Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 111.738
Filtrar
Mais filtros

Assunto principal
Tipo de estudo
Idioma
Intervalo de ano de publicação
1.
Nat Commun ; 11(1): 5073, 2020 10 08.
Artigo em Inglês | MEDLINE | ID: mdl-33033238

##### RESUMO

Brain cells continuously produce and release protons into the extracellular space, with the rate of acid production corresponding to the levels of neuronal activity and metabolism. Efficient buffering and removal of excess H+ is essential for brain function, not least because all the electrogenic and biochemical machinery of synaptic transmission is highly sensitive to changes in pH. Here, we describe an astroglial mechanism that contributes to the protection of the brain milieu from acidification. In vivo and in vitro experiments conducted in rodent models show that at least one third of all astrocytes release bicarbonate to buffer extracellular H+ loads associated with increases in neuronal activity. The underlying signalling mechanism involves activity-dependent release of ATP triggering bicarbonate secretion by astrocytes via activation of metabotropic P2Y1 receptors, recruitment of phospholipase C, release of Ca2+ from the internal stores, and facilitated outward HCO3- transport by the electrogenic sodium bicarbonate cotransporter 1, NBCe1. These results show that astrocytes maintain local brain extracellular pH homeostasis via a neuronal activity-dependent release of bicarbonate. The data provide evidence of another important metabolic housekeeping function of these glial cells.

##### Assuntos
Astrócitos/metabolismo , Bicarbonatos/metabolismo , Encéfalo/metabolismo , Espaço Extracelular/metabolismo , Acetazolamida/farmacologia , Trifosfato de Adenosina/metabolismo , Animais , Astrócitos/efeitos dos fármacos , Anidrases Carbônicas/metabolismo , Células Cultivadas , Estimulação Elétrica , Fluorescência , Hipocampo/metabolismo , Concentração de Íons de Hidrogênio , Camundongos Endogâmicos C57BL , Modelos Biológicos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Antagonistas Purinérgicos/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos Sprague-Dawley , Receptores Purinérgicos/metabolismo , Transdução de Sinais , Simportadores de Sódio-Bicarbonato/metabolismo
2.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3751-3754, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018817

##### RESUMO

The aging process, as well as neurological disorders, causes a decline in sensorimotor functions, which can often bring degraded motor output. As a means of compensation for such sensorimotor deficiencies, sensorimotor augmentation has been actively investigated. Consequently, exoskeleton devices or functional electrical stimulation could augment the muscle activity, while textured surfaces or electrical nerve stimulations could augment the sensory feedback. However, it is not easy to precisely anticipate the effects of specific augmentation because sensory feedback and motor output interact with each other as a closed-loop operation via the central and peripheral nervous systems. A computational internal model can play a crucial role in anticipating such an effect of augmentation therapy on the motor outcome. Still, no existing internal sensorimotor loop model has been represented in a complete computational form facilitating the anticipation. This paper presents such a computational internal model, including numerical values representing the effect of sensorimotor augmentation. With the existing experimental results, the model performance was evaluated indirectly. The change of sensory gain affects motor output inversely, while the change of motor gain did not change or minimally affects the motor output.Clinical Relevance- The presented computational internal model will provide a simple and easy tool for clinicians to design therapeutic intervention using sensorimotor augmentation.

##### Assuntos
Retroalimentação Sensorial , Sensação , Estimulação Elétrica
3.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3823-3826, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018834

##### RESUMO

the purpose of targeted muscle reinnervation (TMR) surgery is to provide more electromyography information for prosthetic control by reconstructing the deconstructed structure between the distal nerve and the stump muscle. Functional electrical stimulation (FES) of denervated muscles or proximal nerve stump after peripheral nerve surgery can effectively promote nerve regeneration and muscle function recovery. This pilot divided SD adult male rats into normal control group, denervation group, TMR group, and FES group according to whether they received TMR surgery and whether they received FES after surgery. The results showed that low-frequency electrical stimulation treatment could effectively promote transplanted nerve regeneration and significantly enhances motor function of target muscles.Clinical Relevance-This experiment successfully established TMR rat models, and explored the recovery of injured neuromuscular function by using electrodes implanted intramuscularly and analyzing myoelectric signals, and the use of low-frequency electrical stimulation treatment had a positive effect on the regeneration of the transplanted nerve.

