The rat whisker system has been a longstanding and fruitful model system for sensory neuroscience, because of its status as an œexpert active sensing system, and many open avenues of research still remain. One large-scale goal of the field is to œclose the loop from sensation to movement, modeling how...
Each movement we make represents the final output of complex processes in the nervous system. Studies of motor control often attempt to minimize further complication by using controlled environments to generate repeated movements. However, in natural situations, the motor system faces the much more complicated task of interacting with an...
Diabetes mellitus is a metabolic disease characterized by the abnormal high blood glucose of patients. The defects in the hormonal regulation, including impaired insulin secretion, insulin action, or the combination of the two are usually the causes of such a disease. The elevated blood glucose also leads to a wide...
Currently, the only treatment for end stage liver disease is transplantation, of which there is a critical shortage of available donor tissue. Recent developments in 3D printing have greatly accelerated progress in the field of liver tissue engineering. A variety of 3D printing and additive manufacturing techniques show great promise...
Up to two thirds of individuals with chronic hemiparetic stroke suffer life-long residual impairments to their paretic hands, affecting their independence and quality of life. These impairments stem initially from losses of direct corticospinal projections that result in an increased reliance on indirect bulbospinal pathways. This reliance on the indirect...
The rodent whisker system is a widely used model to study the sense of touch. Its neuroanatomy parallels that of the human, but its mechanics are vastly simplified compared to that of the human tactile system. Just like other modalities with complex sensor accessory structures, the geometry, mechanics, and material...
Many stroke survivors are left with residual movement impairments. Treating these impairments has proven difficult, because it is often unclear which mechanisms drive movement impairment. While the exact mechanisms are still uncertain, at present, evidence suggests that neuromuscular function is disrupted in two key domains following stroke: muscle biomechanics, and...
Humans have a remarkable ability to walk on a variety of surfaces. Compliant, uneven, or even slippery surfaces present little challenge to most people, yet are hazardous to individuals with locomotor impairments and even to bipedal robotic systems designed to mimic what we understand about human locomotion. Our ability to...
Space, time and energy are the three most fundamental elements in our intellectual understanding of the physical world. Here, I found how these same elements also contribute to a stable and coherent representation that the motor system forms by combining information from different sensory sources, such as vision, touch and...
Paralysis resulting from spinal cord injury (SCI) is devastating, dramatically reducing the independence of affected individuals. Currently, functional electrical stimulation (FES), controlled by a patient’s residual movements, is used clinically to restore a limited range of voluntary movement. However, if FES could be controlled using signals recorded from the brain,...
The brain has a remarkable ability to rapidly adapt behavior. On the scale of development, the brain learns to control the complex dynamics of our limbs by forming and pruning synaptic connections. However, the motor system also learns on much shorter timescales, such as when learning to hit the bullseye...
Step length is a common measurement taken during gait analyses. It allows one to determine asymmetries between the two legs, compare differences between subjects, and even compare intra-subject differences for changing parameters. Yet there has been little investigation of step length specifically and how it is modulated during walking. This...
The objective of this study was to investigate how brain plasticity can be expressed following injury to the nervous system. This plasticity can occur after either direct injury to the brain, such as in hemiparetic stroke, or injury to the peripheral nerves, such as in upper-limb amputation. In order to...
Hepatocellular carcinoma (HCC) is the most common primary malignant liver tumor, with the highest incidence in Asia. Developed countries, including the United States, have had an 80% increase in HCC incidence over the last 15-20 years.
Magnetic Resonance Imaging (MRI) is a promising imaging modality with superior soft tissue...
All forces applied to the human hand are transmitted through the arm to the trunk. Hence, the arm represents an important mechanical interface between the trunk and the environment. By regulating this interface in a task-appropriate manner, humans are able to interact with a wide range of tools and objects,...
Coronary magnetic resonance angiography (MRA) is emerging as a promising method for noninvasive diagnosis of coronary artery diseases. Nonetheless, acquisition of large-coverage high-resolution coronary artery images requires free-breathing acquisition. Accurately measuring and correcting respiratory motion has been one of the major challenges to coronary MRA. Diaphragmatic navigator (NAV), the current...
