Mon, Oct 26, 12-1pm
Speaker: Kimberlee Jordan, PhD (Postdoctoral Candidate)
Title: Time dependent structure of variability in physiological time series
Abstract: Variability in human movement has historically been equated with noise in the sensorimotor apparatus, in part because the invariance of movement has traditionally held more interest to scientists that movement variance. Traditional measures of movement variability, such as the Standard Deviation, Coefficient of Variation and Root Mean Square Error provide information regarding the amount of variability in a physiological time series. In contrast, techniques such as Detrended Fluctuation Analysis (Peng et al., 1994) and Approximate Entropy (Pincus 1991) provide information regarding the time dependent structure of fluctuations in the time series.
Increasingly with the use of these techniques it is being recognized that the variability in many physiological time series is not random, and that the degree of predictability of the time series can be indicative of the health of the physiological system in question.
Using Detrended Fluctuation Analysis, the time series of interstride intervals of walking and running in healthy young females was examined. Fluctuations in the interstride interval are not random but contain long range correlations. The strength of the long-range correlations follows a U-shaped function that is centered on the preferred speed of locomotion. Additionally, the discharge rate variability of motor units was examined and was also shown to contain long range correlations, the strength of which are affected by both aging and the gain of visual feedback.
Hosts: Drs. Zev Rymer and Mehdi Mirbagheri
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Fri, Oct 23, 12-1pm
Speaker: Winfried Ilg, PhD
Title: On the locomotion, dynamic stability and rehabilitation of patients with cerebellar ataxia
Abstract: I will present the results of our studies examining (1) the influence of the cerebellum on locomotion and goal-directed leg movements, (2) the phenomenon of velocity-dependent dynamic stability, and (3) the benefits of rehabilitation training for patients with cerebellar disease.
Using a computational method for the quantification of spatio-temporal characteristics of intra-limb coordination patterns, we have been able to identify specific changes in the control and the adaptation of intra-limb coordination for gait in cerebellar patients, which are not predominantly induced by impairments on balance control. In addition, we could show in a study examining patients with focal cerebellar lesions, that the intermediate zone of the cerebellum appears to be of particular importance for limb control on goal-directed leg placement and adaptive locomotion, whereas the medial zone is related to balance control.
Due to the well-known importance of the cerebellum for motor learning and motor adaptation, the benefit of physiotherapeutic training is under dispute for patients with degenerative ataxia.
Impairments of cerebellar patients in (short-term) practice- dependent motor learning have been shown for various motor tasks. Open questions are, whether such patients have lost the ability of practice-dependent motor learning or rather require longer-duration or higher-intensity training to learn. In a controlled clinical study on intensive coordination training, we found first evidence that patients suffering from degenerative cerebellar disease can improve multi-joint coordination and dynamic balance by intensive and continuous coordinative training and thus improve allday-relevant activities.
Host: Dr. Jim Patton |
Fri, Oct 16, 12-1pm
Speaker: Erik Bruun Simonsen, PhD (University of Copenhagen)
Title: Inter-individual differences in H reflex modulation during human walking
Abstract: Based on previous studies, at least two different types of soleus Hoffmann (H) reflex modulation were likely to be found during normal human walking. Accordingly, the aim of the present study was to identify different patterns of modulation of the soleus H reflex and to examine whether or not subjects with different H reflex modulation would exhibit different walking mechanics and different EMG activity. Fifteen subjects walked across two force platforms at 4.5 km/h (+/-10%) while the movements were recorded on video. The soleus H reflex and EMG activity were recorded separately during treadmill walking at 4.5 km/h. Using a two-dimensional analysis joint angles, angular velocities, accelerations, linear velocities and accelerations were calculated, and net joint moments about the ankle, knee and hip joint were computed by inverse dynamics from the video and force plate data. Six subjects (group S) showed a suppressed H reflex during the swing phase, and 9 subjects (group LS) showed increasing reflex excitability during the swing phase. The plantar flexor dominated moment about the ankle joint was greater for group LS. In contrast, the extensor dominated moment about the knee joint was greater for the S group. The hip joint moment was similar for the groups. The EMG activity in the vastus lateralis and anterior tibial muscles was greater prior to heel strike for the S group. These data indicate that human walking exhibits at least two different motor patterns as evaluated by gating of afferent input to the spinal cord, by EMG activity and by walking mechanics. Increasing H reflex excitability during the swing phase appears to protect the subject against unexpected perturbations around heel strike by a facilitated stretch reflex in the triceps surae muscle. Alternatively, in subjects with a suppressed H reflex in the swing phase the knee joint extensors seem to form the primary protection around heel strike.
