Postural instability via a loss of intermittent control in elderly and patients with Parkinson's disease: a model-based and data-driven approach

Postural instability is one of the major symptoms of Parkinson's disease. Here, we assimilated a model of intermittent delay feedback control during quiet standing into postural sway data from healthy young and elderly individuals as well as patients with Parkinson's disease to elucidate the possible mechanisms of instability. Specifically, we estimated the joint probability distribution of a set of parameters in the model using the Bayesian parameter inference such that the model with the inferred parameters can best-fit sway data for each individual. It was expected that the parameter values for three populations would distribute differently in the parameter space depending on their balance capability. Because the intermittent control model is parameterized by a parameter associated with the degree of intermittency in the control, it can represent not only the intermittent model but also the traditional continuous control model with no intermittency. We showed that the inferred parameter values for the three groups of individuals are classified into two major groups in the parameter space: one represents the intermittent control mostly for healthy people and patients with mild postural symptoms and the other the continuous control mostly for some elderly and patients with severe postural symptoms. The results of this study may be interpreted by postulating that increased postural instability in most Parkinson's patients and some elderly persons might be characterized as a dynamical disease

Lateral hypothalamic activity indicates hunger and satiety states in humans

Lateral hypothalamic area (LHA) local field potentials (LFPs) were recorded in a Prader–Willi patient undergoing deep brain stimulation (DBS) for obesity. During hunger, exposure to food-related cues induced an increase in beta/ low-gamma activity. In contrast, recordings during satiety were marked by prominent alpha rhythms. Based on these findings, we have delivered alphafrequency DBS prior to and during food intake. Despite reporting an early sensation of fullness, the patient continued to crave food. This suggests that the pattern of activity in LHA may indicate hunger/satiety states in humans but attest to the complexity of conducting neuromodulation studies in obesity

Neuromuscular Control of the Trunk during Sitting Balance

Sitting stability is maintained by continuous and intermittent activation of trunk and lower limb muscles. However, spinal cord injury (SCI) can result in paralysis of the trunk muscles and affects sitting balance. Currently, chest straps and trunk braces are used to correct sitting after SCI. In addition to these passive devices, functional electrical stimulation (FES) could be used to artificially contract trunk muscles and regulate sitting balance. The objectives of this research project were to: (1) investigate neuromuscular synergies of the trunk during perturbed sitting; (2) investigate the effects of anticipation of the perturbation on trunk muscle responses; (3) compare sitting balance between able-bodied individuals and people with SCI; and (4) examine the effects of electrical stimulation of trunk muscles on sitting balance. The first deliverable (Chapter 2) of this project was the development of neural network models that encode trunk muscle responses during perturbed quiet sitting. These models describe complex neuromuscular synergies of the trunk and allow us to understand which muscles are used to stabilize sitting balance. The second deliverable (Chapter 3) was a study which showed that anticipation of direction and time of perturbation resulted in approximately 15 ms faster trunk muscle activations. These results indicate that the reflexive and patterned neuromuscular responses of the trunk can be modulated by the central nervous system using anticipatory information. The third deliverable (Chapter 4) was a study that investigated differences in sitting balance between able-bodied individuals and individuals with SCI. This study has shown that trunk control is significantly compromised in individuals with SCI, which is the main cause of their reduced balance control during quiet sitting. The fourth deliverable (Chapter 5) was a study that investigated the effects of FES of trunk muscle on sitting balance control. The results showed that co-contractions of trunk muscles with FES could increase trunk stiffness. These findings combined advanced our understanding of the neuromuscular control of the trunk during sitting balance. Moreover, they helped us develop a neuroprosthesis, which could improve sitting balance in individuals with SCI, and consequently contribute to improving their mobility, independence and, ultimately, quality of life.Ph.D

Contractile properties of superficial skeletal muscle affect postural control in healthy young adults: A test of the rambling and trembling hypothesis.

