Biomedical subjects

Thomas Sinkjaer

Publications and source records attributed to Thomas Sinkjaer.

At least 19 recordsLinked to original sources

PubMed2006

Associative plasticity in human motor cortex during voluntary muscle contraction.

TMS pulses over the hand area of motor cortex activate different subpopulations of synaptic connections if the direction of the induced current in the brain is reversed from posterior-anterior (PA) direction to anterior-posterior (AP). We tested whether this also made a difference to the after-effects of paired associative stimulation (PAS: ulnar nerve stimulation followed 25 ms later by a transcranial magnetic stimulation pulse). If 50 pairs of stimuli (0.1 Hz) were applied using conventional suprathreshold PA-PAS in resting subjects, there was no effect on motor-evoked potentials (MEPs) in the first dorsal interosseous muscle. In contrast if the same number of pulses were given while subjects made a small tonic (5% maximum) contraction, MEPs were facilitated and resting motor threshold reduced when AP but not PA pulses were used. Subsequent experiments employed subthreshold TMS (95% of the active motor threshold) during voluntary muscle contraction. MEP facilitation accompanied by reduced AP threshold occurred when PAS was given using AP pulses (AP-Sub-PAS), whereas PAS using PA pulses (PA-Sub-PAS) had no excitatory effect. There was no facilitation if the ulnar nerve stimulus was replaced by digital nerve stimulation. There was a tendency for short interval intracortical inhibition (SICI) to decrease and intracortical facilitation (ICF) to increase after AP-Sub-PAS. We propose that the increased effectiveness of AP-Sub-PAS over PA-Sub-PAS is due to the fact that AP TMS more readily activates I3 inputs to corticospinal neurons and hence that these are an important component of associative plasticity in the human motor cortex.

Adult↗

PubMed2006

Afferent-mediated modulation of the soleus muscle activity during the stance phase of human walking.

The aim of this study was to investigate the contribution of proprioceptive feedback to the amplitude modulation of the soleus muscle activity during human walking. We have previously shown that slow-velocity, small-amplitude ankle dorsiflexion enhancements and reductions applied during the stance phase of the step cycle generate, respectively, increments and decrements on the ongoing soleus activity. We have also shown that the increments in soleus activity are at least partially mediated by feedback from group Ia fibres. In the present study, we further investigated the afferent-mediated contribution from muscle group II afferents, cutaneous and proprioceptive afferents from the foot, and load-sensitive afferents to the soleus EMG. Slow-velocity, small-amplitude ankle trajectory modifications were combined with the pharmaceutical depression of group II polysynaptic pathways with tizanidine hydrochloride, anaesthetic blocking of sensory information from the foot with injections of lidocaine hydrochloride, and modulation of load feedback by increasing and decreasing the body load. The depression of the group II afferents significantly reduced the soleus response to the ankle trajectory modifications. Blocking sensory feedback from the foot did not have an effect on the soleus muscle activity. Changes in body load affected the ongoing soleus activity level; however, it did not affect the amplitude of the soleus EMG responses to the ankle trajectory modifications. These results suggest that the feedback from group II afferents, and possibly from load-sensitive afferents, contribute to the amplitude modulation of the soleus muscle activity during the stance phase of the step cycle. However, feedback from cutaneous afferents and instrinsic proprioceptive afferents from the foot does not seem to contribute to this muscle activation.

Adult↗

PubMed2006

Event driven electrical stimulation of the dorsal penile/clitoral nerve for management of neurogenic detrusor overactivity in multiple sclerosis.

AIMS: The aim of this study was to evaluate the effect of automatic event driven electrical stimulation on the dorsal penile/clitoral nerve for management of neurogenic detrusor overactivity in patients suffering from Multiple Sclerosis. METHODS: A total of 10 patients participated in the study. Detrusor pressure was recorded during physiological filling of the bladder and electrical stimulation was applied with surface electrodes whenever the detrusor pressure exceeded 10 cm H(2)O. RESULTS: In seven of the eight patients, where neurogenic detrusor overactivity was observed an average of 12 detrusor contractions could be inhibited by stimulation. In one patient, however, stimulation failed to inhibit the detrusor contractions. The average increase in bladder volume from first suppressed detrusor contraction until leakage was 94% (range: 22-366%). On average, the time from first suppressed contraction until leakage was 15 min and 50 sec (range: 4 min 58 sec-32 min 5 sec) with an average physiological filling rate of 8 ml/min. Urgency was effectively suppressed at the onset of stimulation. CONCLUSIONS: The results indicate that involuntary detrusor contractions in patients with multiple sclerosis can effectively be inhibited with event driven stimulation, hereby improving bladder capacity and reducing the number of incontinence episodes. However, the used method for detecting detrusor contractions is not suitable in a chronic setting and alternative techniques needs to be investigated if stimulation should be applied automatically.

