Doctor of Philosophy

dissertationIntegration of sensory inputs by the central nervous system (CNS) is necessary for adequate postural stability, but diminishes with age and is further impaired in Parkinson disease (PD). As a result, the CNS cannot appropriately weight sensory stimuli to facilitate postural responses to sudden changes in sensory input. Training the sensorimotor system to ignore or rapidly adapt to aberrant postural cues may improve postural control in PD. We evaluated the influence of acute and repeated exposure to galvanic vestibular stimulation (GVS) on postural responses during static and dynamic tasks to determine whether training improved these responses. We hypothesized that individuals with PD would demonstrate impaired postural recovery responses to acute GVS relative to healthy controls and that individuals with PD and healthy elders would demonstrate diminished adaptive responses to repeated GVS compared to young adults. Twelve individuals with PD (PD group), 15 healthy young adults (HY group), and 11 healthy elders (HE group) participated. Timing of GVS was randomly applied during each task. Fifteen acquisition and nine retention trials with GVS were compared to assess learning. The PD group took longer to stabilize their center of pressure (COP) in quiet stance following GVS acutely compared to controls. The PD and HE groups had lower sample entropy (SaEn) compared to the HY. Neither the PD nor HE groups demonstrated changes in SaEn or meaningful improvements in postural control during acquisition or retention. SaEn in the HY group acutely decreased and then increased at retention which coincided with a meaningful improvement in postural control. The PD group had impaired motor planning, postural preparation, and postural stability during a rise to toes task following acute GVS, but these constructs returned to baseline at later acquisition and retention time points. Controls suppressed GVS acutely Postural coordination decreased acutely in the PD group during tether release. This persisted and an adaptive trend in BOS transition was noted with repeated GVS exposure in this group. No changes were observed in the control groups. Taken together, these results demonstrated that acute GVS differentially affects postural control in individuals with PD. Our results support the hypothesis that reweighting of sensory stimuli is impaired in PD. We also show that individuals with PD are able to suppress attention to a vestibular illusion and demonstrate adaptive responses to a postural threat

The Influence of Plantar Cutaneous Stimulation on a Functional Test of Gait in Parkinson’s Disease

Although possible deficits in proprioception have been implicated as a cause of gait impairments in individuals with Parkinson’s disease (PD), little research has been done to investigate improving this possible deficit as a method to influence mobility. The overall purpose of the current thesis was to investigate the influence of increased plantar stimulation on stability and gait impairments. This study also investigated the contribution of attention to locomotion in PD. The two studies comprising this thesis addressed the possible influence of the ribbed insoles in the initial response of PD participants as well as the long-term use of the insole. The first study focused on developing a task to assess the influence of the facilitatory insoles on gait for individuals with PD compared to healthy control participants. For the purpose of evaluating the facilitatory insoles in a functionally relevant task participants performed a modified “Timed Up and Go” task with an additional secondary motor task. The secondary task of carrying a tray with glasses demonstrated that attention plays a large role in the production and maintenance of gait as gait deficits became more pronounced. However, the facilitatory insoles also influenced gait parameters which demonstrated that the possible deficits in proprioception contribute to the gait impairments in PD. The initial response to the insoles, in the first study, did not improve gait parameters, which suggests that PD participants may need more time to adjust to the increased plantar stimulation. The second study investigated the influence of the facilitatory insoles when they are worn for a longer period of time. Participants wore either the facilitatory insoles or blank insoles while completing the PD Sensory Attention Focussed Exercise (PD SAFEx) rehabilitation program. Results demonstrated that when the facilitatory insoles are worn long-term, they can benefit the turning and straight-line walking in individuals with PD. PD participants became more confident in their ability to turn as they exerted less control over their centre of mass. Participants also displayed a decreased base of support and time spent in double limb support without negatively affecting lateral stability. These improvements suggest that the facilitatory insoles, when worn long-term, allow for a more normalized pattern of gait for individuals with PD. The TUG task used in this thesis proved to be a good measure to evaluate changes in stability and gait parameters in PD participants. Long-term use of the facilitatory insoles demonstrated improvements in stability and gait deficits during difficult aspects of gait such as turning. This suggests that the facilitatory insoles would be a simple and effective intervention to use, however further investigation should occur to ensure that the improvements will continue when facilitatory insoles are used on a daily basis. As well, investigation into the long-term use of other types of cutaneous stimulation such as vibratory insoles would be beneficial for the PD population