A critical challenge in improving the quality of life for spinal cord injury survivors is to restore the capacity to grasp and manipulate objects. While progress has been made to restore hand function by using functional electrical stimulation (FES) to activate muscles, providing the means to control the multiple degrees...
Articular cartilage is a type of connective tissue that protects the underlying bone from the compressive forces of daily activities. When cartilage is damaged via a traumatic event, chondral defects are formed and require medical intervention. However, current treatments are of inconsistent efficacy and only benefit a subset of patients....
Caffeine is the most widely consumed methylxanthine, primarily found in beverages. As a nonspecific antagonist to adenosine, caffeine binds to both A1 and A2A adenosine receptors to increase neural activity and decrease cerebral blood flow, which allows it to alter neurovascular coupling. However, there has been much debate about the...
The adhesive strategies of living creatures are diverse, ranging from temporary to permanent adhesions with various functions such as locomotion, self-defense, communication, colony formation, and so on. The classic example of temporary adhesion is the gecko, which is known for its ability to walk along vertical and even inverted surfaces;...
Classical conditioning has been well studied over the last century as a method for investigating learning and memory. The rabbit eyeblink response is commonly used as a basis for such studies, and combined with lesions or electrophysiological recordings has provided a well-controlled paradigm for investigating the neurobiological mechanisms underlying learning...
Biological fouling of surfaces is problematic for many medical applications because proteins, cells and bacteria can impair the function of devices and lead to catastrophic complications. Numerous strategies exist for reducing fouling in physiological environments; the strategy described in this thesis focuses on the modification of substrates with poly-N-substituted glycine...
Despite three decades of intense research into small diameter blood vessel tissue engineering, constructs developed to date lack the elastin necessary for long term patency and the prevention of aneurysms. The suboptimal biochemical composition suggests that new biochemical and mechanical culture methods must be developed. In addition, current biomaterials for...
Short-range stiffness (SRS) of a skeletal muscle describes the muscle's capability to resist external perturbations before the nervous system can intervene. Knowledge of the SRS of individual muscles is critical in understanding their contributions to single joint stiffness and whole limb stability. While the dependence of SRS on muscle force...
During interactions with our environment we must incorporate information about the mechanical properties of obstacles into our motor actions. Fundamental to these behaviors is the ability to simultaneously control movements of the hand while regulating the interaction forces that arise from contact with the environment. Although the neural control of...
A need exists to increase the functionality of myoelectric prostheses without increasing the mental requirement of operation. Implantable myoelectric sensors have made it possible to record multiple muscle activities with high fidelity. Given this high dimensionality of inputs, what is the best way of implementing control? Muscle synergies have been...
Conventional perfusion magnetic resonance imaging with dynamic susceptibility using a contrast agents has been playing a dominant role on diagnosing a variety of cerebral nervous system disease due to lack of radiation and widespread availability. However, reliable quantification of cerebral perfusion has been elusive and challenging.
The bookend method is...
Age-related maculopathy (ARM) is a leading cause of legal blindness in the elderly in the world. Currently, the physiological and ultrastructural bases for the development of ARM remain unclear. Many studies have proposed that the morphological changes, particularly the accumulations of lipids with aging, in Bruch's membrane - an extracellular...
Intramuscular electromyograms (EMG) are believed to provide several potential advantages over surface EMG for multifunctional myoelectric prosthesis control. One example is the ability to focally record from deep muscles of the forearm. However, intramuscular EMG has rarely been investigated due to the inability to obtain chronic recordings. New technology is...
In indoor environments, bacteria face selective pressure to carry antibiotic resistant genes (ARGs) from antimicrobial substances used in furniture, building materials, and personal care products. Humans rely on antibiotics to clear bacterial infections, so understanding the way in which these genes are transferred, i.e., on mobile genetic elements, is critical....
Magnetic resonance imaging (MRI) allows for the selective visualization of blood vessels via the intravascular injection of a paramagnetic contrast agent and the suppression of background signal. Called magnetic resonance angiography (MRA), this technique can produce three-dimensional images and is useful clinically for the noninvasive diagnosis of vascular disorders. In...
