Browsing by Subject "neurological disorders"

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    Electrode - Fiber Distance and Active Unit Conduction Velocity Estimation
    (Office of the Vice Chancellor for Research, 2010-04-09) Qiao, Shaoyu; Yoshida, Ken
    Advanced neuroprosthetic electrodes are indwelling devices that are being developed to create a bidirectional interface to the nervous system. They are a key enabling technology under development to restore function to those suffering from neurological disorders or injury, and have the potential to restore function to paralyzed limbs, sight to the blind, or hearing to the deaf. Their ultimate performance is dictated by keeping the distance between the active sites on the implant structure and the target nerve cell minimized. Currently, there is no analytical way to evaluate the distance between the electrode and the active cell without histologically examining the implanted tissue post-mortem. We report here on the development of a method to estimate not only the distance, but also the conduction velocity of the action potential. A tissue filter relationship was derived through analysis of the reciprocity equations in the frequency domain and transformation of the spatial frequency to time frequency. The derived function relates how the SFAP is transformed as a function of distance and conduction velocity. A 3-D finite element (FE) volume conductor model of an electrode residing in a nerve fascicle was created to determine the potential distribution in the nerve fascicle, and derive the tissue filter function. Single fiber action currents were filtered using the tissue filter function to simulate the predicted action potential for different fiberelectrode distances and action potential conduction velocities. A power spectral density (PSD) analysis was then implemented for the simulated SFAPs, to quantify changes in the PSD of the recorded simulate SFAPs. The model shows that a smaller electrode-fiber distance results in the broader bandwidth signal. It further showed that the faster conducting fiber, the fewer weights the spatial filter function and the broader the bandwidth. These factors result in a quantitative change in the PSD of faster conducting fibers, resulting in a peak in modulation in the 2nd peak of the PSD (around 5-6 kHz) which is a function of velocity and distance. Through the use of multiple electrode sites, the conduction velocity can be predicted and differentiated from the effect of distance.
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    NEROPATHOLOGICAL APPROACH FOR BLAST-WAVE INDUCED MILD BRAIN INJURY
    (Office of the Vice Chancellor for Research, 2012-04-13) Meece, Callie; Chen, Jinhui; Gao, Xiang
    Veterans of Iraq and Afghanistan are extremely susceptible to complica-tions derived from blast-wave induced mild traumatic brain injury (mTBI) sustained from road-side bombs and IEDs. Furthermore, there are 1.5 mil-lion civilian incidences of TBIs annually in the United States, and as many as nearly 75% of them are mTBIs. An mTBI is an important medical concern because it can lead to long-term cognitive, emotional difficulties and behav-ioral disturbances. Neuroimaging with CT or MRI is usually negative. That is why mTBI has been called an “invisible wound.” There are no effective treatments for these disorders, partially due to the fact that the pathological basis leading to neurological disorders are poorly understood. Using a blast-wave injury model, several mice were given injuries similar to those from the front lines. The damaged brains were collected, mounted, stained, and imaged to track the dendrite and spine degeneration, both over all and by type of spine. After quantification, the results showed that the injured brain is intact without showing dramatic lesion or cell death, however, when we further assessed the morphologies of the spared neurons by using Golgi staining to visualize the individual neurons including their processes and spines in a very high resolution, we found that the dendrites of the spared neurons in the injured cortex demonstrated dramatic swelling with beading, a hallmark of dendritic injury, and there was a significant decrease in the number of mature (mushroom) spines, as well as a significant decrease in the overall number of spines. The function of the central nervous system critically relies on the synaptic connection from the different neurons be-tween the spines. The widespread synapse loss disrupts neural circuitry fol-lowing mTBI and will certainly contribute to neurological disorders. Our re-sults showed that mild blast-wave induced injury led to extensive dendrite degeneration and synapse reduction in the cortex in an animal model. This experimental study sheds light on the neuropathology of mild TBI in humans, and suggests that neurodegeneration may be a novel target for developing diagnostic methods and therapeutic approaches for mTBI in the future.