Emotional, cognitive, and postural adaptations to repeated postural threat exposure

This thesis investigated initial threat-induced changes in emotional, cognitive, and postural control measures and adaptation of these measures to repeated threat exposure in healthy young and older adults. Twenty-seven young and twenty-seven older adults stood on a platform under no threat and threat conditions. Postural threat was manipulated by altering the expectation of a temporally and directionally unpredictable mediolateral support surface translation during quiet standing. Regardless of age, participants were more anxious, reported broad changes in attention focus, and increased centre of pressure (COP) amplitude and frequency with first threat exposure. With early threat exposure, participants were less anxious and increased COP frequency. With repeated threat exposure, participants were less anxious, reported reductions in threat-induced changes in attention focus, and decreased high frequency COP displacements. These results suggest young and older adults demonstrate similar patterns of emotional, cognitive, and postural adaptations to initial and repeated threat exposure

The Effects of Dance Therapy on Voice in Patients with Parkinson\u27s Disease in a Multicultural Population

Current literature suggests that dance therapy in individuals with Parkinson’s disease shows noticeable improvement in motor functions, for example gait and balance improvement. Additionally, patients with Parkinson’s disease who participate in dance therapy may perceive positive benefits on their quality of life. Therefore, it is believed that increases in core support and improvements in posture, as a result of dance therapy, will have effects on the voice in patients with PD. This thesis pulls from literature supporting treatment approaches in the field of speech-language pathology for voice patients with Parkinson’s disease. The aim of this study was to evaluate the benefits of dance therapy on voice in patients with Parkinson’s disease in a multicultural population. In this study, a quantitative design was employed to record patients’ perceptions of effects on their voice following dance therapy. Research findings reveal half of respondents observed improvements in their voice following dance therapy

Rôle des informations proprioceptives dans l’équilibre à la marche chez les personnes en santé et hémiparétiques

L'utilisation des informations proprioceptives pour le contrôle de l’équilibre à la marche est encore mal comprise chez les sujets en santé ou hémiparétiques suite à un accident vasculaire cérébral. Le but de cette étude était d’évaluer le rôle des informations proprioceptives dans le maintien de l'équilibre à la marche chez les patients en santé et hémiparétiques. Une analyse de mouvement en trois dimensions a été faite chez treize participants en santé et six hémiparétiques qui marchaient sur un tapis roulant instrumenté pour déterminer leur difficulté à maintenir l’équilibre postural et dynamique, évaluée respectivement par les forces stabilisante et déstabilisante. Des vibrations étaient appliquées en continu ou pendant la phase d’appui sur les muscles postérieurs du cou et sur le triceps sural du côté non-dominant/parétique. La vibration continue ou à l’appui du triceps sural a diminué, chez les sujets en santé, la difficulté à maintenir l’équilibre dynamique et postural (p.17). Aucun effet des vibrations n'a été mesuré chez les patients hémiparétiques (p> 0,45). Les informations proprioceptives sont donc bien utilisées lors de la marche, mais leur rôle dépendrait des conditions de marche et des afférences visuelles disponibles. Un changement dans les capacités d’intégration expliquerait l'absence d'effet des vibrations chez les patients hémiparétiques. D’autres études sont nécessaires pour comprendre l’intégration des informations proprioceptives et visuelles dans le contrôle de l’équilibre à la marche.Proprioceptive information is important for balance control, but little is known about how it is used during gait, or how stroke affects this use. The aim of this study was to evaluate the role of neck and ankle proprioception in balance during gait in healthy participants and after stroke. Thirteen healthy and 6 hemiparetic participants walked on an instrumented treadmill in a fully lit room, while whole-body three-dimension kinematics was quantified. Vibration was applied on the posterior neck muscles and triceps surae tendon on the non-dominant/paretic side, continuously or during the stance phase only. Difficulty to maintain dynamic and postural balance was evaluated using the stabilizing and destabilizing forces, respectively. Summary data of gait kinematics and kinetics were also reported. Continuous and stance phase vibration of the triceps surae decreased, in healthy patients, the difficulty to maintain both dynamic and postural balance in healthy participants (p.17). None of the vibration conditions affected balance or gait parameters in stroke participants. The results confirmed that proprioception information is used for control balance during gait. Its importance depends on the walking and visual conditions. Changes in sensory integration capacities likely explain the results after stroke. Further study is needed to understand the integration of proprioception and vision information to control balance during gait

