Effects of Sensorimotor Perturbations on Balance Performance and Electrocortical Dynamics

Humans must frequently adapt their posture to prevent loss of balance. Such balance control requires complex, precisely-timed coordination among sensory input, neural processing, and motor output. Despite its importance, our current understanding of cortical involvement during balance control remains limited by traditional neuroimaging methods, which are stationary and have poor time resolution. High-density electroencephalography (EEG), combined with independent component analysis, has become a promising tool for recording cortical dynamics during balance perturbations due to its portability and high temporal resolution. Additionally, recent improvements in immersive virtual reality headsets may provide new rehabilitative paradigms, but the effects of virtual reality on balance and cortical function remain poorly understood. In my first study, I recorded high-density EEG from healthy, young adult subjects as they walked along a beam with and without virtual reality high heights exposure. While virtual high heights did induce stress, the use of virtual reality during the task increased performance errors and EEG measures of cognitive loading compared to real-world viewing without a headset. In my second study, I collected high-density EEG from healthy young adults as they walked along a treadmill-mounted balance beam to determine the effect of a transient visual perturbation on training in virtual reality. Subjects in the perturbations group improved comparably to those that trained without virtual reality, indicating that the perturbation helped subjects overcome the negative effects of virtual reality on motor learning. The perturbation primarily elicited a cognitive change. In my third study, healthy, young adult EEG was recorded during physical pull and visual rotation perturbations to tandem walking and tandem standing. I found similar electrocortical patterns for both perturbation types, but different cortical areas were involved for each. In my fourth study, I used a phantom head to validate EEG connectivity methods based on Granger causality in a real-world environment. In general, connectivity measures could determine the underlying connections, but many were susceptible to high-frequency false positives. Using data from my third study, my fifth study analyzed corticomuscular connectivity patterns following sensorimotor balance perturbations. I found strong occipito-parietal connections regardless of perturbation type, along with evidence of direct muscular control from the supplementary motor area during the standing perturbation response. Taken together, the work presented in this dissertation greatly expands upon the current knowledge of cortical processing during sensorimotor balance perturbations and the effect of such perturbations on short-term motor learning, providing multiple avenues for future exploration.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147615/1/stepeter_1.pd

