Neural Interface With The Peripheral Nervous System PDF Download

The brain is a wondrous and complex organ, a biological machine forged by the evolutionary forces of nature. The human brain contains 100 billion neurons and each neuron is connected by synapses to several thousand other neurons. Connected neurons work together to produce perceptions and sensations, memories and emotions, physical movements and abstract constructs. The neurons communicate by means of electricity that passes along and across their cellular membrane. Much of what is known about brain physiology is through the measurement of this electrical activity, either with relatively large electrodes placed on the scalp or tiny microelectrodes inserted into the brain tissue itself. At the finer end of this scale, scientists have discovered much about the way individual neurons extract sensory information, adapt their behavior to form a memory, and convey signals to other regions of the brain. However, it has long been recognized that the brain operates on a global scale, through the collective behavior and interaction of its neural units1. Information is processed in several regions of the brain simultaneously, and the activity of neighboring neurons can be quite different from one another. By one analogy, the attempt to assess brain function by observing a single neuron is like looking at the output of one transistor to learn how a computer works. Thus, the recording of many neurons simultaneously is necessary to truly reveal the mechanisms of the brain2. In recent decades, a variety of recording techniques have been developed for a neural interface such as electroencephalography (EEG), magneto-encephalography (MEG), electrocorticography (ECOG), local field potential (LFP) recordings, micro-electrode array (MEA) and peripheral nerve interfaces (PNIs) to the micron-level precision required for multi-neuron recording. Their small size allows many recording channels to be placed onto one device. One of the goals of neural interface research is to create a seamless connection between the nervous system and the neuroprostheses either by stimulating or by recording from neural tissue to restore or substitute function for individuals with neurological deficits or disabilities. Hence, significant amount of scientific and technological efforts have been devoted to develop neural interfaces that link the nervous system with robotic prosthetic devices. The creation of a novel neural interface is essential for developing the full potential of advanced prosthesis technology required to replace lost limbs. Additionally, meticulous studies of a single neuron and between neurons utilizing the neural interface technology should be made to elucidate fundamental biological phenomena such as cellular processes and heterogeneities. Particularly, an electrophysiological study of neural networks can provide knowledge to unravel the functions of brain. When fundamental research about molecular and cellular mechanisms of a single neuron and electrophysiological studies using neural interfaces on both the central and peripheral nervous systems are done together, it has a synergistic effect on neural interface technology. The research and methodologies described in this dissertation stem from our research group's efforts to optimize the design and expand the applications of neural interfaces. The dissertation is organized into four chapters. Chapter 1 is a review of neural interface technology and study of neural signal detection. This chapter provides a foundation for Chapter 2 and 3. Chapter 2 is a study of a neural interface as cellular level research. We present an advanced single-neuronal cell culture and monitoring platform using a fully transparent microfluidic dielectrophoresis (DEP) device for unabated monitoring of neuronal cell development and function. The device is mounted inside a sealed incubation chamber to ensure improved homeostatic conditions and reduced contamination risk. Consequently, we successfully trap and culture single neurons on a desired location and monitor their growth process over a week. Chapter 3 deals with the specific application of PNIs to the sciatic nerve of a rat as a nervous system-level research. We developed novel devices, "cuff and sieve electrodes" (CASE), that integrate microfabricated cuff and sieve electrodes capable of broad (via cuff) and precise (via sieve) selectivity to increase the strengths and simultaneously decrease the weaknesses of traditional electrode designs. We performed terminal device implantations in a rat sciatic transection and repair model to test the capacity of the CASE interface. The sciatic nerve was stimulated by the sieve portion of the CASE electrode and somatosensory evoked potentials were recorded from the somatosensory cortex via micro-eletrocorticography. The ability to elicit cortical responses from sciatic nerve stimulation demonstrates the proof of concept for both the implantation and chronic monitoring of CASE interfaces for innovative prosthetic control. Lastly, in Chapter 4, I will identify areas in which further investigation is needed and propose future directions of both cellular and system-level neural interface.