Circuits And Methods For Artifact Elimination

Disclosed are apparatus and methods that provide the ability to electrical stimulate a physical system, and actively eliminate interference with signal acquisition (artifacts) that arises from the stimulation. The technique implemented in the circuits and methods for eliminating interference connects a discharge path to a physical interface to the system to remove charge that is built-up during stimulation. By placing the discharge path in a feedback loop that includes a recording preamplifier and AC-coupling circuitry, the physical interface is brought back to its pre-stimulation offset voltage. The disclosed apparatus and methods may be used with piezoelectric transducers, ultrasound devices, optical diodes, and polarizable and non-polarizable electrodes. The disclosed apparatus can be employed in implantable devices, in vitro or in vivo setups with vertebrate and invertebrate neural tissue, muscle fibers, pancreatic islet cells, osteoblasts, osteoclasts, bacteria, algae, fungi, protists, and plants.Georgia Tech Research Corporatio

Bidirectional Neural Interface Circuits with On-Chip Stimulation Artifact Reduction Schemes

Bidirectional neural interfaces are tools designed to “communicate” with the brain via recording and modulation of neuronal activity. The bidirectional interface systems have been adopted for many applications. Neuroscientists employ them to map neuronal circuits through precise stimulation and recording. Medical doctors deploy them as adaptable medical devices which control therapeutic stimulation parameters based on monitoring real-time neural activity. Brain-machine-interface (BMI) researchers use neural interfaces to bypass the nervous system and directly control neuroprosthetics or brain-computer-interface (BCI) spellers. In bidirectional interfaces, the implantable transducers as well as the corresponding electronic circuits and systems face several challenges. A high channel count, low power consumption, and reduced system size are desirable for potential chronic deployment and wider applicability. Moreover, a neural interface designed for robust closed-loop operation requires the mitigation of stimulation artifacts which corrupt the recorded signals. This dissertation introduces several techniques targeting low power consumption, small size, and reduction of stimulation artifacts. These techniques are implemented for extracellular electrophysiological recording and two stimulation modalities: direct current stimulation for closed-loop control of seizure detection/quench and optical stimulation for optogenetic studies. While the two modalities differ in their mechanisms, hardware implementation, and applications, they share many crucial system-level challenges. The first method aims at solving the critical issue of stimulation artifacts saturating the preamplifier in the recording front-end. To prevent saturation, a novel mixed-signal stimulation artifact cancellation circuit is devised to subtract the artifact before amplification and maintain the standard input range of a power-hungry preamplifier. Additional novel techniques have been also implemented to lower the noise and power consumption. A common average referencing (CAR) front-end circuit eliminates the cross-channel common mode noise by averaging and subtracting it in analog domain. A range-adapting SAR ADC saves additional power by eliminating unnecessary conversion cycles when the input signal is small. Measurements of an integrated circuit (IC) prototype demonstrate the attenuation of stimulation artifacts by up to 42 dB and cross-channel noise suppression by up to 39.8 dB. The power consumption per channel is maintained at 330 nW, while the area per channel is only 0.17 mm2. The second system implements a compact headstage for closed-loop optogenetic stimulation and electrophysiological recording. This design targets a miniaturized form factor, high channel count, and high-precision stimulation control suitable for rodent in-vivo optogenetic studies. Monolithically integrated optoelectrodes (which include 12 µLEDs for optical stimulation and 12 electrical recording sites) are combined with an off-the-shelf recording IC and a custom-designed high-precision LED driver. 32 recording and 12 stimulation channels can be individually accessed and controlled on a small headstage with dimensions of 2.16 x 2.38 x 0.35 cm and mass of 1.9 g. A third system prototype improves the optogenetic headstage prototype by furthering system integration and improving power efficiency facilitating wireless operation. The custom application-specific integrated circuit (ASIC) combines recording and stimulation channels with a power management unit, allowing the system to be powered by an ultra-light Li-ion battery. Additionally, the µLED drivers include a high-resolution arbitrary waveform generation mode for shaping of µLED current pulses to preemptively reduce artifacts. A prototype IC occupies 7.66 mm2, consumes 3.04 mW under typical operating conditions, and the optical pulse shaping scheme can attenuate stimulation artifacts by up to 3x with a Gaussian-rise pulse rise time under 1 ms.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147674/1/mendrela_1.pd

Design of Integrated Neural/Modular Stimulators

Ph.DDOCTOR OF PHILOSOPH

Accessibility and Manipulation of Brain Signals for Neuroprosthetic Applications.