VR systems for memory assessment and depth perception

La evolución de la tecnología de Realidad Virtual (RV) ha contribuido en todos los campos, incluyendo la psicología. Esta evolución implica mejoras tanto en hardware como en software, que permiten experiencias más inmersivas. En un entorno de RV los usuarios pueden percibir la sensación de "presencia" y sentirse "inmersos". Estas sensaciones son posibles utilizando HMDs. Hoy en día, el desarrollo de los HMDs se ha centrado en mejorar sus características técnicas para ofrecer inmersión total. En psicología, los entornos de RV son una herramienta de investigación. Hay algunas aplicaciones para evaluar la memoria espacial que utilizan métodos básicos de interacción. Sin embargo, sistemas de RV que incorporen estereoscopía y movimiento físico todavía no se han explotado en psicología. En esta tesis, se ha desarrollado un nuevo sistema de RV que combina características inmersivas, interactivas y de movimiento. El sistema de RV (tarea en un laberinto virtual) se ha utilizado para evaluar la memoria espacial y la percepción de profundidad. Se han integrado dos tipos diferentes de interacción: una basada en locomoción que consistió en pedalear en una bicicleta fija (condición1) y otra estacionaria usando un gamepad (condición2). El sistema integró dos tipos de visualización: 1) Oculus Rift (OR); 2) Una gran pantalla estéreo. Se diseñaron dos estudios. El primer estudio (N=89) evaluó la memoria espacial a corto plazo usando el OR y los dos tipos de interacción. Los resultados indican que existían diferencias significativas entre ambas condiciones. Los participantes que utilizaron la condición2 obtuvieron mejor rendimiento que los que utilizaron la tarea en la condición1. Sin embargo, no se encontraron diferencias significativas en las puntuaciones de satisfacción e interacción entre ambas condiciones. El desempeño en la tarea correlacionó con el desempeño en las pruebas neuropsicológicas clásicas, revelando la verosimilitud entre ellas. El segundo estudio (N=59) incluyó participantes con y sin estereopsis. Este estudio evaluó la percepción de profundidad comparando los dos sistemas de visualización. Los participantes realizaron la tarea usando la condición2. Los resultados mostraron que las diferentes características del sistema de visualización no influyeron en el rendimiento en la tarea entre los participantes con y sin estereopsis. Se encontraron diferencias significativas a favor del HMD entre las dos condiciones y entre los dos grupos de participantes respecto a la percepción de profundidad. Los participantes que no tenían estereopsis y no podían percibir la profundidad cuando utilizaban otros sistemas de visualización, tuvieron la ilusión de percepción de profundidad cuando utilizaron el OR. El estudio sugiere que para las personas que no tienen estereopsis, el seguimiento de la cabeza influye en gran medida en la experiencia 3D. Los resultados estadísticos de ambos estudios han demostrado que el sistema de RV desarrollado es una herramienta apropiada para evaluar la memoria espacial a corto plazo y la percepción de profundidad. Por lo tanto, los sistemas de RV que combinan inmersión total, interacción y movimiento pueden ser una herramienta útil para la evaluación de procesos cognitivos humanos como la memoria. De estos estudios se han extraído las siguientes conclusiones generales: 1) La tecnología de RV y la inmersión proporcionada por los actuales HMDs son herramientas adecuadas para aplicaciones psicológicas, en particular, la evaluación de la memoria espacial a corto plazo; 2) Un sistema de RV como el presentado podría ser utilizado como herramienta para evaluar o entrenar adultos en habilidades relacionadas con la memoria espacial a corto plazo; 3) Los dos tipos de interacción utilizados para la navegación en el laberinto virtual podrían ser útiles para su uso con diferentes colectivos; 4) El OR permite que los usuarios sin estereopsis puedan percibir lThe evolution of Virtual Reality (VR) technology has contributed in all fields, including psychology. This evolution involves improvements in hardware and software allowing more immersive experiences. In a VR environment users can perceive the sensation of "presence" and feel "immersed". These sensations are possible using VR devices as HMDs. Nowadays, the development of the HMDs has focused on improving their technical features to offer full immersion. In psychology, VR environments are research tools because they allow the use of new paradigms that are not possible to employ in a real environment. There are some applications for assessing spatial memory that use basic methods of HCI. However, VR systems that incorporate stereoscopy and physical movement have not yet been exploited in psychology. In this thesis, a novel VR system combining immersive, interactive and motion features was developed. This system was used for the assessment of the spatial memory and the evaluation of depth perception. For this system, a virtual maze task was designed and implemented. In this system, two different types of interaction were integrated: a locomotion-based interaction pedaling a fixed bicycle (condition1), and a stationary interaction using a gamepad (condition2). This system integrated two types of display systems: 1) The Oculus Rift; 2) A large stereo screen. Two studies were designed to determine the efficacy of the VR system using physical movement and immersion. The first study (N=89) assessed the spatial short term memory using the Oculus Rift and the two types of interaction The results showed that there were statistically significant differences between both conditions. The participants who performed the condition2 got better performance than participants who performed the condition1. However, there were no statistically significant differences in satisfaction and interaction scores between both conditions. The performance on the task correlated with the performance on other classical neuropsychological