##### Assuntos
Fenômenos Fisiológicos Musculoesqueléticos , Procedimentos Cirúrgicos Reconstrutivos , Animais , Estimulação Elétrica , Masculino , Regeneração Nervosa , Procedimentos Neurocirúrgicos , Ratos
4.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3909-3912, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018855

##### RESUMO

Haptic feedback allows an individual to identify various object properties. In this preliminary study, we determined the performance of stiffness recognition using transcutaneous nerve stimulation when a prosthetic hand was moved passively or was controlled actively by the subjects. Using a 2x8 electrode grid placed along the subject's upper arm, electrical stimulation was delivered to evoke somatotopic sensation along their index finger. Stimulation intensity, i.e. sensation strength, was modulated using the fingertip forces from a sensorized prosthetic hand. Object stiffness was encoded based on the rate of change of the evoked sensation as the prosthesis grasped one of three objects of different stiffness levels. During active control, sensation was modulated in real time as recorded forces were converted to stimulation amplitudes. During passive control, prerecorded force traces were randomly selected from a pool. Our results showed that the accuracy of object stiffness recognition was similar in both active and passive conditions. A slightly lower accuracy was observed during active control in one subject, which indicated that the sensorimotor integration processes could affect haptic perception for some users.

##### Assuntos
Membros Artificiais , Estimulação Elétrica Nervosa Transcutânea , Braço , Estimulação Elétrica , Mãos
5.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 4126-4129, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018906

##### RESUMO

A surface electromyography (sEMG) detector, that not only removes stimulation artifacts entirely but also increases the recording time, has been developed in this paper. The sEMG detector consists of an sEMG detection circuit and a stimulation isolator. The sEMG detection circuit employs a stimulus isolate switch (SIS), a blanking (BLK) and non-linear feed-back (NFB) circuit to remove the artifacts and to increase the recording time. In the SIS, the connection between stimulator and stimulation electrodes, along with the stimulation electrodes and the ground are controlled by an opto-isolator, and the connection of instrument amplifier and the recording electrodes are controlled by CMOS-based switches. The mode switches of the BLK and the NFB circuit also employs CMOS-based switches. By an accurate timing adjustment, the voluntary EMG can be recorded during electrical stimulation. Two 6 able-bodied experiments have been performed to test the three anti-artifact sEMG detector: BLK, BLK&SIS, BLK&SIS&NFB. The results indicate that the BLK&SIS&NFB proposed in this work effectively removes stimulus artifacts and M-waves, and has a longer recording time compared with BLK and BLK&SIS circuits.

##### Assuntos
Amplificadores Eletrônicos , Artefatos , Estimulação Elétrica , Eletrodos , Eletromiografia
6.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 5208-5211, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019158

##### RESUMO

The "diving reflex" (DR) is a very powerful autonomic reflex that facilitates survival in hypoxic/anoxic conditions and could trigger multifaceted physiologic effects for the treatment of various diseases by modulating the cardiovascular, respiratory, and nervous systems. The DR can be induced by cold water or noxious gases applied to the anterior nasal mucosa and paranasal regions, which can stimulate trigeminal thermo- or chemo-receptors to send afferent signals to medullary nuclei which mediate the sympathetic and parasympathetic nervous systems. Although promising, these approaches have yet to be adopted in routine clinical practice due to the inability to precisely control exposure-response relationships, lack of reproducibility, and difficulty implementing in a clinical setting. In this study, we present the ability of electrical Trigeminal (Infraorbital) Nerve Stimulation (eTINS) to induce the DR in a dose-controllable manner. We found that eTINS not only triggered specific physiological changes compatible with the pattern of "classic" DR observed in animals/humans, but also controlled the induced-DR at varying levels. This study demonstrates, for the first time, that the intensity of the DR is controllable by dose and opens possibility to investigate its protective mechanism against various pathologies in well-controlled research settings.