Adult↗

PubMed2006

The effect of repetitive electrical stimulation on the motor evoked hemodynamic responses.

The aim of this study was to investigate the influence of short-term repetitive electrical stimulation (rES training session) on the motor-evoked hemodynamic responses. The fMRI echo-planar images (EPI) were recorded before and after the rES training. The right median nerve (MN) was stimulated during rES. The rES training resulted in a significant increase in activity in a number of supraspinal regions, including sensorimotor and associative cortical areas. On the subcortical level, the effect was also found in the cerebellum, the midbrain, and the thalamus. Possible mechanisms of the neuronal plastic changes observed after rES, and memory processes involved in learning are discussed.

Adult↗

PubMed2005

Motor cortex excitability following repetitive electrical stimulation of the common peroneal nerve depends on the voluntary drive.

Previously, long-term changes in the motor cortex have been reported after repetitive electrical nerve stimulation (rES) as well as after motor exercise. The purpose of this study was to investigate whether the effects of voluntary motor cortical drive and of rES on the motor cortical output in healthy subjects interact with each other. A 30-min exercise session was performed during the following conditions: rES of the right common peroneal nerve (CPN) during rES at rest (A); voluntary exercise of the right ankle dorsiflexors alone (B); rES combined with voluntary dorsiflexion exercise (C); voluntary exercise of ankle plantar flexors alone (D); and plantar flexion exercise combined with rES (E). Motor evoked potentials (MEPs) were obtained before and after the exercise with a stimulation intensity of 125% of the threshold of the relaxed right tibialis anterior (TA). rES was ON for 1 s and OFF for 2 s in a cycle, and consisted of trains of five pulses, duration 1 ms and frequency 30 Hz, as applied in functional electrical stimulation (FES). MEPs of the TA muscle elicited after the training were increased in A by 38%, in B by 35%, and in C by 66%. In D and E, the MEPs of TA were decreased by 29% and 35%, respectively. The effect was maintained for at least 30 min after the nerve stimulation was completed. Consistent with previous studies (Khaslavskaia et al. (2002) Exp Brain Res 145:309-315), MEPs after the CPN rES are shown to be partly due to increased TA cortical excitability. These results suggest that the effect of FES on motor cortical excitability depends on the concurrent motor cortical drive present at the time of FES, and the combination of these factors modulates neural excitability and probably reorganization. The decrease in motor cortical excitability after plantar flexor exercise probably means that voluntary effort antagonistic to the electrical exercise is stronger and cancels out the effects of rES. Improving FES effects through an agonist voluntary drive implies an enhancement of sensorimotor reorganization through the addition of a voluntary component to a trained movement. Possible mechanisms and implications of these results on the rehabilitation of patients with paralysis and spasticity are discussed.

Adaptation, Physiological↗

PubMed2005

Lack of on-going adaptations in the soleus muscle activity during walking in patients affected by large-fiber neuropathy.

The aim of this study was to investigate the contribution of feedback from large-diameter sensory fibers to the adaptation of soleus muscle activity after small ankle trajectory modifications during human walking. Small-amplitude and slow-velocity ankle dorsiflexion enhancements and reductions were applied during the stance phase of the gait cycle to mimic the normal variability of the ankle trajectory during walking. Patients with demyelination of large sensory fibers (Charcot-Marie-Tooth type 1A and antibodies to myelin-associated glycoprotein neuropathy) and age-matched controls participated in this study. The patients had absent light-touch sense in the toes and feet and absent quadriceps and Achilles tendon reflexes, indicating functional loss of large sensory fibers. Moreover, their soleus stretch reflex response consisted of a single electromyographic (EMG) burst with delayed onset and longer duration (P < 0.01) than the short- and medium-latency reflex responses observed in healthy subjects. In healthy subjects, the soleus EMG gradually increased or decreased when the ankle dorsiflexion was, respectively, enhanced or reduced. In the patients, the soleus EMG increased during the dorsiflexion enhancements; however, the velocity sensitivity of this response was decreased compared with the healthy volunteers. When the dorsiflexion was reduced, the soleus EMG was unchanged. These results indicate that the enhancement of the soleus EMG is mainly sensitive to feedback from primary and secondary muscle spindle afferents and that the reduction may be mediated by feedback from the group Ib pathways. This study provides evidence for the role of sensory feedback in the continuous adaptation of the soleus activity during the stance phase of human walking.

