Neurostimulation | EPFL Graph Search

Neurostimulation is the purposeful modulation of the nervous system's activity using invasive (e.g. microelectrodes) or non-invasive means (e.g. transcranial magnetic stimulation or transcranial electric stimulation, tES, such as tDCS or transcranial alternating current stimulation, tACS). Neurostimulation usually refers to the electromagnetic approaches to neuromodulation. Neurostimulation technology can improve the life quality of those who are severely paralyzed or have profound losses to various sense organs, as well as for permanent reduction of severe, chronic pain which would otherwise require constant (around-the-clock), high-dose opioid therapy (such as neuropathic pain and spinal-cord injury). It serves as the key part of neural prosthetics for hearing aids, artificial vision, artificial limbs, and brain-machine interfaces. In the case of neural stimulation, mostly an electrical stimulation is utilized and charge-balanced biphasic constant current waveforms or capacitively c

Fabrication and validation of an intraneural interface tailored for optic nerve stimulation

Eleonora Borda

Technological progress in materials science and microengineering along with new discoveries in neuroscience have contributed to restore lost or impaired sensory functions by closely interfacing with the nervous system. Electronic devices have begun to be integrated within the body to artificially reproduce or record the electrical encoding of neural signals, the language of the nervous system. This has allowed us to restore the impaired communication between the missing or defective organ and the brain. As evidence of this, cochlear implants have returned hearing to millions of people world wide. On the other hand, there is no suitable solution yet for the 43 millions people who are currently blind. Nevertheless, several research groups and companies are trying to tackle this issue. So far, different devices have demonstrated the capability of restoring a certain degree of artificial vision, however, with limited success in delivering meaningful improvements in daily life activities. This is because, unlike hearing, vision is an extremely complex sense and requires higher stimulation resolution. Limitations of retinal prostheses have pushed further the investigation of other targets along the visual pathway, such as the optic nerve, the thalamus and the visual cortex. Among these, our group has started to explore the possibility of stimulating the optic nerve. The main advantages are the direct stimulation of the axon fibers and the access to the entire visual field with only one device. It is also interesting because it could work for those patients who are not eligible for retinal prostheses, due to severe eye trauma or retinal detachment, and it does not require optical transparency.In this thesis, we investigate stimulation strategies and materials to improve the outcome of optic nerve prostheses and make them one step closer to a viable option for blind patients. We first propose the use of machine learning algorithms to classify cortical activity upon electrical stimulation of the optic nerve. Secondly, we investigate a strategy to achieve higher spatial selectivity of the optic nerve stimulation. We design a three-dimensional (3D) multilayer concentric bipolar (CB) configuration and fabricate a modified version of the OpticSELINE. We validate the efficacy of the novel design during in-vivo experiments on rabbits and find that cortical activation is reduced when using the 3D multilayer CB electrodes compared to the classic monopolar configuration. In parallel, we explore the use of novel polymers, namely Off-Stoichiometry Thiol- Ene Epoxy (OSTE+), to design conformable neural interfaces. Their chemistry makes them a suitable candidate for easy integration in cleanroom processes and they show superior adhesion properties with respect to standard thin films currently in use. Hence, we characterise their usability as substrate and encapsulation for neural interfaces in-vitro and in-vivo. Lastly, we propose an alternative fabrication technique, ink-jet printing of platinum on flexible substrates, for neurophysiology applications. Altogether, the findings highlighted in this thesis will hopefully lead to a more in-depth investigation of the optic nerve prosthesis and can also be relevant for other applications in the field of neuroprosthetics.

EPFL2022

System Design and Advanced Circuit Techniques for Bi-Directional Brain-Machine Interfaces