##### Assuntos
Reflexo de Mergulho , Animais , Estimulação Elétrica , Humanos , Nervo Maxilar , Reflexo , Reprodutibilidade dos Testes
7.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 5216-5219, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019160

##### RESUMO

Vagus nerve stimulation (VNS) administered to individuals following events such as severe trauma can be a potential therapy to attenuate gut injury and its sequelae. To determine the effective dose of transcutaneous electrical VNS (TE-VNS) and explore an effective method for performing TE-VNS, a measurement system was developed for the detection of vagus nerve response to TE-VNS. In addition, a noise-suppressed transcutaneous electrical stimulator (TES) was constructed for the same purpose. Using these tools, waveforms considered as nerve action potentials were successfully recorded. The recorded waveforms were similar to those evoked by direct electrical stimulation as reported in a latest publication. Our recorded waveforms also varied according to the pulse width of electrical stimulation, indicating the future possibility of determining the potential TES dose.Clinical Relevance- This is a basic research for application to acute therapy of systemic inflammatory response syndrome (SIRS) by transcutaneous electrical stimulation of the vagus nerve.

##### Assuntos
Estimulação Elétrica Nervosa Transcutânea , Estimulação do Nervo Vago , Animais , Meato Acústico Externo , Estimulação Elétrica , Humanos , Ratos , Nervo Vago
8.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 5220-5223, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33019161

##### RESUMO

The aim of this study is to design an implantable Lower Esophageal Sphincter (LES) stimulator connected and controlled by an Android Bluetooth for the treatment of the gastroesophageal reflux disease (GERD). Then the animal experiments are carried out to evaluate the function of the system. The LES stimulator is composed of an external controller, an Android application (APP) via a smart phone and an implantable electronic device (IED). The external controller is designed to receive the settings parameters information sent by the Android APP via a Bluetooth module, and then is programmed to generate specific electrical stimulation pulses to the LES. The Android APP controls the start and stop of stimulation and the settings of stimulation parameters. The in vivo IED consists of a bipolar stimulating lead, a bipolar head connector and a receiving module. The bipolar stimulating lead is constructed of biocompatible materials: platinum-iridium electrodes which are coated with parylene and an outer silicone rubber sheathing. The size of the receiving module has been significantly decreased to 20×20×2 mm3, which is packaged by polydimethylsiloxane (PDMS) and proposed to deliver stimulation pulses from the external controller to the implantable lead. The one-month implantation experiment on rabbits has been performed to evaluate the LES stimulator. The results indicate that the proposed LES stimulator meets the requirements of the functions, effectiveness and safety.

##### Assuntos
Terapia por Estimulação Elétrica , Refluxo Gastroesofágico , Animais , Estimulação Elétrica , Esfíncter Esofágico Inferior , Refluxo Gastroesofágico/terapia , Próteses e Implantes , Coelhos
9.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2324-2327, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018473

##### RESUMO

Existing computational studies of cochlear implants have demonstrated that the structural detail of threedimensional (3D) cochlear models exerts influence on the current spread within the cochlea. Nevertheless, the significance of including the microstructures inside the modiolar bone in a cochlear model is still unclear in the literature. We employed two different multi-compartment neuron models to simulate auditory nerve fibres, and compared response characteristics of the fibre population between a detailed and a simplified 3D cochlear model. Results showed that although the prediction of firing is dependent on the details of the neuron model, the responses of the fibre population to the electrical stimulus, especially the location of the initiation of action potential, varied between the detailed and the simplified models. Therefore, the inclusion of the modiolar microstructures in a cochlear model may be necessary for fully understanding the firing of auditory nerve fibres.

##### Assuntos
Implantes Cocleares , Nervo Coclear , Cóclea , Estimulação Elétrica , Fibras Nervosas
10.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2442-2446, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018500

