

PubMed2003

Reflex responses in the lower leg following landing impact on an inverting and non-inverting platform.

In the lower leg, landing after a jump induces reflexes, the role of which is not well understood. This is even more so for reflexes following landing on inverting surfaces. The latter condition is of special interest since ankle inversion traumata are one of the most common injuries during sport. Most studies have investigated ankle inversions during a static standing condition. However, ankle injuries occur during more dynamic activities such as jumping. Therefore, the present study aimed at reproducing these situations but in a completely safe setting. EMG responses were recorded after landing on an inverting surface, which caused a mild ankle inversion of 25 deg of rotation (in a range sufficient to elicit reflexes but safe enough to exclude sprains). The results are compared with data from landing on a non-inverting surface to understand the effect of the inversion. In general, landing on the platform resulted in short and long latency responses (SLR and LLR) in triceps surae (soleus, gastrocnemius medialis and lateralis) and peroneal muscles (long and short peroneal) but not in the tibialis anterior muscle. Landing on the inverting platform caused significant LLRs in the peroneal muscles (which underwent the largest stretch) but not in the triceps muscles. Conversely, landing on a non-inverting platform induced larger SLRs in triceps than in the peroneal muscles. Although the peroneal LLRs thus appeared to be selectively recruited in an inverting perturbation, their role during such perturbations should be limited since the latency of these responses was about 90 ms while the inversion lasts only 42 ms. The SLRs, if present, had an onset latency of around 44 ms. In the period following the inversion, however, the responses may be important in preventing further stretch of these muscles.

Adult↗

PubMed2003

Suppressive musculocutaneous reflexes in tibialis anterior following upper leg stimulation at the end of the swing phase.

In the cat it is known that the distribution and modulation of the so-called P2 responses are similar, irrespective of whether they are obtained with electrodes implanted in the different skin areas or in the various leg muscles. In man it is known that the specific stimulation of cutaneous afferents from different parts of the foot evokes P2 responses, the phase-dependent modulation pattern of which exhibits both location-specific and common features. Responses generally differ, but one striking feature is the occurrence of suppressive responses in the tibialis anterior (TA) of the ipsilateral (i) leg at the end of the swing phase independent of the nerve stimulated. The question arises of whether this aspecificity is limited to the foot. Can similar suppressive P2 responses in iTA be obtained when afferents outside the region of the foot are stimulated during walking? If so this would indicate that there is a very general suppression occurring of input to the TA motor neuron pool, for example through presynaptic inhibition of a corticospinal drive. To answer this type of question the motor responses following transcutaneous stimulation of the rectus femoris (RF) and the motor responses following stimulation of the femoral nerve branch innervating the skin area above the quadriceps were determined during human locomotion. Electromyographic (EMG) activity in iTA was recorded by means of surface electrodes. In all subjects (N=10), the first consistent responses following RF stimulation occurred at about 80 ms poststimulus. The amplitude of these responses showed a clear phase-dependent modulation pattern. Facilitatory responses occurred during the end stance and early swing phase and turned into suppressive responses at the end of the swing phase. To investigate whether cutaneous afferents overlying the RF determined some of the responses following transcutaneous RF stimulation, the experiments were repeated following local anesthesia of the skin under the stimulation electrodes. This did not affect the responses substantially, indicating that most of the RF stimulation results were related to activation of muscle afferents. A similar phase-dependent modulation pattern was found following stimulation of cutaneous afferents of the femoral nerve (Fn). However, this phase-dependent modulation pattern was less pronounced and less consistent over the subjects when compared to the one found following RF stimulation. Our first conclusion is that the results show that P2 reflexes can be elicited both by stimulation of cutaneous afferents in the foot and by proximal cutaneous nerve and muscle stimulation. Secondly, it can be concluded that the suppressive responses at the end of the swing phase are present for both RF stimulation and stimulation of cutaneous afferents of the foot. This result indicates that a wide variety of afferent inputs have a suppressive influence on the input drive to TA motor neurons just prior to heel strike.

Adult↗

PubMed2003

Development of isometric force and force control in children.

Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that optimal performance (in terms of force variability control) closely matches the maturation of the corticospinal tract up to age 10. It was found that maximum voluntary contraction (MVC) matured over the full range of the examined age groups. In contrast, the coefficient of variation of force showed maturation mainly up to the age of 9-10, as hypothesised. Gender differences were found for MVC but not for the other force control parameters. Power spectral density analysis revealed developmental differences in the lower (1-6 and 7-12 Hz) and higher frequencies bands (13-18 and 19-24 Hz). In the lowest frequency range the amount of energy decreased with age, presumably because young children (5-8 years of age) rely more heavily on control from proprioceptive and visual feedback. It is argued that with increasing neural maturation the control processes become more dependent upon internal representation manifested by feed forward control that starts to substitute feedback-based control.

Adult↗

PubMed2003

Distraction affects the performance of obstacle avoidance during walking.

In this study, dual-task interference in obstacle-avoidance tasks during human walking was examined. Ten healthy young adults participated in the experiment. While they were walking on a treadmill, an obstacle suddenly fell on the treadmill in front of their left leg during either midswing, early stance, or late stance of the ipsilateral leg. Participants were instructed to avoid the obstacle, both as a single task and while they were concurrently performing a cognitive secondary task (dual task). Rates of failure, avoidance strategy, and a number of kinematic parameters were studied under both task conditions. When only a short response time was available, rates of failure on the avoidance task were larger during the dual task than during the single task. Smaller crossing swing velocities were found during the dual task as compared with those observed in the single task. The difference in crossing swing velocities was attributable to increased stiffness of the crossing swing limb. The results of the present study indicated that divided attention affects young and healthy individuals' obstacle-avoidance performance during walking.

Adult↗

PubMed2002

Responses of neurons in area VIP to self-induced and external visual motion.

Single-unit recordings were obtained from directionally tuned neurons in area VIP (ventral intraparietal) in two rhesus monkeys under conditions of external (passive) and self-induced (active) visual motion. A large majority of neurons showed significant differences in directional tuning for passive and active visual motion with regard to preferred direction and tuning width. The differences in preferred directions are homogeneously distributed between similar and opposite. Generally, VIP neurons are more broadly tuned to passive than to active visual motion. This is most striking for the group of cells with widely different preferred directions in active and passive conditions. Response amplitudes to passive and active visual motion are not different in general, but are slightly smaller for passive visual motion if the preferred directions differ widely. We conclude that VIP neurons can distinguish between passive and active visual motion.

Animals↗

PubMed2002

Mechanically induced ankle inversion during human walking and jumping.

A new method to study sudden ankle inversions during human walking and jumping is presented. Ankle inversions of 25 degrees were elicited using a box containing a trap door. During the gait task, subjects walked at a speed of 4 km/h. At a pre-programmed delay after left heel strike, an electromagnet released the box on the treadmill. This delay enabled the subject to step on the box without having to change the walking cadence. During the jumping task, subjects jumped from a 30 cm high platform on the box in a standardised way. In both tasks 20 stimulus and 20 control trials were presented randomly. The average tilting velocity of the trap door during the stimulus trials was 403 degrees /s during the walking task and 595 degrees /s during the jumping task. For the control trials a tilting of 0 degrees was used. With this method it is possible to evoke reproducible ankle inversions causing characteristic EMG responses in six lower leg muscles.

Adult↗

PubMed2002

Adaptations in arm movements for added mass to wrist or ankle during walking.

The aim of the present study was to answer the question whether adaptations to local perturbations are restricted to the perturbed limb or whether they induce a reorganization of all co-moving limbs. Specifically, we studied the adaptations in arm movements to mass perturbations in seven healthy adults during walking on a treadmill. Four different perturbation conditions were employed in random order (no perturbation, mass added to both wrists, to the right wrist, and to the right ankle). During each experimental condition ten different belt speeds (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 km/h) were successively offered, while the arm movements and the electromyographic activity of the musculus deltoid posterior and anterior were measured. The results indicated that cadence was not affected by adding mass to the wrist or ankle. However, adding mass to a wrist not only resulted in an increase in muscle activity and a decrease of movement amplitude of the perturbed arm, but also in alterations in the non-perturbed arm. Notably, adding mass to one ankle induced adaptive changes in both arms, in that both muscle activity and arm movement increased. The present results indicate that during walking the loading of one of the limbs induces a general reorganization, involving all participating bodily segments, presumably to maintain balance while providing rhythm constancy.

