Microelectronic vision prostheses aim to restore visual percepts through electrical stimulation of the surviving visual pathways in the blind. Electrical stimulation has been shown to produce spots of light in the visual field. A neurostimulator that forms the basis of a vision prosthesis was designed using a high voltage CMOS process to allow it to be able to stimulate when faced with high electrode-tissue impedances. It was implemented with novel features that allow it to be scalable, and to focus charge injection, and can stimulate multiple sites simultaneously using a current source and sink at each site. To reduce electrical cross-talk between multiple stimulation sites, six-return electrodes surround each stimulating electrode, electrically guarding them from each other. The six-return electrode configuration was shown to reduce electrical cross-talk in saline bath tests compared to single-return electrode configurations. The neurostimulator was used to evoke responses from cats through electrical stimulation via intravitreal ball electrodes, corneal electrodes, and planar electrode arrays in the suprachoroidal space. Responses were measured on the visual cortex through optical imaging of intrinsic signals, and through surface electrodes. Using the planar electrode array in the suprachoroidal space, responses were elicited to biphasic, bipolar and monopolar stimuli, with each stimulating electrode coupled with either six-return electrodes, two-return electrodes, or a single-return electrode. The average charge threshold to elicit a response for biphasic, bipolar stimulation with six-return electrodes was 76.47 ?? 8.76 nC (standard error of the mean). For biphasic, bipolar stimulation, the magnitude and area of cortical response with the six-return electrode configurations was on average 2.18 ?? 0.19 times smaller than single-return electrode configurations, and 1.89 ?? 0.19 times smaller than two-return electrode configurations (P < 0.0001). It was also found that for biphasic stimulation, a greater magnitude and area of response was elicited for monopolar stimulation compared to bipolar stimulation. This dissertation details the design and testing of a novel, scalable neurostimulator to focus charge injection. It also shows that suprachoroidal, bipolar stimulation can elicit visual responses, and that the area of cortical activation was more focused when using bipolar, biphasic stimulation, and six-return electrodes.

Use of electrically stimulated exercise following spinal cord injury is recommended for improving fitness, and can be enhanced by the addition of upper limb exercise. Laboratory trials of electrically stimulated leg cycling (ESLC) have led to increased oxygen uptake and carbon dioxide production, and reactivation of the venous muscle pump, increasing stroke volume and cardiac output during exercise. However transfer of these eftects into home and community settings has been poor. The Power Trainer, a commercially available device, combines active arm crank exercise (ACE) with ESLC, achieving hybrid exercise (HE). Despite its relative simplicity compared with legs only electrical stimulation cycles, exercise responses associated with its use have not been researched. The exercising muscle mass during HE with the Power Trainer is increased compared with either arms only or legs only exercise, increasing respiratory demands. If venous return is also increased, such exercise will fulfil the requirements for regaining fitness following a spinal cord injury. Differences were investigated between the cardiorespiratory responses to ACE and HE on the Power Trainer. Responses were measured during 30 minutes of steady state exercise with each exercise modality.

Electrical stimulation of retinal neurons is known to elicit visual sensations. When applied to the retina in a spatial pattern, electrical stimulation may be capable of providing rudimentary patterned vision that may be of benefit to sufferers of degenerative retinal disorders. No such device has yet been devised to provide for chronic study of the psychophysical perceptions elicited from a prosthesis for retinal stimulation. In this study, steps towards achieving this goal have been successfully carried out. Foregoing research was reviewed such that appropriate stimulation parameters were incorporated in the design of a 100 stimulation channel, complimentary metal oxide semiconductor (CMOS) integrated circuit, small enough in size so as to be capable of being implanted within the ocular anatomy or surrounding orbit. The device, and its associated external hardware and software were designed, modeled, fabricated, and interfaced with stimulating electrodes in acute testing in a highorder mammal (Ovis aries) so as to assess the capabilities of the device to elicit cortical potentials as a direct result of stimulation of the neural retina. Testing was performed under conditions similar to those anticipated in chronic in-situ configurations wherein radio-frequency telemetry was used to deliver power and configuration parameters to the device thus avoiding the passage of wires through tissue in order to communicate to the implant circuit. The results of the testing indicate that the circuit is indeed capable of eliciting physiological responses in the animal and evidence is present that these responses could be elicited in patterned form. Further work undertaken includes the development of surgical methods for implantation, and application of the prosthesis circuit in functional electronic stimulation.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Stuart A. Binder-Macleod, Dept. of Physical Therapy. Includes bibliographical references.

