Electrical vestibular stimulation in humans. A narrative review

Background: In patients with bilateral vestibulopathy, the regular treatment options, such as medication, surgery, and/ or vestibular rehabilitation, do not always suffice. Therefore, the focus in this field of vestibular research shifted to electri- cal vestibular stimulation (EVS) and the development of a system capable of artificially restoring the vestibular func- tion. Key Message: Currently, three approaches are being investigated: vestibular co-stimulation with a cochlear im- plant (CI), EVS with a vestibular implant (VI), and galvanic vestibular stimulation (GVS). All three applications show promising results but due to conceptual differences and the experimental state, a consensus on which application is the most ideal for which type of patient is still missing. Summa- ry: Vestibular co-stimulation with a CI is based on “spread of excitation,” which is a phenomenon that occurs when the currents from the CI spread to the surrounding structures and stimulate them. It has been shown that CI activation can indeed result in stimulation of the vestibular structures. Therefore, the question was raised whether vestibular co- stimulation can be functionally used in patients with bilat- eral vestibulopathy. A more direct vestibular stimulation method can be accomplished by implantation and activa- tion of a VI. The concept of the VI is based on the technology and principles of the CI. Different VI prototypes are currently being evaluated regarding feasibility and functionality. So far, all of them were capable of activating different types of vestibular reflexes. A third stimulation method is GVS, which requires the use of surface electrodes instead of an implant- ed electrode array. However, as the currents are sent through the skull from one mastoid to the other, GVS is rather unspe- cific. It should be mentioned though, that the reported spread of excitation in both CI and VI use also seems to in- duce a more unspecific stimulation. Although all three ap- plications of EVS were shown to be effective, it has yet to be defined which option is more desirable based on applicabil- ity and efficiency. It is possible and even likely that there is a place for all three approaches, given the diversity of the pa- tient population who serves to gain from such technologies

Interactions of prosthetic and natural vision in animals with local retinal degeneration

Prosthetic restoration of partial sensory loss leads to interactions between artificial and natural inputs. Ideally, the rehabilitation should allow perceptual fusion of the two modalities. Here we studied the interactions between normal and prosthetic vision in a rodent model of local retinal degeneration.  Implantation of a photovoltaic array in the subretinal space of normally sighted rats induced local degeneration of the photoreceptors above the chip, and the inner retinal neurons in this area were electrically stimulated by the photovoltaic implant powered by near-infrared (NIR) light. We studied prosthetic and natural visually evoked potentials (VEP) in response to simultaneous stimulation by NIR and visible light patterns.  We demonstrate that electrical and natural VEPs summed linearly in the visual cortex, and both responses decreased under brighter ambient light. Responses to visible light flashes increased over 3 orders of magnitude of contrast (flash/background), while for electrical stimulation the contrast range was limited to 1 order of magnitude. The maximum amplitude of the prosthetic VEP was three times lower than the maximum response to a visible flash over the same area on the retina.  Ambient light affects prosthetic responses, albeit much less than responses to visible stimuli. Prosthetic representation of contrast in the visual scene can be encoded, to a limited extent, by the appropriately calibrated stimulus intensity, which also depends on the ambient light conditions. Such calibration will be important for patients combining central prosthetic vision with natural peripheral sight, such as in age-related macular degeneration

The Future of the Operating Room: Surgical Preplanning and Navigation using High Accuracy Ultra-Wideband Positioning and Advanced Bone Measurement

This dissertation embodies the diversity and creativity of my research, of which much has been peer-reviewed, published in archival quality journals, and presented nationally and internationally. Portions of the work described herein have been published in the fields of image processing, forensic anthropology, physical anthropology, biomedical engineering, clinical orthopedics, and microwave engineering. The problem studied is primarily that of developing the tools and technologies for a next-generation surgical navigation system. The discussion focuses on the underlying technologies of a novel microwave positioning subsystem and a bone analysis subsystem. The methodologies behind each of these technologies are presented in the context of the overall system with the salient results helping to elucidate the difficult facets of the problem. The microwave positioning system is currently the highest accuracy wireless ultra-wideband positioning system that can be found in the literature. The challenges in producing a system with these capabilities are many, and the research and development in solving these problems should further the art of high accuracy pulse-based positioning

Biomechanics of transapical mitral valve implantation

2014 Summer.Includes bibliographical references.Heart disease is the number one killer in the United States. Within this sector, valve disease plays a very important role: Approximately 6% of the entire population has either prolapse or stenosis of the mitral valve and this percentage only increases when looking only at the elderly population. Transapical mitral valve implantation has promised to be a potential therapy for high-risk patients presenting with MR; however it is unclear what the best method of securing a valve within the mitral annulus may be to provide a safe and efficient valve replacement. The objective of this research is to study and understand the underlying biomechanics of fixation of transapical mitral valves within the native mitral annulus. Two different transapical mitral valve prosthesis designs were tested: One valve design has a portion of the leaflets atrialized such that it has a shorter stent height and the valve itself sits within the native annulus, the other design is not atrialized and protrudes further into the left ventricle. The valves were implanted in a left heart simulator to assess leaflet kinematics and hemodynamics using high speed imagery and particle image velocimetry techniques. An in vitro passive beating heart model was then used to assess the two different fixation methods (namely, anchored at the apex vs. anchored at the annulus) with respect to paravalvular regurgitation. Leaflet kinematics and hemodynamics revealed proper leaflet coaptation and acceptable pressure gradients and inflow fillings; however, both designs yielded elevated turbulence stresses within the ventricle. At 60 beats per minute, leaflet opening and closing times were both under 0.1 seconds, max Reynolds shear stresses were between 40 and 60 N/m2 and maximum velocities were approximately 1.4 m/s. Assessment of the different fixation methods during implantation revealed the superiority of the atrialized valve when anchored at the annulus (p<0.05), but showed no such comparison during tethered implantation. In addition to the results of statistical testing, observations show that the importance of the relationship between ventricular stent height and fixation method compared with native anatomy plays an important role in overall prosthesis function regardless of implantation method