Host: Maria Knikou |
Thu, Oct 15, 2-3pm
Speaker: Dr. Penelope McNulty, BHMS (Hons), PhD (Prince of Wales Medical Research Institute in Australia)
Title: The recruitment order of single motor units in human muscles.
Abstract: Single motor units are generally activated during voluntary contractions with a stereotypical progressive recruitment order from the slowest, weakest units to stronger, larger motor units. While this principle is generally accepted for voluntary contractions it is often assumed that recruitment order is reversed by electrical stimulation. We examined the recruitment order of single motor units in a series of studies during voluntary contractions and in response to electrical stimulation. The exceptions to the orderly recruitment of single motor unit during targeted voluntary contractions reported for diaphragm motor units could not be demonstrated in limb muscles. Single motor unit activity was recorded in first dorsal interosseous muscle using an intramuscular concentric needle electrode during tasks with either a constant velocity to different displacements, or a constant displacement at different velocities. The shuffle index allowed us to quantify the recruitment order variability of single motor units (n=114) at 14 recording sites in 8 subjects. Significant variability in the recruitment order of single motor units was seen both within and between tasks, similar to that reported for the diaphragm but no systematic shuffling of motor unit recruitment order was observed.
A combination of experimental data and mathematical modelling was used to investigate the recruitment order of electrically stimulated motor units in tibialis anterior (n=20) and brachioradialis (n=6) muscles. Detailed stimulus response curves showed that the experimental and modelled data were closely matched with correlation coefficients ranging from 95.3-99.8. Motor units were recruited during electrical stimulation following a complex pattern that neither follows a strict Henneman size principle nor a simple reverse of that order. It is important to understand the recruitment order of motor units so that we can interpret the data from disordered physiology.
We compared the results of our modelling study to the detailed stimulus response curves recorded in a similar manner from the tibialis anterior muscle of 16 spinal cord injury (SCI) patients. Some muscles demonstrated a gross reduction in motor unit numbers while others did not differ from the able bodied. Abnormalities were also noted in the recruitment pattern of motor units in SCI affected muscles. These results suggest that traditional methods of motor unit number estimations may not reflect the number or combination of changes that affect surviving motor units in chronic SCI.
Host: Dr. Zev Rymer
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Mon, Oct 12, 12:30pm - 1:30pm
Speaker: James Sulzer (PhD Candidate)
Title: Improving knee flexion for people with stiff-knee gait after stroke
Abstract: The inability to adequately bend the knee during swing phase of walking, known as Stiff-Knee gait (SKG), commonly occurs after stroke. It is believed other compensatory, energy-consuming kinematics such as pelvic obliquity and hip abduction accompany the "stiff" knee to help clear the foot. Models have shown that improving knee flexion torque before the paretic limb leaves the ground will result in greater knee flexion angle during swing, thus greater foot clearance. If these gait compensations are motivated by foot clearance, then assisting pre-swing knee flexion torque will reduce gait compensations.
To pursue this hypothesis, we needed a lightweight, backdrivable knee actuator. After finding existing actuators insufficient, we developed a concept that remotely controlled deflection of a compliant spring through a sheathed cable. This concept was developed into a knee flexion actuator capable of selectively applying torque during gait. Its performance characteristics made this device, known as SERKA (Series Elastic Remote Knee Actuator), optimally suited to our needs.
We examined the effect of knee flexion assistance on gait compensations in nine stroke subjects, examining changes in peak knee flexion angle, hip abduction and pelvic obliquity. The results were compared to the controls ran earlier. Stroke subjects significantly increased hip abduction during assistance instead of the predicted decrease, with no change in controls. We infer that this is due to abnormal coordination, which may be a primary cause of gait impairment after stroke. In conclusion, assistive technology and rehabilitation science must account for less visible neural issues when addressing people with neurological disabilities. We hope this work inspires others to investigate underlying mechanisms of disease states and their modes of neural control en route to rehabilitation and assistive device development.
