Browsing by Author "Sivasankar, Manju"
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Item DESIGN OF THE MR-STRETCHFINGERS DEVICE FOR THE STUDY OF NEUROMECHANICS OF STRETCH REFLEXES IN THE FINGER MUSCLES(University of Delaware, 2023-05) Sivasankar, ManjuHuman motor control consists of feedforward and feedback mechanisms, both aiming to reach a desired muscle state. Feedforward control does not involve sensory feedback and instead generates a movement based on the desired state. In humans, feedforward control is involved in voluntary reactions to a stimulus [1]. By contrast, feedback control considers movement errors and sensory feedback, with the aim of correcting movements. However, feedback control occurs on several timescales, and the speed of these responses is constrained by the neuromuscular pathways required for producing them. One method of feedback control in humans is stretch reflexes. Long latency responses (LLRs) specifically are believed to occur due to a combination of inputs from the corticospinal tract (CST) and reticulospinal tract (RST). LLRs are important to study biomedically, as they are involved in many neurological diseases that affect voluntary motor control. The CST can be damaged due to stroke [3]. For instance, 50% of people who experienced a stroke have a residual motor disability which can be due to reduced corticospinal drive resulting in a loss of movement accuracy and muscle flaccidity [4]. The RST can assume some of the lost CST function; however, the RST’s role in regaining motor function is not well understood. Understanding the role these pathways play in finger control at the metacarpophalangeal (MCP) joint has not been extensively studied in the past. The goal of this project was to develop a device which would elicit long latency responses in participants, validate that these responses are elicited, and utilize fMRI imaging to map the neural pathways activated during perturbations. In Aim 1 we present the development of the MR-StretchFingers device, which aims to apply perturbations at the MCP joint. We then present results which show that the device specificationsare met and it is capable of applying perturbations at the MCP joint and limiting other movement within those specifications. In Aim 2, we examine the signal-to-noise ratio (SNR) measured using surface electromyography (sEMG) in two muscles: first dorsal interosseus muscle which aids with flexion of the index finger, and the flexor digitorum superficialis muscle, which aids with middle/ring/pinky finger flexion. Results show that SNR was maximal during flexion movements corresponding to either index or middle/ring/pinky flexion, matching the physiological understanding of the muscles. Further, the results were of similar magnitude to SNR values for other muscles in literature. We then present an LLR study, which aimed to determine if LLRs are being elicited. We found that LLRs were being elicited in all cases at the group level, in both FDI and FDS with background torque applied by either the index finger only or middle/ring/pinky fingers only. Finally, we present an MRI conditions pilot which aims to find a control and experimental condition suitable for fMRI imaging. The results indicate two conditions which were suitable. In Aim 3, we present an MRI pilot study, which involved simultaneous mechanical perturbations by the MR SF with fMRI. The results indicate that there is some activation in the motor cortex and brainstem due to LLR modulation. Overall, this study provides preliminary evidence that there is subcortical and cortical activity that modulates the LLRs elicited by finger muscles. Future studies can expand on these results by including more participants and fine tuning the pro tocol to provide a clearer understanding of the neural correlates of LLRs and how the LLR in finger muscles are modulated by factors such as the perturbation veloc ity. Further, other factors affecting LLRs, such as task instruction or varying levels of background torque can be examined both outside and inside the MRI to understand LLR modulation. These findings can increase our understanding of human secondary motor pathways and lead to new rehabilitation strategies and therapies that can aid individuals with various motor impairments.