Adaptation, Physiological↗

PubMed2005

Colon emptying induced by sequential electrical stimulation in rats.

Electrical stimulation could be used to induce colon emptying. The present experiments were performed to establish a stimulation pattern to optimize the stimulation parameters and to test neural involvement in propulsion induced by electrical stimulation. Colon segments were sequentially stimulated using rectangular pulses. The resulting propulsive activity displaced intraluminal content in consecutive propulsion steps. The propulsion steps differed in displacement latency, distance, and velocity along the stimulated colon. Increasing the pulse duration or amplitude resulted in a decrease of the latency. Increasing the stimulation amplitude doubled the displacement distance. The frequencies tested in the present study did not affect propulsion. Inhibition of cholinergic and nitrergic pathways inhibited propulsion. Electrical stimulation can induce colonic propulsion. Motor differences are present along the descending colon. The most suitable combination of pulse parameters regarding colon stimulation is 0.3 ms, 5 mA, 10 Hz. Neural circuits are involved in propulsion when using these values.

Animals↗

PubMed2005

Intraoperative recording of sacral root nerve signals in humans.

Electroneurographic signals were intraoperatively recorded from the S3 sacral nerve root in two SCI patients. The aim of this study was to record afferent nerve signals in response to mechanical stimulation of the urinary bladder, rectum, and dermatome. Such signals could be used in an implantable neuroprosthesis to treat neurogenic detrusor overactivity. In both patients a neural response was recorded from the dermatome and the rectum, but from the bladder only in one patient. The results were consistent with results from animal and other human studies. Further studies are however, needed because the number of subjects investigated remains low.

Adult↗

PubMed2005

Electrical stimulation to induce propulsive contractions in the porcine descending colon.

Electrical stimulation of the colon can improve transit in slow-transit constipation, or enable controlled emptying in colostomy patients. Preliminary studies showed that sequential stimulation of consecutive colon segments induced serial contractions resulting in colonic propulsion. This study was performed to optimize the stimulation parameters. The electrodes were inserted under the serosa of the descending colon of pigs. Charge-balanced rectangular pulses at 10 Hz were delivered in consecutive sessions. Electrically evoked contractions (ECs) were monitored using impedance planimetry and manometry. The luminal pressure and cross-sectional area (CSA), the latency and velocity of CSA decrease, and the wall tension were compared for ECs induced using 3 ms pulses of 9, 12, 15, and 30 mA. When using 15 mA, ECs induced by 0.03, 0.3, and 3 ms long pulses were compared. A current increase from 9 to 30 mA induced a significant increase in the pressure generated by contraction. The increase in pulse duration from 0.03 to 3 ms resulted in shorter latency, faster contraction, higher pressure, and higher wall tension. It is concluded that, at a frequency of 10 Hz, the best combination of current and pulse duration to elicit propulsive contractions in the descending colon of pigs is 15 mA and 3 ms.

Animals↗

PubMed2004

Contribution of afferent feedback to the soleus muscle activity during human locomotion.

During the stance phase of the human step cycle, the ankle undergoes a natural dorsiflexion that stretches the soleus muscle. The afferent feedback resulting from this stretch enhances the locomotor drive. In this study a robotic actuator was used to slightly enhance or reduce the natural ankle dorsiflexion, in essence, mimicking the small variations in the ankle dorsiflexion movement that take place during the stance phase of the step cycle. The soleus (SOL) and tibialis anterior EMG were analyzed in response to the ankle trajectory modifications. The dorsiflexion enhancements and reductions generated gradual increments and decrements, respectively, in the ongoing SOL EMG. We exercised care to ensure that the imposed ankle movements were too slow to elicit distinct burst-like stretch reflex responses that have been investigated previously. The increased SOL EMG after the dorsiflexion enhancements was reduced when the group Ia afferents were blocked with peripheral ischemia at the thigh, and during high-frequency Achilles tendon vibration. However, neither ischemia nor tendon vibration affected the decrements in the SOL EMG during the dorsiflexion reductions. These findings give evidence of the contribution of afferent feedback to the SOL activity in an ongoing basis during the stance phase. The results suggest that mainly feedback from the group Ia pathways is responsible for the increments in the SOL EMG during the dorsiflexion enhancements. However, the decrements in the SOL activity might be mediated by different afferent mechanisms.