Wen-Yang Hsu

Bi-directional brain-machine interfaces (BBMIs) that can capture electrophysiological signals and provide feedback through electrical stimulation are emerging tools with various applica-tions in fundamental neuroscience research as well as in clinical treatments of neurological dis-orders. The strict requirements originating from the specific and vast application range of these systems pose severe constraints to the development of portable or implantable microelectronic devices in terms of safety and reliability, autonomy, critical physical dimensions. The power consumption of BBMI systems should be minimized to comply with safety require-ments and enable long-term operations in an energy-constraint environment. In addition, specific physical dimensions and the interconnect reduction are crucial to fully exploit novel MEMS technologies to forge BBMIs aiming at different applications. Both bottom-up and top-down improvements are mandatory contributors of innovations on critical circuit blocks and system-level optimization, respectively. The first part of this thesis presents a BBMI targeting for a specific clinical application, namely, deep brain stimulation which has been proven to effectively alleviate neurological disorders such as essential tremor and Parkinsonâs disease. A novel MEMS technology which encom-passes a 3-dimensional brain region is employed to enhance the localization of the stimulation site. In order to fully exploit this technology, system requirements such as the strict device di-mension, highly-limited inter-connects and simultaneous recordings from 5 channels at low-power consumption pose several challenges on the custom electronics. Using a single supply voltage, an application-specific integrated circuit (ASIC) shaped into a specific aspect ratio is presented to tackle the aforementioned challenges. While the presented work is suitable for open-loop operations which demand frequent post-surgery programming for optimized therapeutic effects, closed-loop approaches directly re-sponding to the recorded signals offers better patient experience. Such autonomous BBMIs require long-term operation in an energy-constrained environment as well as intensive compu-tations on data processing. Innovations on critical blocks such as recording front-ends and stimulators are thus highly desirable to achieve an aggressive power reduction. A novel high-frequency, switched-capacitor (HFSC) stimulation and active charge balancing scheme is proposed. It achieves a high energy efficiency and well-controlled stimulation charge in the presence of large electrode impedance variations. Furthermore, the HFSC can be imple-mented in a compact size without any external component to simultaneously enable multi-channel stimulation by deploying multiple stimulators. The proposed design shows significant benefits over the constant-current and voltage-mode stimulation methods. Finally, a time-based and digitally-intensive recording front-end is presented, which employs the pulse-width modulation (PWM) to generate a timing-encoded binary output. The proposed design achieves low-power operation using a highly scaled technology with a sin-gle 0.5V supply voltage, favorable for system integration in energy-constraint BBMI applications.

EPFL2018

Investigation of electrical stimulation of the optic nerve for artificial vision

Vivien Gaillet

Thanks to recent technological advances in microelectronics and bioengineering, it is now possible to restore lost or impaired sensory modalities by interfering the nervous system with elec-tronic devices and artificially reproducing the electrical encoding of the neural signals of the missing or defective sensory organs or tissues, as evidenced by the successful development of cochlear im-plants allow the restoration of hearing in deaf patients. This makes the treatment of blindness, a very impairing condition that significantly decreases the quality of life of the person it affects, a plausible possibility today, and many groups are currently attempting to apply the same principle of cochlear implants to sight restoration. So far, the preferred approach has been retinal implants due to their proximity to the defective cells, the photoreceptors, which minimizes the amount of processing of the neural signal that needs to be reproduced, and due to the reasonable number of stimulating sites that the retina can accommodate. Several devices have already demonstrated the possibility of restor-ing some degree of functional vision, albeit still very rudimentary. However, unlike hearing, vision is an extremely complex sensory modality, involving several cell types forming elaborate circuitry, which makes the advantages of retinal implants less definitive, and other alternative approaches such as op-tic nerve of cortical prosthesis still worth exploring. We believe the optic nerve stimulation is an at-tractive approach for several reasons; firstly, it does not require optical transparency. Secondly, it can address specific conditions such as severe eye trauma or retinal detachment where retinal implants cannot be employed. Finally, thanks to the organization of the optic nerve axonal fibers, it may likely result in the activation of axons originating from the same region of the visual field. This is not the case with epiretinal implants, which have been reported to stimulate undesired axons of passage in addition to the somas of their cellular targets, resulting in curved and elongated phosphenes that lim-it the implant's achievable resolution. In this thesis, we introduce a novel intraneural electrode design, the OpticSELINE, which aims at im-proving the selectivity and stability of the extra-neural cuff-electrodes previously used in optic nerve stimulation. We first characterized the device's improved mechanical and electrical properties and then proceeded to evaluate its stimulation capacity in vivo in the rabbit. In parallel to demonstrating the ability to modulate the magnitude of the cortical activation through the increase or decrease of the stimulation current, we implemented a hybrid finite element computational model to estimate the dimensions of the nerve portions activated by our electrical stimulation protocols. Using inde-pendent component analysis (ICA), we also developed a workflow that allows isolating components of the signal selectively related to a single or a pair of stimulating electrodes. We then focused on the development of new and improved algorithms to analyze the cortical activation patterns. We first developed a support machine vector (SVM)-based classifier that allowed us to accurately identify both the visual stimulus or the stimulating electrode that elicited a given cortical activation pattern amongst ten and eight total potential stimuli. Finally, we developed a regression model that also al-lowed us to accurat

EPFL2021