##### RESUMO

Galvanic vestibular stimulation (GVS) involves the application of electrical current through electrodes placed exclusively at the mastoids or in combination with electrodes placed on other regions. It is a simple, safe modality to modulate and probe vestibular function. Despite a long history of use, it continues to be primarily used as a research tool with no fully developed therapeutic use. This is partly due to the fact that to further advance this technique, a better understanding of what structures are stimulated and by how much is needed. While models have been proposed to explain response, cellular and structural substrates confirmed empirically, the exact current flow pattern has not been investigated.The goal of this study is to therefore determine current flow patterns in GVS. In order to do so, we developed the first ultrahigh-resolution finite element model of GVS incorporating the tiny structures of interest in the inner ear. We simulated the Bilateral-Bipolar, Bilateral-Monopolar, and the Unilateral-Monopolar configurations. Specifically, we generated surface electric field magnitude plots for the brain and for structures considered most relevant to GVS mechanism of action- the semi-circular canals (SCC) and the otolith.Findings show that the Bilateral-Bipolar configuration results in the most spatially restricted flow while the Unilateral-Monopolar configuration results in the most diffuse. With respect to SCC and the otolith, both Bilateral-Bipolar and Bilateral-Monopolar configurations led to similar flow in both the left and right pairs. For the Unilateral-Monopolar configuration, we observed increased flow in the left pair.We expect via this first model developed for GVS, researchers investigating this technique to have a better understanding of the effects of different configurations. Anatomically detailed models like these may also help understand the mechanism of action and may guide the rational design of future GVS administration.

##### Assuntos
Sensação , Vestíbulo do Labirinto , Encéfalo , Estimulação Elétrica , Membrana dos Otólitos
11.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2479-2482, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018509

##### RESUMO

To build hippocampal memory prosthesis for restoring memory functions, we previously developed and implemented a multi-input multi-output (MIMO) nonlinear dynamic model of the hippocampus. This model can successfully predict hippocampal output spike activities based on input spike activities, and thus be used to drive microstimulation to bypass the damaged hippocampal region. Building such a MIMO model involves estimations of a large number of model coefficients, which typically takes hundreds of hours using a single personal computer. In practice, however, due to the requirement of medical care and clinical trials, the modeling processes must be completed within 72 hours after the recording, so that models can be used to drive stimulations. To solve this problem, we utilized a parallelization strategy to divide the whole MIMO model computation involving iterative estimation and optimization into independent computing tasks that can be performed simultaneously in multiple computer nodes. Such a strategy was implemented on the high-performance computing cluster at the University of Southern California. It reduced the model estimation time to tens of hours and thus allowed us to complete the modeling process within the required time frame to further test model-driven electrical stimulation for the hippocampal memory prosthesis.

##### Assuntos
Hipocampo , Memória , Estimulação Elétrica , Microcomputadores , Dinâmica não Linear
12.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2524-2527, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018520

##### RESUMO

Surgical resection of the seizure onset zone (SOZ) could potentially lead to seizure-freedom in medically refractory epilepsy patients. However, localizing the SOZ can be a time consuming and tedious process involving visual inspection of intracranial electroencephalographic (iEEG) recordings captured during passive patient monitoring. Single pulse electrical stimulation (SPES) is currently performed on patients undergoing invasive EEG monitoring for the main purposes of mapping functional brain networks such as language and motor networks. We hypothesize that evoked responses from SPES can also be used to localize the SOZ as they may express the natural frequencies and connectivity of the iEEG network. To test our hypothesis, we construct patient specific single-input multi-output transfer function models from the evoked responses recorded from five epilepsy patients that underwent SPES evaluation and iEEG monitoring. Our preliminary results suggest that the stimulation electrodes that produced the highest gain transfer functions, as measured by the ${\mathcal{H}_\infty }$ norm, correspond to those electrodes clinically defined in the SOZ in successfully treated patients.Clinical Relevance- This study creates an innovative tool that allows clinicians to identify the seizure onset zone in medically refractory epilepsy patients using quantitative metrics thereby increasing surgical success outcomes, mitigating patient risks, and decreasing costs.

##### Assuntos
Epilepsia Resistente a Medicamentos , Epilepsia , Epilepsia Resistente a Medicamentos/terapia , Estimulação Elétrica , Eletrocorticografia , Epilepsia/terapia , Humanos , Convulsões/terapia
13.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2881-2884, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018608