tests, revealing a verisimilitude between them. The second study (N=59) involved participants who had and who had not stereopsis. This study assessed the depth perception by comparing the two display systems. The participants performed the task using the condition2. The results showed that the different features of the display system did not influence the performance on the task between the participants with and without stereopsis. Statistically significant differences were found in favor of the HMD between the two conditions and between the two groups of participants regard to depth perception. The participants who did not have stereopsis and could not perceive the depth when they used other display systems (e.g. CAVE); however, they had the illusion of depth perception when they used the Oculus Rift. The study suggests that for the people who did not have stereopsis, the head tracking largely influences the 3D experience. The statistical results of both studies have proven that the VR system developed for this research is an appropriate tool to assess the spatial short-term memory and the depth perception. Therefore, the VR systems that combine full immersion, interaction and movement can be a helpful tool for the assessment of human cognitive processes as the memory. General conclusions from these studies are: 1) The VR technology and immersion provided by current HMDs are appropriate tools for psychological applications, in particular, the assessment of spatial short-term memory; 2) A VR system like the one presented in this thesis could be used as a tool to assess or train adults in skills related to spatial short-term memory; 3) The two types of interaction (condition1 and condition2) used for navigation within the virtual maze could be helpful to use with different collectives; 4) The Oculus Rift allows that the users without stereopsis can perceive the depth perception of 3D objects and have rich 3D experiences.L'evolució de la tecnologia de Realitat Virtual (RV) ha contribuït en tots els camps, incloent la psicologia. Aquesta evolució implica millores en el maquinari i el programari que permeten experiències més immersives. En un entorn de RV, els usuaris poden percebre la sensació de "presència" i sentir-se "immersos". Aquestes sensacions són possibles utilitzant HMDs. Avui dia, el desenvolupament dels HMDs s'ha centrat a millorar les seves característiques tècniques per oferir immersió plena. En la psicologia, els entorns de RV són eines de recerca. Hi ha algunes aplicacions per avaluar la memòria espacial que utilitzen mètodes bàsics d'interacció. Tanmateix, sistemes de RV que incorporen estereoscòpia i moviment físic no s'han explotat en psicologia. En aquesta tesi, s'ha desenvolupat un sistema de RV novell que combina immersió, interacció i moviment. El sistema (tasca en un laberint virtual) s'ha utilitzat per a l'avaluació de la memòria espacial i la percepció de profunditat. S'han integrat dos tipus d'interacció: una interacció basada en locomoció pedalejant una bicicleta fixa (condició1), i l'altra una interacció estacionària usant un gamepad (condició2). S'han integrat dos tipus de sistemes de pantalla: 1) L'Oculus Rift; 2) Una gran pantalla estereoscòpica. Dos estudis van ser dissenyats. El primer estudi (N=89) va avaluar la memòria a curt termini i espacial utilitzant l'Oculus Rift i els dos tipus d'interacció. Els resultats indiquen que hi havia diferències significatives entre les dues condicions. Els participants que van utilitzar la condició2 van obtenir millor rendiment que els participants que van utilitzar la condició1. Tanmateix, no hi havia diferències significatives dins satisfacció i puntuacions d'interacció entre les dues condicions. El rendiment de la tasca va correlacionar amb el rendiment en les proves neuropsicològiques clàssiques, revelant versemblança entre elles. El segon estudi (N=59) va implicar participants que van tenir i que van haver-hi no estereopsis. Aquest estudi va avaluar la percepció de profunditat comparant els dos sistemes de pantalla. Els participants realitzen la tasca utilitzant la condició2. Els resultats van mostrar que les diferents característiques del sistema de pantalla no va influir en el rendiment en la tasca entre els participants qui tenien i els qui no tenien estereopsis. Diferències significatives van ser trobades a favor del HMD entre les dues condicions i entre els dos grups de participants. Els participants que no van tenir estereopsis i no podien percebre la profunditat quan van utilitzar altres sistemes de pantalla (per exemple, CAVE), van tenir la il.lusió de percepció de profunditat quan van utilitzar l'Oculus Rift. L'estudi suggereix que per les persones que no van tenir estereopsis, el seguiment del cap influeix en gran mesura en l'experiència 3D. Els resultats estadístics dels dos estudis han provat que el sistema de RV desenvolupat per aquesta recerca és una eina apropiada per avaluar la memòria espacial a curt termini i la percepció de profunditat. Per això, els sistemes de RV que combinen immersió plena, interacció i moviment poden ser una eina útil per la avaluació de processos cognitius humans com la memòria Les conclusions generals que s'han extret d'aquests estudis, són les següents: 1) La tecnologia de RV i la immersió proporcionada pels HMDs són eines apropiades per aplicacions psicològiques, en particular, la avaluació de memòria espacial a curt termini; 2) Un sistema de RV com el presentat podria ser utilitzat com a eina per avaluar o entrenar adults en habilitats relacionades amb la memòria espacial a curt termini; 3) Els dos tipus d'interacció utilitzats per navegació dins del laberint virtual podrien ser útils per al seu ús amb diferent col.lectius; 3) L'Oculus Rift permet que els usuaris que no tenen estereopsis puguen percebre la percepció de profunditat dels objectes 3D i tenirCárdenas Delgado, SE. (2017). VR systems for memory assessment and depth perception [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/94629TESI