The field of Neural Engineering spawned in response to the perpetual problem of neurology: injured central nervous system neurons do not regenerate or repair, and stem cell/molecular genetic solutions, while the ideal intervention, are far away from clinical utilization. A current solution is to substitute computers and electrodes for neurons, as either transducers (cochlear implants, retinal implants, and visual cortex ECoG implants for sensory replacement), regulators (deep brain stimulations for Parkinson's disease), and output signal readers (motor cortex neuroprosthetics). I have focused on improving the technology of motor neuroprosthetics, and in this dissertation I investigated three sub-systems of this relatively new technology in a rat model. In my first experiment, I demonstrated that the cingulate cortex, part of the prefrontal cortex, can be used as an additional control signal for a motor neuroprosthetic device in the event that upper motor neurons of the motor cortex are degenerated by neurodegenerative diseases. In my second experiment, I examined whether electrocorticograms (ECoGs) and local field potentials (LFPs) are independent from the spiking activity of motor neurons and could be thus used as additional control channels. I showed these signals are not necessarily independent, specifically, the spikes phase-lock to the field potentials at defined frequencies, and careful algorithms will have to be developed to combine spikes, LFPs, and ECoGs as different control channels for a neuroprosthetic device. In my third experiment, I investigated the use of feedback in a neuroprosthetic model. I combined intracortical microstimulation (ICMS) of the visual cortex with simultaneous motor cortex ensemble recordings in real time to demonstrate the feasibility of a closed-loop neuroprosthesis. I showed that though sensory cortex ICMS can be combined with motor cortex recording in real-time in a viable preparation, increased technological development in simultaneous decoding with brain stimulation needs to occur before feasible clinical implementation can become a reality. By reading and manipulating brain signals via microelectrodes, a basic level of neural control and neural replacement can be achieved. Until the day that physicians have access to technology that allows spinal cords to regrow and limbs to regenerate, current technology allows us to achieve....Ph.D.NeuroscienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61629/4/tmarzull_2.pd

Microstimulation and multicellular analysis: A neural interfacing system for spatiotemporal stimulation

Willfully controlling the focus of an extracellular stimulus remains a significant challenge in the development of neural prosthetics and therapeutic devices. In part, this challenge is due to the vast set of complex interactions between the electric fields induced by the microelectrodes and the complex morphologies and dynamics of the neural tissue. Overcoming such issues to produce methodologies for targeted neural stimulation requires a system that is capable of (1) delivering precise, localized stimuli a function of the stimulating electrodes and (2) recording the locations and magnitudes of the resulting evoked responses a function of the cell geometry and membrane dynamics. In order to improve stimulus delivery, we developed microfabrication technologies that could specify the electrode geometry and electrical properties. Specifically, we developed a closed-loop electroplating strategy to monitor and control the morphology of surface coatings during deposition, and we implemented pulse-plating techniques as a means to produce robust, resilient microelectrodes that could withstand rigorous handling and harsh environments. In order to evaluate the responses evoked by these stimulating electrodes, we developed microscopy techniques and signal processing algorithms that could automatically identify and evaluate the electrical response of each individual neuron. Finally, by applying this simultaneous stimulation and optical recording system to the study of dissociated cortical cultures in multielectode arrays, we could evaluate the efficacy of excitatory and inhibitory waveforms. Although we found that the proximity of the electrode is a poor predictor of individual neural excitation thresholds, we have shown that it is possible to use inhibitory waveforms to globally reduce excitability in the vicinity of the electrode. Thus, the developed system was able to provide very high resolution insight into the complex set of interactions between the stimulating electrodes and populations of individual neurons.Ph.D.Committee Chair: Stephen P. DeWeerth; Committee Member: Bruce Wheeler; Committee Member: Michelle LaPlaca; Committee Member: Robert Lee; Committee Member: Steve Potte

The Representation of Multimodal Tactile Sensations in the Human Somatosensory System