Adaptation, Physiological↗

PubMed2002

The breakdown of Fitts' law in rapid, reciprocal aiming movements.

According to Fitts' law, there is speed-accuracy trade-off in a wide variety of discrete aiming movements. However, it is unknown whether the same law applies to cyclic aiming movements. In the present study, a comparison is made between discrete versus cyclic aiming movements. A group of 24 healthy participants made graphical pen movements in 12 different aiming tasks in which successive finger and wrist movements were emphasized, consecutively executed as discrete and cyclic movements and varying in three target widths. In the cyclic condition, aiming movements consisted of back-and-forth movements that were performed in immediate succession for 20 s. In the discrete condition, back-and-forth aiming movements were drawn as 20 single strokes, starting after a go signal and stopping after reaching the target area. The targets had various levels of spatial accuracy and the movements had different directions (from lower left to upper right; from lower right to upper left) elicit either predominantly wrist or finger movements. The amount of information processed per unit of time (bits per second; index of performance, IP), tangential velocity, the pen pressure, and the ratio of peak-over-mean velocity were studied to gain understanding about the differences in control between discrete and cyclic movements. It was found that the IP and movement velocity were almost twice as large in cyclic versus discrete movements. In contrast, the axial pen pressure and the ratios of peak-over-mean velocity were much lower in cyclic movements (1.24 N versus 0.94 N; 2.26 N versus 1.81 N). The results of our study indicate that the predicted constant IP does not hold for rapid cyclic aiming movements and that speed-accuracy trade-off is different. It is concluded that cyclic movements exploit the energetic and physiological properties of the neuromotor system. Expected differences in brain activity related to discrete and cyclic aiming movements are discussed as well as several neurophysiological mechanisms, which predict more economic force recruitment and information processing in cyclic than in discrete movements.

Adult↗

PubMed2002

A walking robot called human: lessons to be learned from neural control of locomotion.

From what we know at present with respect to the neural control of walking, it can be concluded that an optimal biologically inspired robot could have the following features. The limbs should include several joints in which position changes can be obtained by actuators across the joints. The control of mono- and biarticular actuators should occur at least at three levels: one at direct control of the actuators (equivalent to motoneuron level), the second at indirect control acting at a level which controls whole limb movement (flexion or extension) and the third at a still higher level controlling the interlimb coordination. The limb level circuits should be able to produce alternating flexion and extension movements in the limb by means of coupled oscillator flexor and extensor parts which are mutually inhibitory. The interlimb control level should be able to command the various limb control centers. All three control levels should have some basic feedback circuits but the most essential one is needed at the limb control level and concerns the decision to either flex or extend a given limb. The decision to activate the extensor part of the limb oscillator has to be based on feedback signalling the onset of loading of the limb involved. This should be signalled by means of load sensors in the limb. The decision to activate the flexor part of the limb oscillator has to depend on various types of feedback. The most important requirement is that flexion should only occur when the limb concerned is no longer loaded above a given threshold. The rule for the initiation of limb flexion can be made more robust by adding the requirement that position at the base of the limb ("hip") should be within a normal end of stance phase range. Hence, human locomotion is thought to use a number of principles which simplify control, just as in other species such as the cat. It is suggested that cat and human locomotion are good models to learn from when designing efficient walking robots.

Animals↗

PubMed2002

Human gait as a step in evolution.

Explore the source record for details and available documents.

Animals↗

PubMed2001

Constraints during bimanual coordination: the role of direction in relation to amplitude and force requirements.