The Role of the Central Nervous System in the Integration of Proprioceptive Information

The proprioceptive system provides feedback on human performance that makes it possible to learn and perform novel tasks. Proprioception predominately arises in the peripheral nervous system at the muscle spindle organ. Mechanical stimulus such as vibration has been implicated in altering muscle spindle afferent signals used as feedback. Researchers have utilized this understanding to document gross performance changes resulting from a muscle spindle disruption paradigm. Findings of this work have demonstrated that the altered proprioceptive feedback alters performance both during and after vibration exposure. This has also led many to postulate that altered proprioceptive feedback due to environmental working conditions may be responsible for many incidences of musculoskeletal injury, including low back pain. In order to more fully understand how proprioceptive feedback is integrated into a motor response it was required to investigate activity within the central nervous system, itself the target of the spindle afferent, both before and after receiving a modulate afferent. We developed a protocol based on measures of average velocity to test for this activity. Our investigation began we examining whether or not average velocity, in the form of seated sway velocity, would be sensitive to applied vibration. We found that while vibration was applied; mean sway speed increased significantly above pre vibration levels, regardless of feedback and task difficulty. A computer based pursuit task was then implemented in order to investigate performance relative to timing of vibration exposure. Our results revealed a significant decrease in pursuit velocity during vibration from pre-vibration velocity. Additionally, subjects demonstrated an equal magnitude but opposite increase in pursuit speed after vibration was removed. This protocol was then replicated in a functional-MRI to compare the gross motor pursuit task performance with the corresponding BOLD imaging data. We observed a similar decrease/increase pattern of joystick pursuit velocity. The corresponding cortical activity revealed patterns of inhibition consistent with cognitive inhibition. The current findings support proprioception as a central inhibitory control mechanism that shifts cortical networks dependent on available sensory stimulus

Evaluating Two Measures of Postural Stability in Response to Perturbations in People with Diabetic Neuropathy

Diabetic neuropathy is a common complication of diabetes. It is characterized by a marked decrease in proprioception, particularly in the lower body. This reduced proprioception leads to an increase in falls risk in this population. The purposes of this study were to compare two measures of postural stability, sway excursion and virtual time-to-contact, with disease severity in persons with diabetic neuropathy in response to anteroposterior and mediolateral support-surface perturbations and to identify the relationship between virtual time-to-contact and disease severity in persons with diabetic neuropathy in response to oblique support-surface perturbations. We hypothesized that virtual time-to-contact would provide a more sensitive and robust measure of postural stability for people with diabetic neuropathy in response to anteroposterior and mediolateral perturbations. We also hypothesized that as disease severity increased, postural stability would decrease in response to oblique perturbations. We expected a direct relationship between disease severity and sway excursion and an inverse relationship between disease severity and virtual time-to-contact.   Postural kinematics and force plate data were collected for ten adults with diabetes and a range of neuropathy from none to moderate-severe. Postural kinematics were collected using an eight-camera Qualisys motion capture system. Perturbations were controlled by and force plate data was collected using a NeuroCom Research Module. Each participant was perturbed in eight directions, at two speeds per direction (10 cm/sec and 20 cm/sec), and for two trials for each condition for a total of thirty two perturbations. Nine statistically significant correlations were found between disease severity and virtual time-to-contact, while one statistically significant correlation was found between disease severity and sway excursion. Interestingly, the nine correlations between disease severity and virtual time-to-contact were all positive correlations.   We had support for our first hypothesis in that virtual time-to-contact had more correlations with disease severity than sway excursion across anteroposterior and mediolateral perturbations at both perturbation speeds. Our second hypothesis was not supported, in that virtual time-to-contact increased in response to oblique perturbations as disease severity increased. On average, virtual time-to-contact can explain 58% of the variation in disease severity. Further research is needed into why virtual time-to-contact was unexpectedly directly correlated with disease severity of diabetic neuropathy.  M.S