Adult↗

PubMed2004

The suppression of the long-latency stretch reflex in the human tibialis anterior muscle by transcranial magnetic stimulation.

The purpose of this study was to investigate the transcortical nature of the long-latency stretch reflex (M3) in the human tibialis anterior muscle. This was achieved by applying a single pulse of subthreshold (90% motor threshold) transcortical magnetic stimulation (subTMS) at the site of the motor cortex. Such a stimulus is able to activate intracortical inhibitory circuits and thereby depress motor cortical output. We hypothesized that it would also suppress a transcortical reflex loop. The stretch reflex was elicited using a pedal attached to an electric motor. SubTMS was applied at several intervals prior to M3. Recordings were repeated 20-40 times. The reflex components were quantified using 20-ms windows in the averaged rectified electromyogram (EMG). SubTMS evoked significantly larger depression of M3 than of the background EMG in the same time frame when applied 55-85 ms prior to M3 ( P<0.05, n=10). Furthermore, the effect on M3 was significantly larger than the effect on the spinal M2 ( P<0.01, n=7). Our results provide evidence that the long-latency stretch reflex in the tibialis anterior muscle is at least partly transcortical.

Adult↗

PubMed2004

Evaluating robustness of gait event detection based on machine learning and natural sensors.

A real-time system for deriving timing control for functional electrical stimulation for foot-drop correction, using peripheral nerve activity as a sensor input, was tested for reliability to investigate the potential for clinical use. The system, which was previously reported on, was tested on a hemiplegic subject instrumented with a recording cuff electrode on the Sural nerve, and a stimulation cuff electrode on the Peroneal cuff. Implanted devices enabled recording and stimulation through telelinks. An input domain was derived from the recorded electroneurogram and fed to a detection algorithm based on an adaptive logic network for controlling the stimulation timing. The reliability was tested by letting the subject wear different foot wear and walk on different surfaces than when the training data was recorded. The detection system was also evaluated several months after training. The detection system proved able to successfully detect when walking with different footwear on varying surfaces up to 374 days after training, and thereby showed great potential for being clinically useful.

Action Potentials↗

PubMed2003

Biopotentials as command and feedback signals in functional electrical stimulation systems.

Today Functional Electrical Stimulation (FES) is available as a clinical tool in muscle activation used for picking up objects, for standing and walking, for controlling bladder emptying, and for breathing. Despite substantial progress in development and new knowledge, many challenges remain to be resolved to provide a more efficient functionality of FES systems. The most important task of these challenges is to improve control of the activated muscles through open loop or feedback systems. Command and feedback signals can be extracted from biopotentials recorded from muscles (Electromyogram, EMG), nerves (Electroneurogram, ENG), and the brain (Electroencephalogram (EEG) or individual cells). This paper reviews work in which EMG, ENG, and EEG signals in humans have been used as command and feedback signals in systems using electrical stimulation of motor nerves to restore movements after an injury to the Central Nervous System (CNS). It is concluded that the technology is ready to push for more substantial clinical FES investigations in applying muscle and nerve signals. Brain-computer interface systems hold great prospects, but require further development of faster and clinically more acceptable technologies.

Action Potentials↗

PubMed2003

Quantification of hyperreflexia in amyotrophic lateral sclerosis (ALS) by the soleus stretch reflex.

UNLABELLED: The aim of this study was to quantify upper motor neuron (UMN) involvement in amyotrophic lateral sclerosis (ALS) by the soleus stretch reflex. METHODS: In a group of 24 ALS patients and ten healthy controls the soleus stretch reflex was elicited by a four degree rotation at the ankle joint. Amplitude of the short-latency stretch reflex, threshold, and sensitivity were determined. Peripheral excitation/contraction properties were evaluated by supramaximal stimulation of the tibial nerve. Clinical scores of upper motor neuron involvement were applied. RESULTS: A highly significant correlation between threshold and sensitivity of the stretch reflex and clinical score of upper motor neuron involvement was found; patients with a low threshold and a high sensitivity in general had a high upper motor neuron score. CONCLUSION: It is suggested that upper motor neuron involvement in ALS can be evaluated by using the soleus stretch reflex. This may be useful in monitoring progression of the disease and evaluating new therapies.

Adult↗

PubMed2003

Mobile ankle and knee perturbator.

A mobile ankle and knee perturbator has been developed. It consists of a functional joint with an integrated clutch. Four Bowden wires connect the joint to a powerful motor and a double pneumatic cylinder. When needed during any time of the gait cycle, it is possible to impose an ankle rotation by engaging the clutch and rotating the ankle or knee joint with a predefined displacement. The system is designed to investigate electrophysiological and biomechanical features of the human ankle or knee joint during gait.