The rambling and trembling analysis separates the center of pressure (COP) fluctuations into two components: rambling (supraspinal contribution) and trembling (muscle stiffness / reflexive properties contribution). We examined whether the trembling component is correlated to the contractile properties (muscle stiffness and contraction time) of lower limb superficial skeletal muscles to experimentally test the rambling and trembling hypothesis. We hypothesized that muscle stiffness and contraction time, would be: (a) more correlated with; and (b) have a greater impact on the trembling component compared to the rambling component. Thirty-two healthy young adults were recruited for the study and tensiomyography was used to assess mechanical muscle responses to a single electrical stimulus to calculate muscle stiffness and contraction time based on radial muscle belly displacement measurements of lower limb muscles unilaterally. Moreover, upright postural control was assessed using a force plate to record ground reaction forces and moments and calculate the COP fluctuations during two 30 seconds trials. From the COP fluctuations, rambling and trembling time series were extracted, and all fluctuation time series were described using a number of different time-domain and frequency-domain parameters in both the anterior-posterior and medial-lateral directions. Our results demonstrated that both muscle stiffness and contraction time were moderately correlated with time-domain and frequency-domain parameters of the trembling component, as compared with those of the rambling component which was not as well correlated. Moreover, they also predicted the trembling component better. Overall, these results imply that postural control during quiet stance is, in part, related to intrinsic muscle stiffness in the lower extremities. Moreover, we showed that the rambling and trembling hypothesis is effective in separating postural sway fluctuations during upright posture to extract the contributions of muscle stiffness / reflexive properties (trembling), and likely the supraspinal contribution (rambling)

Trunk muscle co-activation using functional electrical stimulation modifies center of pressure fluctuations during quiet sitting by increasing trunk stiffness

Abstract Background The purpose of this study was to examine the impact of functional electrical stimulation (FES) induced co-activation of trunk muscles during quiet sitting. We hypothesized that FES applied to the trunk muscles will increase trunk stiffness. The objectives of this study were to: 1) compare the center of pressure (COP) fluctuations during unsupported and FES-assisted quiet sitting - an experimental study and; 2) investigate how FES influences sitting balance - an analytical (simulation) study. Methods The experimental study involved 15 able-bodied individuals who were seated on an instrumented chair. During the experiment, COP of the body projected on the seating surface was calculated to compare sitting stability of participants during unsupported and FES-assisted quiet sitting. The analytical (simulation) study examined dynamics of quiet sitting using an inverted pendulum model, representing the body, and a proportional-derivative (PD) controller, representing the central nervous system control. This model was used to analyze the relationship between increased trunk stiffness and COP fluctuations. Results In the experimental study, the COP fluctuations showed that: i) the mean velocity, mean frequency and the power frequency were higher during FES-assisted sitting; ii) the frequency dispersion for anterior-posterior fluctuations was smaller during FES-assisted sitting; and iii) the mean distance, range and centroidal frequency did not change during FES-assisted sitting. The analytical (simulation) study showed that increased mechanical stiffness of the trunk had the same effect on COP fluctuations as the FES. Conclusions The results of this study suggest that FES applied to the key trunk muscles increases the speed of the COP fluctuations by increasing the trunk stiffness during quiet sitting

Why brain-controlled neuroprosthetics matter: mechanisms underlying electrical stimulation of muscles and nerves in rehabilitation

Abstract Delivering short trains of electric pulses to the muscles and nerves can elicit action potentials resulting in muscle contractions. When the stimulations are sequenced to generate functional movements, such as grasping or walking, the application is referred to as functional electrical stimulation (FES). Implications of the motor and sensory recruitment of muscles using FES go beyond simple contraction of muscles. Evidence suggests that FES can induce short- and long-term neurophysiological changes in the central nervous system by varying the stimulation parameters and delivery methods. By taking advantage of this, FES has been used to restore voluntary movement in individuals with neurological injuries with a technique called FES therapy (FEST). However, long-lasting cortical re-organization (neuroplasticity) depends on the ability to synchronize the descending (voluntary) commands and the successful execution of the intended task using a FES. Brain-computer interface (BCI) technologies offer a way to synchronize cortical commands and movements generated by FES, which can be advantageous for inducing neuroplasticity. Therefore, the aim of this review paper is to discuss the neurophysiological mechanisms of electrical stimulation of muscles and nerves and how BCI-controlled FES can be used in rehabilitation to improve motor function

TRIBUTE: Dejan B. Popović (1950–2021)

Dr. Dejan B. Popović passed away on October 4, 2021, in Belgrade, Serbia. At the funeral, on October 8, he was accompanied by his favorite song by Frank Sinatra, “My way,” which perfectly described his life. He was a retired professor of Biomedical Engineering at the Faculty of Electrical Engineering, University of Belgrade, Serbia, a full member of the Serbian Academy of Sciences and Arts, an Emeritus professor of Rehabilitation Engineering at Aalborg University in Denmark, and an Associate Member of the Slovenian Academy of Sciences and Arts