Rehabilitation Engineering in Parkinson's disease

Impairment of postural control is a common consequence of Parkinson's disease (PD) that becomes more and more critical with the progression of the disease, in spite of the available medications. Postural instability is one of the most disabling features of PD and induces difficulties with postural transitions, initiation of movements, gait disorders, inability to live independently at home, and is the major cause of falls. Falls are frequent (with over 38% falling each year) and may induce adverse consequences like soft tissue injuries, hip fractures, and immobility due to fear of falling. As the disease progresses, both postural instability and fear of falling worsen, which leads patients with PD to become increasingly immobilized. The main aims of this dissertation are to: 1) detect and assess, in a quantitative way, impairments of postural control in PD subjects, investigate the central mechanisms that control such motor performance, and how these mechanism are affected by levodopa; 2) develop and validate a protocol, using wearable inertial sensors, to measure postural sway and postural transitions prior to step initiation; 3) find quantitative measures sensitive to impairments of postural control in early stages of PD and quantitative biomarkers of disease progression; and 4) test the feasibility and effects of a recently-developed audio-biofeedback system in maintaining balance in subjects with PD. In the first set of studies, we showed how PD reduces functional limits of stability as well as the magnitude and velocity of postural preparation during voluntary, forward and backward leaning while standing. Levodopa improves the limits of stability but not the postural strategies used to achieve the leaning. Further, we found a strong relationship between backward voluntary limits of stability and size of automatic postural response to backward perturbations in control subjects and in PD subjects ON medication. Such relation might suggest that the central nervous system presets postural response parameters based on perceived maximum limits and this presetting is absent in PD patients OFF medication but restored with levodopa replacement. Furthermore, we investigated how the size of preparatory postural adjustments (APAs) prior to step initiation depend on initial stance width. We found that patients with PD did not scale up the size of their APA with stance width as much as control subjects so they had much more difficulty initiating a step from a wide stance than from a narrow stance. This results supports the hypothesis that subjects with PD maintain a narrow stance as a compensation for their inability to sufficiently increase the size of their lateral APA to allow speedy step initiation in wide stance. In the second set of studies, we demonstrated that it is possible to use wearable accelerometers to quantify postural performance during quiet stance and step initiation balance tasks in healthy subjects. We used a model to predict center of pressure displacements associated with accelerations at the upper and lower back and thigh. This approach allows the measurement of balance control without the use of a force platform outside the laboratory environment. We used wearable accelerometers on a population of early, untreated PD patients, and found that postural control in stance and postural preparation prior to a step are impaired early in the disease when the typical balance and gait intiation symptoms are not yet clearly manifested. These novel results suggest that technological measures of postural control can be more sensitive than clinical measures. Furthermore, we assessed spontaneous sway and step initiation longitudinally across 1 year in patients with early, untreated PD. We found that changes in trunk sway, and especially movement smoothness, measured as Jerk, could be used as an objective measure of PD and its progression. In the third set of studies, we studied the feasibility of adapting an existing audio-biofeedback device to improve balance control in patients with PD. Preliminary results showed that PD subjects found the system easy-to-use and helpful, and they were able to correctly follow the audio information when available. Audiobiofeedback improved the properties of trunk sway during quiet stance. Our results have many implications for i) the understanding the central mechanisms that control postural motor performance, and how these mechanisms are affected by levodopa; ii) the design of innovative protocols for measuring and remote monitoring of motor performance in the elderly or subjects with PD; and iii) the development of technologies for improving balance, mobility, and consequently quality of life in patients with balance disorders, such as PD patients with augmented biofeedback paradigms

