Thesis (Ph. D.)--Oregon State University, 2006. / Blank pages 143 and 159 not microfilmed. Includes bibliographical references. Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (Ph. D.)--Oregon State University, 2006. / Blank pages 143 and 159 not microfilmed. Includes bibliographical references.

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In order for stroke subjects to gain functional recovery of their hemiparetic limbs, facilitation techniques such as the repetitive facilitation exercise, or RFE, have been developed. Currently, there is a lack of understanding of the neural mechanisms associated with these types of facilitation techniques. To better understand the neural mechanisms associated with the RFE a functional magnetic resonance imaging (fMRI) study should be conducted. This thesis presents experimental results testing the feasibility of implementing an fMRI-compatible actuator to facilitate a myotatic reflex in synchronization with the subject’s intention to move their hemiparetic limb. Preliminary data from a healthy individual demonstrated the feasibility of overlapping the long latency component of the afferent myotatic reflex, created by electrical stimulation, with descending nerve impulses, created using transcranial magnetic stimulation, in a time window of 15ms. In addition, a pneumatic actuation time delay due to long transmission line was evaluated. The pneumatic actuator met the timing precision requirement for the rehabilitation device for varying transmission line lengths. Therefore a pneumatic actuation system was chosen for the rehabilitation device. This thesis will also presents on the design of an fMRI-compatible pneumatic actuator device to excite a stretch reflex response. Initial, experimental results with the device demonstrated that the designed pneumatic device can control the timing of the muscle response with a fixed signal within the required 15ms window required for cortical facilitation, which was found in the previous feasibility study. However, the device was unable to create a long latency reflex observable at the muscle. Finally, this thesis presents on the capability of the device in creating subthreshold long latency response with precision to overlap with a subthreshold descending nerve impulse, created using transcranial magnetic stimulation. The overlap of the two responses was evaluated by comparing the amplitude of the muscle response with and without the stretch reflex, created by the fMRI-compatible pneumatic actuator device. Varying time delays were analyzed.

It is known that muscles possess both intrinsic and reflexive responses to stretch, both of which have been studied extensively. While much is known about heterogenic and autogenic reflexes during XER, these have not been well characterized during locomotion. In this study, we mapped the distribution of autogenic and heterogenic feedback in hindlimb extensor muscles using muscle stretch in the spontaneously locomoting premammillary decerebrate cat. We used natural stimulation and compared stretch-evoked force responses obtained during locomotion with those obtained during XER. The goal was to ascertain whether feedback was modulated between the two states. We found that heterogenic feedback pathways, particularly those emanating from MG, remained inhibitory during locomotion while autogenic feedback specifically in MG increases in gain. Furthermore, increases in MG gain were due to force-dependent mechanisms. This suggests that rather than an abrupt transition from inhibition to excitation with changes in motor tasks, these pathways coexist and contribute to maintaining interjoint coordination. Increases in autogenic gain provide a localized loading reflex to contribute to the completion of the movement. The results of these experiments are clinically significant, particularly for the rehabilitation of spinal cord injured patients. To effectively administer treatment and therapy for patients with compromised spinal reflexes, a complete understanding of the circuitry is required.

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