Effects of diabetes and aging on posture and acceleration thresholds during lateral translations

Research objectives. One source of falls in the elderly may be an inability to sufficiently adjust to transient postural perturbations or slips. Identifying useful predictors of fall potential, as well as factors that affect the ability of an individual to detect a movement of the standing support surface may provide insight into postural stability and methods to increase stability in elders. To do this, acceleration thresholds to short, precise, lateral platform translations and the resultant psychophysical responses of adults with early Type 2 diabetes to age-matched controls and young adults were measured. Methods. Using an innovative SLIP-FALLS platform, short (1, 2, 4, 8,and 16mm) lateral perturbations were presented to 21 individuals—9 young adults, 6 neurologically intact elder adults, and 6 elders with diabetes using a two-alternative forced choice (2AFC) protocol. All subjects underwent lower-limb nerve conduction velocity determination, air conduction velocity testing, Semmes-Weinstein monofilament thresholds, the Mini Mental Status Exam, and reaction time tests to touch, tone and high acceleration, 4mm super-threshold perturbations. Results. All three groups had significantly different thresholds at all small (\u3c4mm) movement lengths, with the diabetic neuropathy group having a markedly higher acceleration threshold (P \u3c 0.001); the healthy elderly, which, in turn, had markedly higher thresholds than young adults. Patients with neuropathy had significantly higher reaction times to platform movements and touches to the plantar sole, but not for auditory tones. Both elderly groups had a significantly higher reaction time to superthreshold platform movement than did young adults. Sensory tests revealed slower nerve conduction velocities, higher air conduction velocities, and lower cognitive ability in the diabetic group. Conclusions. A marked decrease in perception of very small moves due to aging and diabetic neuropathy could well have a detrimental effect on postural control mechanisms. The higher prevalence of falls in the elderly and elderly diabetics may be due to decreased perceptual ability, slower nerve conduction velocities, and slowing reaction times compounded by larger amounts of imparted energy needed for detection of a slipping event

Human visual-vestibular interactions during postural responses to brief falls

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaves 263-276.by Roger William Wicke.Ph.D

Perturbation-evoked cortical responses are associated with balance ability in healthy young adults and in older adults with Parkinson's disease

Balance and cognitive impairments negatively impact quality of life in old age and in Parkinson's disease (PD) and are associated through unknown mechanisms. Measuring brain activity during reactive balance recovery may yield insight into the relationship between balance and cognitive function, facilitating the development of better treatment strategies. Electroencephalography (EEG) recordings show that sudden perturbations to standing balance reliably evoke a cortical N1 response localized to the supplementary motor area. The cortical N1 response is known to be influenced by cognitive processes because it is smaller when perturbations are predictable and enhanced when people are afraid or paying more attention to balance. Because the cortical N1 response is evoked by balance perturbations and influenced by cognition, it has the potential to reflect a site of interaction between balance and cognitive function. Despite knowledge of these cognitive influences on the cortical N1 response, there are no existing theories of how the cortical N1 response might influence subsequent balance recovery behavior. Through a series of studies, I present a novel hypothesis that perturbation-evoked cortical responses reflect cortical contributions to balance recovery, which are greater in people with lower balance ability. First, I show in healthy young adults (HYA) that a very small proportion of the cortical N1 response amplitude can be explained by the magnitude of sensory inputs, and that cortical N1 responses differ to a much larger extent between individuals. Then, I demonstrate that cortical N1 responses are larger for HYA who have lower balance ability, and that the cortical N1 response is larger when people take compensatory steps, suggesting that the cortical N1 response may reflect the need for cortically-mediated compensatory motor outputs. Then, I show that perturbation-evoked cortical responses in older adults with and without PD contain two component peaks, with smaller amplitudes of the second peak reflecting balance impairment in PD. Finally, I show that perturbation-evoked cortical responses are impacted by PD in a different manner than a related cortical response called the error-related negativity, which occurs when mistakes are made in computer-based cognitive tasks. The basic science work presented in this thesis may inform future studies into the relationship between balance and cognitive impairments, thereby facilitating the development of better rehabilitation strategies for balance impairments in Parkinson's disease.Ph.D