Effets de la vibration des muscles sur les mécanismes neuronaux et la fonction du membre supérieur et inférieur des personnes ayant une hémiparésie chronique

Cette thèse vise à répondre à trois questions fondamentales: 1) La diminution de l’excitabilité corticospinale et le manque d’inhibition intracorticale observés suite à la stimulation magnétique transcrânienne (SMT) du cortex moteur de la main atteinte de sujets hémiparétiques sont-ils aussi présents suite à la SMT du cortex moteur de la jambe atteinte? 2) Est-ce que les altérations dans l’excitabilité corticomotrice sont corrélées aux déficits et incapacités motrices des personnes ayant subi un accident vasculaire cérébral depuis plus de 6 mois? 3) La vibration musculaire, étant la source d’une forte afférence sensorielle, peut-elle moduler l’excitabilité corticomotrice et améliorer la performance motrice de ces personnes? Premièrement, afin d’appuyer notre choix d’intervention et d’évaluer le potentiel de la vibration mécanique locale pour favoriser la réadaptation des personnes ayant une atteinte neurologique, nous avons réalisé une révision en profondeur de ses applications et intérêts cliniques à partir d’informations trouvées dans la littérature scientifique (article 1). La quantité importante d’information sur les effets physiologiques de la vibration contraste avec la pauvreté des études qui ont évalué son effet thérapeutique. Nous avons trouvé que, malgré le manque d’études, les résultats sur son utilisation sont encourageants et positifs et aucun effet adverse n’a été rapporté. Dans les trois autres articles qui composent cette thèse, l’excitabilité des circuits corticospinaux et intracorticaux a été étudiée chez 27 sujets hémiparétiques et 20 sujets sains sans atteintes neurologiques. Les fonctions sensorimotrices ont aussi été évaluées par des tests cliniques valides et fidèles. Tel qu’observé à la main chez les sujets hémiparétiques, nous avons trouvé, par rapport aux sujets sains, une diminution de l’excitabilité corticospinale ainsi qu’un manque d’inhibition intracorticale suite à la SMT du cortex moteur de la jambe atteinte (article 2). Les sujets hémiparétiques ont également montré un manque de focus de la commande motrice lors de l’activation volontaire des fléchisseurs plantaires. Ceci était caractérisé par une augmentation de l’excitabilité nerveuse des muscles agonistes, mais aussi généralisée aux synergistes et même aux antagonistes. De plus, ces altérations ont été corrélées aux déficits moteurs au membre parétique. Le but principal de cette thèse était de tester les effets potentiels de la vibration des muscles de la main (article 3) et de la cuisse (article 4) sur les mécanismes neuronaux qui contrôlent ces muscles. Nous avons trouvé que la vibration augmente l’amplitude de la réponse motrice des muscles vibrés, même chez des personnes n’ayant pas de réponse motrice au repos ou lors d’une contraction volontaire. La vibration a également diminué l’inhibition intracorticale enregistrée au quadriceps parétique (muscle vibré). La diminution n’a cependant pas été significative au niveau de la main. Finalement, lors d’un devis d’investigation croisé, la vibration de la main ou de la jambe parétique a résulté en une amélioration spécifique de la dextérité manuelle ou de la coordination de la jambe, respectivement. Au membre inférieur, la vibration du quadriceps a également diminuée la spasticité des patients. Les résultats obtenus dans cette thèse sont très prometteurs pour la rééducation de la personne hémiparétique car avec une seule séance de vibration, nous avons obtenu des améliorations neurophysiologiques et cliniques.This thesis aims to answer three basic questions: 1) Are the decrease in corticospinal excitability and the lack of intracortical inhibition observed following transcranial magnetic stimulation (TMS) of the affected hand motor cortex of stroke patients present after TMS of the affected leg motor cortex? 2) Are the alterations in corticomotor excitability correlated with motor impairments and disabilities of subjects who have suffered a stroke for over six months? 3) Can muscle vibration, as a source of strong sensory afference modulate corticomotor excitability and improve motor performance of these subjects? First of all, to support our choice of intervention and to assess the potential of local mechanical vibration to promote the recovery of persons with neurological impairment, we conducted a thorough review of its physiological effects and clinical applications in the scientific literature (article 1). The wealth of information on the physiological effects of vibration contrasts with the lack of studies that have evaluated its therapeutic effects. Nevertheless, we found that, despite the paucity of studies, the results on its clinical use are encouraging and positive and no adverse effects were reported. In the other three articles included in this thesis, the excitability of corticospinal and intracortical circuits has been studied in 27 hemiparetic patients and in 20 healthy subjects without neurological disease or injury. Sensorimotor functions were also evaluated with valid and reliable clinical tests. Similar to that observed in the hand of hemiparetic patients, we found, compared to the healthy subjects, a decrease of corticospinal excitability and a lack of intracortical inhibition following TMS of the affected leg motor cortex (Article 2). The hemiparetic patients also showed a lack of focus of the motor output during voluntary activation of plantar flexors. This was characterized by an increase in the neural excitability not only of the agonist muscles, but also of the synergists and even the antagonist muscles. The main goal of this thesis was to test the potential effects of vibrating hand (Article 3) and thigh (Article 4) muscles on the neural mechanisms that control these muscles. We found that vibration increases the amplitude of motor responses in the vibrated muscles and even produces a response in subjects with no motor response at rest or during a voluntary contraction. The vibration also decreased the intracortical inhibition recorded in the paretic quadriceps muscle (vibrated muscle). The decrease was however not significant at the hand. Finally, using a cross-over design study, the vibration of the paretic hand or leg resulted in specific improvements in hand dexterity or leg coordination, respectively. In the lower limb, quadriceps vibration also reduced the spasticity in patients. The results obtained in this thesis are very promising for stroke rehabilitation because with a single session of vibration, we obtained neurophysiological and clinical improvements