The sense of touch is critical to executing basic motor tasks and generating a feeling of embodiment. To construct touch percepts, the brain integrates information from tactile mechanoreceptors with inputs from other senses and top-down variables such as attention and task context. In this thesis, we investigate how these factors influence neural activity within the somatosensory system at different stages of tactile processing, using electrophysiological and behavioral data from a human tetraplegic participant implanted with microelectrode arrays. First, we find that neural responses to imagined touches of different types are decodable in the primary somatosensory cortex, ventral premotor cortex, and the supra-marginal gyrus, and these responses remain stable over many months. Following this analysis, the primary somatosensory cortex is explored in greater depth to better characterize early-stage cortical tactile processing. Touches to the arm and finger are examined during a passive task, in a variety of conditions including visually observed physical touches, physical touches without vision, and visual touches without physical contact. Analysis of the two touch locations suggests that touch encoding in primary somatosensory cortex may be less rigid than in the classical topographic view. Additionally, this experiment uncovers a modulatory effect of vision in the primary somatosensory cortex when it is paired with a physical touch, but no effect of vision alone. Finally, we investigate how visual information impacts artificial tactile sensations, which can be elicited using intra-cortical microstimulation to the primary somatosensory cortex. The ability to elicit reliable, naturalistic artificial touch sensations is vital to the implementation of a tactile brain-machine interface, which would benefit patients with spinal cord injury and others with somatosensory impairments. We find that visual information biases the qualitative percept of artificial stimulation towards an interpretation that is visually plausible. The temporal binding window between vision and stimulation is found to be larger when visual information is biologically relevant, suggesting that the brain’s ability to causally relate artificial stimulation to visual cues depends on visual context. Additionally, recordings from the primary somatosensory cortex indicate that visual information relevant to artificial stimulation is represented across contexts, during an active task. The effect of task on the responsiveness of the primary somatosensory cortex to visual information points to a role of attention in mediating early cortical tactile processing. In combination, the findings presented in this thesis provide insight into the basic neuroscience of how tactile experiences are constructed by the brain, suggesting that early tactile processing is influenced by multisensory, contextual factors. These findings also have clinical applications to developing a brain-machine interface capable of providing naturalistic sensations within a complex real world environment

Intra-Cortical Microelectrode Arrays for Neuro-Interfacing

Neuro-engineering is an emerging multi-disciplinary domain which investigates the electrophysiological activities of the nervous system. It provides procedures and techniques to explore, analyze and characterize the functions of the different components comprising the nervous system. Neuro-engineering is not limited to research applications; it is employed in developing unconventional therapeutic techniques for treating different neurological disorders and restoring lost sensory or motor functions. Microelectrodes are principal elements in functional electric stimulation (FES) systems used in electrophysiological procedures. They are used in establishing an interface with the individual neurons or in clusters to record activities and communications, as well as modulate neuron behaviour through stimulation. Microelectrode technologies progressed through several modifications and innovations to improve their functionality and usability. However, conventional electrode technologies are open to further development, and advancement in microelectrodes technology will progressively meliorate the neuro-interfacing and electrotherapeutic techniques. This research introduced design methodology and fabrication processes for intra-cortical microelectrodes capable of befitting a wide range of design requirements and applications. The design process was employed in developing and implementing an ensemble of intra-cortical microelectrodes customized for different neuro-interfacing applications. The proposed designs presented several innovations and novelties. The research addressed practical considerations including assembly and interconnection to external circuitry. The research was concluded by exhibiting the Waterloo Array which is a high channel count flexible 3-D neuro-interfacing array. Finally, the dissertation was concluded by demonstrating the characterization, in vitro and acute in vivo testing results of the Waterloo Array. The implemented electrodes were tested and benchmarked against commercial equivalents and the results manifested improvement in the electrode performance compared to conventional electrodes. Electrode testing and evaluation were conducted in the Krembil Neuroscience Centre Research Lab (Toronto Western Hospital), and the Neurosciences & Mental Health Research Institute (the Sick Kids hospital). The research results and outcomes are currently being employed in developing chronic intra-cortical and electrocorticography (ECoG) electrode arrays for the epilepsy research and rodents nervous system investigations. The introduced electrode technologies will be used to develop customized designs for the clinical research labs collaborating with CIRFE Lab.1 yea