The current study examined cognitive effects of unilateral subthalamic nucleus (STN) deep brain stimulation (DBS) in Parkinson's disease (PD) patients. Neuropsychological evaluations were conducted at baseline and follow-up. Data was collected from 28 unilateral STN DBS patients (15 English- and 13 Spanish-speaking), and 15 English-speaking matched PD control patients. English-speaking DBS patients demonstrated significant declines in verbal fluency and attention/executive function, whereas PD control patients did not experience significant cognitive decline. Cognitive performance did not differ based on side of DBS. Spanish-speaking DBS patients experienced significant declines in verbal fluency, confrontational naming and visuospatial abilities. Among Spanish-speaking DBS patients, older age and later age of disease onset predicted verbal fluency decline, even after controlling for education.

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Stuart A. Binder-Macleod, Dept. of Physical Therapy. Includes bibliographical references.

Epilepsy, which manifests itself as spontaneous bouts of abnormal low complexity brain activity, is the second most common neurological disorder after stroke. This thesis explores the effect of variable frequency stimulation on seizure control. A responsive variable frequency electrical stimulation system is proposed and validated using a computational model capable of generating spontaneous seizure like events. The proposed stimulation system is demonstrated to outperform open-loop fixed frequency stimulation and responsive fixed frequency stimulation using seizure time based measures and a control energy measure.

Epilepsy, which manifests itself as spontaneous bouts of abnormal low complexity brain activity, is the second most common neurological disorder after stroke. This thesis explores the effect of variable frequency stimulation on seizure control. A responsive variable frequency electrical stimulation system is proposed and validated using a computational model capable of generating spontaneous seizure like events. The proposed stimulation system is demonstrated to outperform open-loop fixed frequency stimulation and responsive fixed frequency stimulation using seizure time based measures and a control energy measure.

A system for extracellular neural interfacing that had the capability for stimulation and recording at multiple electrodes was presented. As the core of this system was a custom integrated circuit (IC) that contained low-noise amplifiers, stimulation buffers, and artifact-elimination circuitry. The artifact-elimination circuitry was necessary to prevent the activity of the stimulation buffers from interfering with the normal functioning of the low-noise amplifiers. The integrated circuits were fabricated in in a 0.35 micron CMOS process. We measured input-referred noise levels for the amplifiers as low as 3.50 microvolts (rms) in the in the bandwidth 30 Hz-3 kHz, corresponding to the frequency range of neural action potentials. The power consumption was 120 microwatts, corresponding to a noise-efficiency factor of 14.5. It was possible to resume recording signals within 2 ms of a stimulation, using the same electrode for both stimulation and recording. A filtering algorithm to remove the post-discharge artifact was also presented. The filtering was implemented using a field-programmable gate array (FPGA). The filtering algorithm itself consisted of blanking for the duration of the stimulation and artifact-elimination, followed by a wavelet de-noising. The wavelet de-noising split the signal into frequency ranges, discarded those ranges that did not correspond to neural signals, applied a threshold to the retained signals, and recombined the different frequency ranges into a single signal. The combination of the filtering with the artifact-elimination IC resulted in the capability for artifact-free recordings.

As the demand for energy worldwide increases, the oil and gas industry will need to increase recovery from unconventional gas reservoirs (UGR). UGRs include Tight Gas Sand (TGS), coalbed methane and gas shales. To economically produce UGRs, one must have adequate product price and one must use the most current technology. TGS reservoirs require stimulation as a part of the completion, so improvement of completion practices is very important. We did a thorough literature review to extract knowledge and experience about completion and stimulation technologies used in TGS reservoirs. We developed the principal design and two modules of a computer program called Tight Gas Sand Advisor (TGS Advisor), which can be used to assist engineers in making decisions while completing and stimulating TGS reservoirs. The modules include Perforation Selection and Proppant Selection. Based on input well/reservoir parameters these subroutines provide unambiguous recommendations concerning which perforation strategy(s) and what proppant(s) are applicable for a given well. The most crucial parameters from completion best-practices analyses and consultations with experts are built into TGS Advisor’s logic, which mimics human expert’s decision-making process. TGS Advisor’s recommended procedures for successful completions will facilitate TGS development and improve economical performance of TGS reservoirs.