The present study addressed the status of spatial encoding during a bimanual task paradigm. This was based on the premise that patterns of contralateral interference during bimanual coordination provide a window into those movement parameters that are primarily encoded within the central nervous system. Results showed that both direction and amplitude were subject to (bilateral) interference when different specifications were to be generated simultaneously for each limb. Directional interference was found to be partially independent of the amount and pattern of underlying muscle activation, suggesting that direction is encoded at a rather abstract level in the central nervous system. The findings are consistent with single-cell recording studies that have pointed to the role of directional tuning in various brain areas. Moreover, the findings suggest that spatial parameters of movement constrain the coordination of limb movements in addition to temporal parameters.

Adult↗

PubMed2001

Phase-dependent modulation of cutaneous reflexes of tibialis anterior muscle during hopping.

During human gait, the amplitude of cutaneous reflexes in the leg is modulated as a function of the phase of the step cycle. In tibialis anterior (TA) the responses to sural nerve stimulation are facilitatory at end stance while they are suppressive at end swing. To investigate in how far this modulation is specifically related to alternating locomotion, the modulation of such reflexes was studied during a symmetric rhythmic movement, namely hopping (as equivalent of galloping). The end-stance facilitation was present during hopping while the end-swing suppression was absent. It is concluded that the end-stance facilitation is not specific for alternating gait. The absence of the end-swing suppressive reflexes may be related to the absence of heel strike in hopping.

Adult↗

PubMed2001

Brain areas involved in interlimb coordination: a distributed network.

Whereas behavioral studies have made significant contributions toward the identification of the principles governing the coordination of limb movements, little is known about the role of higher brain areas that are involved in interlimb coordination. Functional magnetic resonance imaging (fMRI) was used to reveal the brain areas activated during the cyclical coordination of ipsilateral wrist and foot movements. Six normal subjects performed five different tasks that were presented in a random order, i.e., isolated flexion-extension movements of the right wrist (WRIST) and right foot (FOOT), cyclical coordination of wrist and foot according to the isodirectional (ISODIR) and nonisodirectional (NON-ISODIR) mode, and rest (REST). All movements were auditory paced at 66 beats/min. During the coordination of both limb segments, a distributed network was identified showing activation levels in the supplementary motor area (SMA), cingulate motor cortex (CMC), premotor cortex (PMC), primary sensorimotor cortex (M1/S1), and cerebellum that exceeded the sum of the activations observed during the isolated limb movements. In addition, coordination of the limb movements in different directions was associated with extra activation of the SMA as compared to movements in the same direction. It is therefore concluded that the SMA is substantially involved in the coordination of the nonhomologous limbs as part of a distributed motor network. Accordingly, the long-standing exclusive association that has been made between this medial frontal area and bimanual (homologous) coordination needs to be abandoned and extended towards other forms of interlimb coordination (nonhomologous).

Adult↗

PubMed2001

Postural control and cognitive task performance in healthy participants while balancing on different support-surface configurations.

Postural control during normal upright stance in humans is a well-learned task. Hence, it has often been argued that it requires very little attention. However, many studies have recently shown that postural control is modified when a cognitive task is executed simultaneously especially in the elderly and in the presence of pathology. This study examined postural control modifications when a cognitive task of varying difficulty levels is added. Postural stance difficulty was also varied. Results from this study suggest that a generalized capacity interference may occur due to the larger interference found with the addition of a cognitive task in the more novel and difficult postural task. Because the performance of the cognitive task was tapered by a speed-difficulty trade-off, it was not possible to determine whether a change in the level of difficulty of the cognitive task occurred and if it would produce larger dual-task interference.

Adult↗

PubMed2001

Deterioration of balance control after limb-saving surgery.