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Wed, Oct 7, 12-1pm
Speaker: Emily Keshner, PT, EdD
Title: Does Visual-Vestibular Conflict Reveal an Internal Model for Spatial Orientation?
Abstract: Visual field motion has been linked to postural behavior and orientation in space is governed by an interaction between the visual and vestibular systems. The sensory reweighting model predicts that as the velocity of visual motion becomes less relevant to physical motion, then subjects would exhibit a lesser response to visual motion and an increased sensitivity to their physical inputs. We have found that even when visual field motion is inappropriate for self-motion, reorganized postural behaviors emerge to compensate for the visual disturbance. In this talk I will present results of experiments suggesting that sensory reweighting may be a local phenomenon, defined by the momentary sensory array, which allows us to modify the internal model for spatial orientation.
Host: Sandro Mussa-Ivaldi
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Thu, Oct 1, 2-3pm
Speaker: Maxim Klesnikov
Title: Improving the Realism of Haptic Interaction For Teaching of Sensorimotor Skill
Abstract: Recently, haptic simulators have shown great potential in teaching sensorimotor skills. This is especially true for areas where the traditional training technique is expensive, such as medical and dental training. This talk addresses two areas where improvement is needed to increase the realism of haptic interaction and the effectiveness in teaching of sensorimotor skills. The first part of the talk is about haptic rendering algorithms. Modern penalty-based haptic rendering algorithms do not produce realistic forces in certain situations. A new method for haptic rendering is implemented based on physics rather than on heuristics. At the same time the new method is fast enough to be executed in the allowed time frame. The second part of the talk deals with the problem of recording haptically augmented training videos. This provides a way to convey the information necessary to master a new skill from a teacher to a trainee. Several haptic playback schemes are proposed. The talk will conclude with the description of PerioSim, a haptic virtual reality simulator for sensorimotor skill acquisition in dentistry.
Hosts: Sandro Mussa-Ivaldi and Kevin Lynch
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Thu, Sept 10, 2-3pm
Speaker: Daniel Corcos, PhD
Title: Translational Neuroscience and the Treatment of Parkinson's Disease
Abstract: Parkinson's disease is a progressive neurological disorder that is associated with motor and nonmotor impairments. Long-term treatment with dopaminergic therapy is often associated with major negative side effects that result in further impairment. The effective treatment of Parkinson's disease will benefit from markers that help to detect the disease early, diagnose the disease accurately, and develop new therapies that reduce the amount of dopaminergic medication required by patients. The first part of this talk will outline a new biomarker for Parkinson's disease. The second part will present preliminary data from a two-year study of progressive resistance exercise for individuals with Parkinson's disease. The talk will conclude with the presentation of some recent data on the effects of five years of stimulating the subthalamic nucleus on the cardinal signs of Parkinson's disease.
Host: Sandro Mussa-Ivaldi
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Wed, Sept 2, 12-1pm
Speaker: Kiyoshi Okawa (Honda R&D Co., Ltd.)
Title: Honda Walking Assist Device (Stride Management Assist)
Abstract: Walking dysfunction represents a serious threat to elderly. As early as 1999, the Fundamental Technology Research Center at Honda R&D Co., Ltd. began research on walking assist technology to help improve the progressive decline in lower extremity motor abilities in the elderly. An early test model created in 2000 weighed approximately 70-lbs and was bulky, but following numerous prototypes and thousands of hours of testing, by 2007 the weight had been reduced to just 6-lbs. Many currently available research devices for walking provide assistance through an increase in power at various joint axis, while the walk assist device assists movement based on a cooperative control principle where only the hip joint axis is equipped with a small motor, which generates assist force. Due to its simple construction and light weight, the device can be used in any public or social environment without one feeling self-conscious or uncomfortable.