The role of short latency reflexes in the motor control of quadriceps in humans

A total of 34 volunteer subjects participated in a series of experiments. These experiments were designed to investigate the characteristics and functional role of an excitatory reflex pathway linking the pretibial muscles to quadriceps (CPQ reflex). The CPQ reflex was evoked by low intensity electrical stimulation of common peroneal nerve (CPN) at the level of caput fibulae. The reflex was observed in averaged EMG of rectus femoris (RF) and vastus medialis (VM). Voluntary contraction of Q was needed to reveal the reflex and no responses were detected in the recordings from relaxed muscle. The peak to peak amplitude and area of the responses were measured in non-rectified and rectified averaged EMG. The stability of the CPQ reflex was investigated in the first series of experiments. Nine trials were distributed across three sessions with the perceptive caution to keep the stimulating and recording conditions similar. A constant contraction (20% of maximum voluntary contraction) in quadriceps was maintained by the subjects during the tests. Constant stimulus intensity to evoke maximum reflex was applied in all trials. The result suggested that the peak- peak amplitude and the threshold of the CPQ reflex was extremely consistent with-in session and between sessions of the experiment. Graded stimulus intensities between 0.9 and 1.5xmotor threshold (MT) in tibialis anterior (TA) were applied to CPN in the second series of experiments while the quadriceps (Q) was contracted at a level of 20% of maximum voluntary contraction (MVC). The electrical stimulation of the CPN evoked excitatory responses in all the subjects with a latency of about 30+/-2.1ms (mean +/- ISD). The responses were regarded significant with amplitude beyond 2 standard deviation (SD) of the mean. The mean was calculated from 30ms pre-stimulus averaged EMG. In three subjects making contractions at 20% of MVC significant CPQ reflexes were recorded with stimulation at an intensity of 0.9xMT. The extrapolation of the pooled data also suggests an electrical threshold of around O.8xMT. This low threshold and the short latency strongly suggest the participation of group I afferent types in this reflex pathway. Maximum response was evoked by stimulus intensity of about 1.3XMT. The changes in the reflex magnitude in different knee and hip joint positions were also investigated in another series of experiments. The knee positioning was shown to affect the reflex amplitude in all subjects. The reflex became smaller towards more flexed position of the knee joint. Two patterns of reaction were recognised among the subjects. One group showed a very significant and abrupt reduction in the magnitude of the reflex after 1

Orbital research centrifuge. Experiment performance options and cost, volume 3. Space shuttle compatible Experiment Performance Options (EPOS)

Cost comparisons and experiment performance options for space shuttle orbital research centrifug

Neuroprosthetic system to restore locomotion after neuromotor disorder

Neuromodulation of spinal sensorimotor circuits improves motor control in animal models and humans with Spinal Cord Injury (SCI) and Parkinson disease. Stimulation parameters are tuned manually and remain constant during motor execution which is suboptimal to mediate maximum therapeutic effects. Here, I present a novel neuroprosthetic system that enabled adaptive changes of neuromodulation parameters during locomotion and allowed to restore high-fidelity control over leg movements in paralyzed rats. Beyond the therapeutic potential, these findings provide a conceptual and technical framework to personalize neuromodulation treatments for other neurological disorders. Several limitations have restricted the development of neuroprosthetic systems for closed loop neuromodulation. (1) First, it required a mechanistic understanding of the relationships between stimulation features and the recruitment of specific sensorimotor circuits. I found that electrical neuromodulation primarily recruits afferent reflex pathways that lead to coordinated activity of leg muscles during stepping. Moreover, the specific electrode location on the spinal cord could activate distinct reflex pathways and activate specific leg muscle groups of paralyzed rats. These results have been leveraged for the design of flexible and stretchable multi-electrode arrays for electrical and chemical spinal cord stimulation. (2) Second, it was necessary to perform comprehensive mapping experiments to characterize the effect of neuromodulation parameters on hind limb kinematics in order to establish stable and robust feedback signals for real time control. Step height and ground reaction forces emerged as the primary targets for the control of closed loop neuromodulation after spinal cord injury. (3) Third, implementation and optimization of closed-loop neuromodulation strategies necessitated the development of an advanced technological platform that combined feedback and feed-forward loops that match the natural flow of information in the modulated neural systems. These integrated developments allowed animals with complete spinal cord injury to perform over 1000 successive steps without failure, and to climb staircases of various heights and lengths with precision and fluidity. Moreover, the neuroprosthetic system was able to alleviate locomotor deficits in an alpha-synuclein rodent model of Parkinsonâs disease. Current knowledge of human spinal cord properties in response to electrical neuromodulation suggests that the developed control policies can translate into clinical applications to improve neurorehabilitation therapies. Moreover, the developed neuroprosthetic system can readily be interfaced with control signals from the brain to establish cortico-spinal neuroprostheses that are intended to promote activity-dependent plasticity during recovery from spinal cord injury