Adult↗

PubMed2003

On the intersubject generalization ability in extracting kinematic information from afferent nervous signals.

In the recent past, many efforts have been carried out in order to evaluate the feasibility of implementing closed-loop controlled neuroprostheses based on the processing of sensory electroneurographic (ENG) signals. The success of these techniques mostly relies on the development of processing algorithms capable of extracting the necessary kinematic information from these signals. Soft-computing algorithms can be very useful when dealing with the complexity of the neuromuscular system because of their generalization ability and model-free structure. In this paper, these techniques were used to extract angular position information from the ENG signals recorded from muscle afferents in animal model using cuff electrodes. Specifically, a genetic algorithm-based dynamic nonsingleton fuzzy logic system (named GA-DNSFLS) was developed and tested on different types of angular trajectories (characterized by small or large angular excursions). In particular, two different Takagi-Sugeno-Kang (TSK)-like structures were used in the consequent part of the neuro-fuzzy model in order to verify which one could improve the generalization abilities (intrasubject and intersubject). The results showed that the GA-DNSFLS was able to reconstruct the trajectories giving interesting results in terms of correlation between the actual and the predicted trajectories for small excursion movements during intrasubject and intersubject tests. Particularly, one of the TSK models showed better results in terms of intersubject generalization. The simulations conducted with the large excursion movements led in some cases to interesting results but further experiments are necessary in order to analyze this point more in deep.

Action Potentials↗

PubMed2003

BalanceReTrainer: a new standing-balance training apparatus and methods applied to a chronic hemiparetic subject with a neglect syndrome.

In this paper we present a mechanical apparatus and methods named BalanceReTrainer for standing-balance training in neurologically impaired individuals. BalanceReTrainer provides an impaired individual with a fall-safe balancing environment, where the balancing efforts of a standing individual are augmented by stabilizing forces acting at the level of pelvis in the sagittal and frontal planes of motion, assisting the balancing activity ankle and hip muscles and at the level of shanks, assisting the knee extensor muscles. A range of different levels of supporting forces is generated by passive, compliant means. Additionally, movement in the sagittal and frontal planes, acquired by transducers is fed to an electronic interface which transforms the current inclinations into a computer mouse signals, which are interfaced to a personal computer (PC) where balance training and evaluation program is running. The level of stiffness support and level of difficulty of computer task can be selected according to current balancing abilities of the impaired individual. We further present results of a case study where an ambulatory chronic hemiparetic subject with neglect syndrome received ten days of balance training on BalanceReTrainer. Biomechanical evaluation of weight-shifting activity before and after treatment shows a substantial functional improvement.

Adult↗

PubMed2002

Increase in tibialis anterior motor cortex excitability following repetitive electrical stimulation of the common peroneal nerve.

The purpose of this study was to investigate whether repetitive electrical stimulation of the common peroneal nerve (CPN) is associated with changes in the motor response of the tibialis anterior (TA) muscle elicited by focal magnetic stimulation of the motor cortex. Motor evoked potentials (MEP) with a stimulation intensity of 125% of the threshold of the relaxed right TA were obtained before, during, and after repetitive electrical stimulation of the CPN (trains of five pulses of 1 ms, at a frequency of 200 Hz, repeated every second with a 30-min duration). The MEP of the TA muscle elicited after repetitive electrical stimulation were increased by 104% (range: 18-263%), and the increase was maintained for up to 110 min (range: 15-110 min) after the end of nerve stimulation. This increase in the MEP of the TA muscle was associated with a decrease in the threshold from the stimulation-response curve. Furthermore, during that period the early component of the TA stretch reflex as well as the latency of the MEP did not significantly change. To further test the origin of the increased MEP, complementary experiments showed that MEP elicited by transcranial electrical stimulation (TES) were also increased, but to a lesser degree (approximately 50%) than MEP elicited by TMS. It can be concluded that short-term nerve repetitive electrical stimulation of the lower extremities in healthy human participants can lead to a long-term increase in the contralateral MEP. As TES is believed to mainly activate the axon and not the soma of the cortical cells, the increased MEP cannot be explained exclusively by changes in the motor cortex cell excitability, but also by changes in subcortical neural structures involved in the excitation of spinal motoneurons. The results of this study allow the speculation that it would be possible to use repetitive electrical stimulation in the rehabilitation of patients with lower limb muscle weakness and spasticity.

Adult↗