During its operation a user’s walking pace is monitored through hip angle sensors and this information is fed to a control computer which applies cooperative control and calculates the amount and timing of assist to be provided. The torque generated by the motors is transmitted to the thighs through the frames thus serving to lengthen the user’s stride and resulting in optimal and enjoyable walking assist. Further, as the walking stride is lengthened, muscle activity around the hip area and lower legs increases. When used continuously over a period of time, test results have shown that the user maintains a longer and smoother walking stride even when the device is not worn. The device has been successfully tested in providing walking assistance in the elderly in Japan. A wide range of applications is conceivable, but in Japan, it is hoped that the device will be useful in walking rehabilitation. Currently, the validity of this device in the rehabilitation and recovery of walking in individuals with stroke and other neurological dysfunctions is being investigated.
Hosts: Drs. Zev Rymer and Arun Jayaraman |
Fri, Aug 28, 12-1pm
Speaker: Jungwha "Julia" Lee, PhD
Biostatistician, Biostatistics Collaboration Center, Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University
Title: Statistical power analysis and sample size estimation
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Fri, Aug 21, 12-1pm
SMPP postdoc grant proposal presentation
Speakers: Keith Gordon, Claire Honeycutt & Ann Simon
SMPP postdoctoral fellows will present their grant proposals covering specific aims, design and key methods (5 minute presentation plus 5 minute discussion per proposal). The main purpose of the meeting is to provide feedback on postdoc grants from a non-expert audience, and give postdocs an opportunity to defend their proposed study.
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Fri, Aug 14, 12-1pm
SMPP postdoc seminar
Speaker: Kunlin Wei
SMPP postdoctoral fellows will present their grant proposals covering specific aims, design and key methods (5 minute presentation plus 5 minute discussion per proposal). The main purpose of the meeting is to provide feedback on postdoc grants from a non-expert audience, and give postdocs an opportunity to defend their proposed study.
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Thu, Aug 6, 12-1pm
Speaker: Todd Murphey, PhD (Assistant Professor, Mechanical Engineering, Northwestern University)
Title: Variational Methods for Hand Analysis and Simulation
Abstract: I will discuss numerical modeling techniques for dynamically modeling a human hand. We use a strand-based method of modeling the muscles and tendons. Our technique represents a compromise between capturing the full dynamics of the tissue mechanics and the need for computationally efficient representations for control design and multiple simulations appropriate for statistical planning and optimization tools. We show how to derive a strand-based model in a variational integrator context. Variational integrators are particularly well-suited to resolving closed-kinematic chains, making them appropriate for hand modeling. We demonstrate the technique with a hand model comprised of 19 rigid bodies and 23 muscle strands engaged in a grasp of an object. Moreover, we can compute the linearization of the hand dynamics around nominal trajectories allowing us to compute locally optimal control laws in the linear quadratic regulator (LQR) sense.
I will end with a discussion of future work, including the need for local robustness analysis, impact handling, surface friction representations, and system identification.
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Mon, August 3, 4-5pm
Magnuson Auditorium (16th Floor)
Speaker: David Reinkensmeyer, PhD
Title: How do people respond to robot assistance during motor training?
Abstract: There has been a rapid increase in the last ten years in the number of research groups and companies that are developing robotic devices to partially automate motor rehabilitation following neurologic injuries like stroke and spinal cord injury. A common approach is to design the robotic therapy device to physically assist the patient in making desired movements, mimicking the approach of "active assistance" sometimes used by rehabilitation therapists. In this talk, I will show that the motor system responds to such assistance differently for different movement tasks. For training of reaching movements, most clinical studies of robot therapy to date suggest that assistance neither hinders nor improves motor recovery. Rather, its primary benefit may be to provide a more motivating training environment. These findings bring into question the Hebbian-like conceptual framework of motor plasticity that is sometimes used to provide a scientific rationale for robot-assisted therapy. For training of walking, robot assistance allows a patient to practice faster, more natural looking movements more safely, but there is evidence it sometimes hinders recovery. This may be because the human locomotor system systematically "slacks" when given the opportunity. In a third application we are currently developing - teaching children with a severe disability to drive a powered wheelchair - we recently found that robotic assistance enhanced motor learning in a pilot study with non-disabled children. Understanding the neural mechanisms that elicit these differing responses - indifference, slacking, and enhancement - is essential for determining whether and how robots can actually be useful in rehabilitation practice.
Host: Sandro Mussa-Ivaldi
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