Exploring the effects of spinal cord stimulation for freezing of gait in parkinsonian patients

Dopaminergic replacement therapies (e.g. levodopa) provide limited to no response for axial motor symptoms including gait dysfunction and freezing of gait (FOG) in Parkinson’s disease (PD) and Richardson’s syndrome progressive supranuclear palsy (PSP-RS) patients. Dopaminergic-resistant FOG may be a sensorimotor processing issue that does not involve basal ganglia (nigrostriatal) impairment. Recent studies suggest that spinal cord stimulation (SCS) has positive yet variable effects for dopaminergic-resistant gait and FOG in parkinsonian patients. Further studies investigating the mechanism of SCS, optimal stimulation parameters, and longevity of effects for alleviating FOG are warranted. The hypothesis of the research described in this thesis is that mid-thoracic, dorsal SCS effectively reduces FOG by modulating the sensory processing system in gait and may have a dopaminergic effect in individuals with FOG. The primary objective was to understand the relationship between FOG reduction, improvements in upper limb visual-motor performance, modulation of cortical activity and striatal dopaminergic innervation in 7 PD participants. FOG reduction was associated with changes in upper limb reaction time, speed and accuracy measured using robotic target reaching choice tasks. Modulation of resting-state, sensorimotor cortical activity, recorded using electroencephalography, was significantly associated with FOG reduction while participants were OFF-levodopa. Thus, SCS may alleviate FOG by modulating cortical activity associated with motor planning and sensory perception. Changes to striatal dopaminergic innervation, measured using a dopamine transporter marker, were associated with visual-motor performance improvements. Axial and appendicular motor features may be mediated by non-dopaminergic and dopaminergic pathways, respectively. The secondary objective was to demonstrate the short- and long-term effects of SCS for alleviating dopaminergic-resistant FOG and gait dysfunction in 5 PD and 3 PSP-RS participants without back/leg pain. SCS programming was individualized based on which setting best improved gait and/or FOG responses per participant using objective gait analysis. Significant improvements in stride velocity, step length and reduced FOG frequency were observed in all PD participants with up to 3-years of SCS. Similar gait and FOG improvements were observed in all PSP-RS participants up to 6-months. SCS is a promising therapeutic option for parkinsonian patients with FOG by possibly influencing cortical and subcortical structures involved in locomotion physiology