Commercially available electrically powered prosthetic elbows are stiff and unyielding. Making these artificial limb replacements more closely mimic human elbows by increasing their compliance may be beneficial. In addition to having increased compliance compared with current electrically powered prosthetic elbows, humans modulate the overall impedance of their joints. The author...
The role that spinal motion plays during ambulation is not clearly understood. Little in vivo regional spinal motion data exists in the literature with regard to walking and most gait models disregard the upper body altogether, or regard it as a single rigid structure. This study aims to increase understanding...
Individuals with severe motor impairments often have a difficult time performing daily activities, and thus rely heavily on assistive devices to restore some functional independence. The two main limitations of the current controllers for assistive devices are: 1) controllers that do not require coordinated hand movement provide a limited vocabulary...
Regardless of how it may seem at times, the President of the United States is not in charge of all the major decisions made by the government. The laws that we must adhere to are made, formed, and passed by Congress which is composed of the House of Representatives and...
Over the past two decades, optical coherence tomography (OCT) has been successfully applied to various fields of biomedical researching and clinical studies, including cardiology, urology, dermatology, dentistry, oncology, and most successfully, ophthalmology. This dissertation seeks to extend the current OCT practice, which is still largely morphology-based, into a new dimension,...
Patients born with severe heart defects need regular monitoring of the complex hemodynamics in their heart and vasculature. 4D flow MRI has emerged as the state-of-the-art technique for comprehensively evaluating cardiovascular hemodynamics. This imaging technique allows for the dynamic visualization of 3D blood through the cardiac cycle and the quantification...
A stroke can occur at any point throughout the lifespan, including in utero. The timing of the injury relative to neural development can have implications on the type of lesion, plasticity, and motor deficits. However, associated reactions, which refer to involuntary movement in one limb in response to voluntary activity...
Spherical Nucleic Acids (SNAs) are nanoparticle bioconjugates that have found use in a wide-range of diagnostic and therapeutic applications. These nanomaterials are composed from inorganic or organic core nanoparticle scaffolds that are functionalized with a dense surface layer of nucleic acids (typically DNA or RNA) that are oriented in a...
Glaucoma is a neurodegenerative blinding disease associated with increased intraocular pressure, which is caused by an increased resistance to the outflow of aqueous humor. Although the cause for increased resistance remains unknown, it has been associated with a decreased density of pores in the cells of the inner wall endothelium...
Even though renal blood flow accounts for nearly a quarter of cardiac output, the renal medulla operates in an environment with a scant supply of oxygen. The reason for this apparent discrepancy is thought to be threefold. Blood flow to the outer medulla is less than 50% of that received...
Stroke is the leading cause of death and long term disability in the industrialized world. With the current population aging, the number of individuals at risk of stroke along with the associated health care costs are anticipated to rise considerably in the coming years. Consequently, there is an unmet need...
Pattern recognition algorithms have been proposed as a way to control powered lower limb prostheses, specifically for transitioning between the different pre-programmed locomotion modes of the prosthesis (e.g., level ground walking, stair ascent, etc.). However, these algorithms cannot track changes in the statistical characteristics of input signals, and do not...
Myocardial perfusion is an important marker of cardiovascular health that is routinely evaluated clinically. Perfusion is measured most often using single photon emission computed tomography (SPECT) imaging, but magnetic resonance imaging (MRI) has many advantages over SPECT. Measuring perfusion quantitatively in ml/min/g would theoretically allow for improved characterization of cardiac...
Pattern recognition-based myoelectric control of upper limb prostheses has been made clinically available to individuals with more proximal upper limb amputations and can restore intuitive control of a prosthetic hand. This control method has yet to be implemented for individuals with amputations distal to the wrist (i.e. partial-hand amputations) and...
It is becoming increasingly evident that the nanoscale organization and structure of macromolecules play a significant role in determining the function and properties of biological systems. To understand the relationships between biological structure and function at nanometer length scales, there is a need for methods which enable imaging of intact...