OBJECTIVE: Evaluation of the changes in balance control observed in patients after limb-saving surgery for malignant tumors of the lower limb. DESIGN: Case series. RESULTS: In 11 patients who underwent limb-saving surgery and 10 healthy, age-matched controls, displacement of the amplitude of the center of pressure (ACP) and velocity of the center of pressure (VCP) during normal standing and standing on a balance board were registered. Adding such constraints as standing with eyes closed and performing a Stroop task made standing more complex. During normal standing and on the balance board, both groups showed comparable ACP and VCP values. With eyes closed, both patients and controls showed a higher amplitude and velocity in the anterior-posterior direction. In the patient group, the Stroop task affected the ACP (4.5 +/- 0.8 mm) compared with normal standing (2.9 +/- 0.4 mm) and VCP (18.6 +/- 3.0 mm/sec) compared with normal standing (11.9 +/- 1.0 mm/sec). During balance board standing, the authors found a difference in the VCP for both groups whose eyes were closed and who performed under dual-task conditions (controls, 23.2 +/- 3.3 and 14.9 +/- 2.9 mm/sec; patients, 80.1 +/- 12.9 and 23.6 +/- 3.4 mm/sec). CONCLUSIONS: Although the patient group showed impressive upright standing after limb-saving surgery, upright standing become more difficult under higher visual and cognitive loads. This finding indicates that the level of postural automatism is not complete in these patients.

Adolescent↗

PubMed2000

Modulation of cutaneous reflexes by load receptor input during human walking.

To investigate the influence of load on the modulation of cutaneous reflexes, evoked by sural nerve stimulation, electromyographic activity in different leg muscles (tibialis anterior, gastrocnemius medialis (GM), biceps femoris, and soleus muscles (SO)) was recorded in healthy humans during treadmill walking with different body loads. Sural nerve stimulation was applied at two times perception threshold during different phases of the step cycle. Reflex amplitudes increased with body unloading and decreased with body loading. The reflex responses were not a simple function of the level of background activity. For example, in GM and SO, the largest reflex responses occurred during walking with body unloading, when background activity was decreased. Hence, stable ground conditions (body loading) yielded smaller reflexes. It is proposed that load receptors are involved in the regulation of cutaneous reflex responses in order to adapt the locomotor pattern to the environmental conditions.

Adult↗

PubMed2000

Gait and electromyographic analysis of patients recovering after limb-saving surgery.

OBJECTIVE: Control of gait after limb-saving surgery.Design. Case series study. BACKGROUND: At the moment little is known about adaptations in patients' gait after limb-saving surgery. METHODS: Nineteen patients who underwent limb-saving surgery at least 1 yr earlier and 10 normal subjects were studied during treadmill walking. The main outcome measures were walking speed, step parameters and angular displacement of both legs and EMG of the biceps femoris, rectus femoris and medial gastrocnemius in the affected leg. RESULTS: Preferred walking speed in the patients was lower than in the controls (0.7 versus 1.1 m/s). Furthermore, stance phase of the non-affected leg was lengthened. All patients showed reduced stance phase knee flexion in the affected leg, while during the swing phase no difference was seen. The EMG signals of the rectus femoris and biceps femoris show changes, which are related to the location of surgery. CONCLUSIONS: The results showed that the gait pattern of the patients differed compared to normal gait. The reduced stance phase knee flexion in the hip group is based on a high degree of co-contraction between quadriceps and hamstring activity, while in the knee group this is based on the quadriceps avoidance pattern. The finding that there is still side-to-side asymmetry indicates that there is no complete reorganisation following the massive loss of input and output of the leg. It is possible that some reprogramming of the locomotor process occur. RELEVANCE: Gait and electromyographic analysis are essential for the quantitative assessments of the functional outcome in this type of surgery.

Adult↗

PubMed2000

Significance of load receptor input during locomotion: a review.

A basic aspect of the neuronal control of quadrupedal locomotion of cat and of bipedal stance and gait of humans concerns the antigravity function of leg extensors. In humans proprioceptive reflexes involved in the maintenance of body equilibrium depend on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body's centre of mass with respect to the feet. According to observations in the cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait. From these experiments it can be concluded that during locomotion there is a closing of Ib inhibitory and an opening of Ib extensor facilitatory paths. In humans evidence for a significant contribution of load receptor contribution to the leg muscle activation came from immersion experiments. Compensatory leg muscle activation depends on the actual body weight. Also during gait the strength of leg extensor activation during the stance phase is load dependent. In patients with Parkinson's disease there is a reduced load sensitivity and decreased leg extensor activation, which might contribute to the movement disorder. Recent experiments in paraplegic patients show that the beneficial effects of a locomotor training critically depends on the initial degree of body unloading and reloading during the course of the training period.

Animals↗