Rhythmic Action Synchronizes Memory Replay During Reinforcement Learning

Our cognitive abilities - learning from the past, sensing the current environment, planning into the future, executing an action, and infusing value into an experience - all rely on precisely timed and widespread electrical communications across neural networks. The brain’s hippocampal formation receives multimodal input, forges episodic associations, and predicts future state. Oscillating electrical bursts originating from the hippocampus, termed ‘sharp-wave ripples’ (SWR), often contain patterns of previously expressed neural spike sequences, and are necessary for certain forms of learning and memory. The discharge of SWR-replay resonates in remote parts of the brain and displays specific characteristics depending on a subject’s state of awareness and sensory context. In the sleep state, when motoric repertoire is limited, waves of breathing synchronize neural activity in several regions of the brain, including SWRs of the hippocampus. During active sensation of the awake state, cyclic licking dynamically entrains taste-reward networks in subcortical and cortical areas throughout learning. However, the neural correlates linking oromotor movements in the active learning state to the memory system of the hippocampal formation have not yet been established. Given the recurrence of SWR-replay during rhythmic ingestion of reinforcement learning and the hierarchical coupling of orofacial behaviors, we hypothesized that repeated licking could provide the oscillatory framework to synchronize memory reactivation during active learning. We approach this question with new technology development to track licking events at a reward port (P-event) during behavior on a spatial alternation task. Additionally, we developed a modular brain implant to simultaneously record from hippocampal area CA1 and medial entorhinal cortex (MEC) - interconnected brain regions that are crucial to episodic memory processing. Along with the co-modulation of individual neurons by licking and SWRs, we provide the first evidence that SWRs detected in dorsal CA1 synchronize with the phase of P-event cycle during learning. Furthermore, we confirmed that SWRs occurring during licking bouts contain neural reactivation of active navigation and trigger enhanced ripple-frequency power in downstream MEC. These results connect movement with memory and may assist in addressing abnormal ingestion behaviors that negatively affect mental or physical healt

Use of ASSR in estimation of hearing thresholds for cochlear implant users

Sisäkorvaistute on osittain kirurgisella toimenpiteellä korvaan asetettu elektroninen laite. Sen avulla ohitetaan vahingoittunut sisäkorva ja voidaan tuottaa kuurolle tai vakavasti kuulovammaiselle henkilölle ääniaistimuksia. Se tuottaa sähköisen ärsykkeen, joka ohittaa vahingoittuneet tai puuttuvat simpukan karvasolut ja stimuloi suoraan kuulohermoja. Kuulon testaus perinteisillä menetelmillä perustuu potilaan antamaan subjektiiviseen palautteeseen. Lapsilta ja vaikeasti testattavilta potilailta tällaisen palautteen saaminen on mahdotonta. Kuulon mittaus ilman potilaan aktiivista osallistumista ja yhteistyötä on mahdollista objektiivisia kuulonmittausmenetelmiä käyttäen. Objektiivisten kuulonmittausmenetelmien tarve on kasvanut maailmanlaajuisen vastasyntyneiden kuulon tutkimuksen myötä. Auditory steady-state response (ASSR) on uusi tutkimusmenetelmä, jolla voidaan mitata ääniärsykkeen tuottamia aivorunko- tai kortikaalivasteita. Sen avulla on mahdollista objektiivisesti arvioida potilaan kuulokynnys taajuusspesifisti. ASSR:n avulla ärsykkeet voidaan antaa suoraan sisäkorvaistutteen kautta, joka mahdollistaa sisäkorvaistutepotilaiden objektiivisen kuulonmittauksen. Tämän tutkimuksen tarkoituksena oli tutkia ASSR-vasteita sisäkorvaistutepotilailta ja selvittää voiko näitä vasteita käyttää apuna lasten ja vaikeasti testattavien potilaiden istutteen säätämisessä. Tutkimuksen tulokset viittaavat vahvasti siihen, että sisäkorvaistutteen kautta stimuloituja ASSR-vasteiden parametreja voidaan käyttää potilaan audiogrammin estimointiin. Jatkotutkimuksien myötä voi olla mahdollista, että niitä voidaan käyttää hyväksi sisäkorvaistutteen prosessorin parametrien ohjelmoinnissa.A cochlear implant is a surgically implanted electronic device that bypasses damaged inner ear and provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. It produces an electrical stimulus, which bypasses the damaged or missing hair cells and stimulates the remaining auditory neurons directly. Hearing testing by traditional methods is subjective and is based on the sound perception that patient reports. From children or difficult-to-test patients this kind of feedback is not possible to receive. To define the patient's hearing ability without active participation or cooperation, objective hearing tests can be applied. Since the worldwide introduction of hearing screening in newborns, the need for objective audiometric techniques to quantify hearing thresholds has increased. Auditory steady state response (ASSR) is a new research method for determining brainstem or cortical responses caused by sound stimuli. With the ASSR method it may be possible to record responses elicited by sound stimuli given through the cochlear implant. This could offer an opportunity to objectively determine an implanted patient's hearing threshold. The purpose of this research was to study ASSR responses with cochlear implant patients and to determine how ASSR can help in programming implant processor with difficult-to-test patients and children who cannot report their auditory perception. The results of this study strongly suggest that ASSR parameters measured using stimulation through cochlear implant can be used in estimation of patient's audiogram. With further study it might be used in determining the parameters for the programming of the implant processor