##### RESUMO

Lack of sensory feedback is one of the main issues contributing to lack of control and embodiment for upper-limb prostheses. Noninvasive nerve stimulation may help amputees overcome such limitations by providing a degree of somatotopic feedback, however its neural correlates have been only partly characterized so far. While the effects of median nerve stimulation have been studied, little attention has been given to ulnar nerve and bipolar stimulation, which might provide a finer modulation of the somatotopic sensation. Here, monopolar and bipolar transcutaneous electrical nerve stimulation (TENS) is repeatedly applied to the ulnar and median nerves and elicited Somatosensory Evoked Potentials (SEPs) are characterized by means of electroencephalography (EEG). Clear P50, P150 and P270 SEPs were outlined, with significantly different amplitudes between configurations. In each case scalp topographies showed a strong contralateral activation in the early phase after the stimulus onset (40-100 ms), compatible with generators in the somatosensory cortex and in accordance to previous literature on actual tactile stimuli, which gives way to a frontal-central distribution at long latencies (130-190 ms). These findings, although needing further validation with a larger pool of subjects, show that bipolar TENS could have potential applications in improving prosthesis control with tactile feedback.

##### Assuntos
Potenciais Somatossensoriais Evocados , Córtex Somatossensorial , Estimulação Elétrica , Nervo Mediano , Extremidade Superior
14.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2929-2933, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018620

##### RESUMO

Pulsatile electrical stimulation is used in neural prostheses such as the vestibular prosthesis. In a healthy vestibular system, head motion is encoded by changes in the firing rates of afferents around their spontaneous baseline rate. For people suffering from bilateral vestibular disorder (BVD), head motion no longer modulates firing rate. Vestibular prostheses use a gyroscope to detect head motion and stimulate neurons directly in a way that mimics natural modulation. Proper restoration of vestibular function relies on the ability of stimulation to evoke the same firing patterns as the healthy system. For this reason, it is necessary to understand what firing rates are produced for different stimulation parameters. Two stimulation parameters commonly controlled in pulsatile neuromodulation are pulse rate and pulse amplitude. Previous neural recording experiments in the vestibular nerve contradict widely held assumptions about the relationship between pulse rates and evoked spike activity, and the relationship between pulse amplitude and neural activity has not been explored. Here we use a well-established computational model of the vestibular afferent to simulate responses to different pulse rates and amplitudes. We confirm that our simulated neural results agree with the existing experimental data. Finally, we developed the "Action Potential Collision" (APC) equation that defines induced firing as a function of spontaneous firing rate, pulse rate, and pulse amplitude. We show that this relationship can successfully predict simulated vestibular activity by accounting for interactions between pulses and spontaneous firing.

##### Assuntos
Próteses Neurais , Doenças Vestibulares , Vestíbulo do Labirinto , Estimulação Elétrica , Humanos , Nervo Vestibular
15.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2934-2937, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018621

##### RESUMO

Bioelectronic neural interfaces that deliver adaptive therapeutic stimulation in an intelligent manner must be able to sense and stimulate activity within the same nerve. Existing minimally-invasive peripheral neural interfaces can provide a read-out of the aggregate level of activity via electrical recordings of nerve activity, but these recordings are limited in terms of their specificity. Computational simulations can provide fine-grained insight into the contributions of different neural populations to the extracellular recording, but integration of the signals from individual nerve fibers requires knowledge of spread of current in the complex (heterogenous, anisotropic) extracellular space. We have developed a model which uses the open-source EIDORS package for extracellular stimulation and recording in the pelvic nerve. The pelvic nerve is the primary source of autonomic innervation to the pelvic organs, and a prime target for electrical stimulation to treat a variety of voiding disorders. We simulated recordings of spontaneous and electrically-evoked activity using biophysical models for myelinated and unmyelinated axons. As expected, stimulus thresholds depended strongly on both fibre type and electrode-fibre distance. In conclusion, EIDORS can be used to accurately simulate extracellular recording in complex, heterogenous neural geometries.

##### Assuntos
Axônios , Nervos Periféricos , Estimulação Elétrica , Eletrodos , Fibras Nervosas
16.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2938-2941, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018622

##### RESUMO

Electrical brain stimulation (EBS) has been actively researched because of its clinical application and usefulness in brain research. However, its effect on individual neurons remains uncertain, as each neuron's response to EBS is highly variable and dependent on its morphology and the axis in which a neuron lies. Hence, our goal was to investigate the way that neuronal morphology affects the cellular response to extracellular stimulation from multiple directions. In this computational study, we observed that the varying neuronal morphology and direction of applied electrical field (EF) had some influence on the excitation threshold, which generates an action potential. Further, change of the excitation threshold depending on EF directions was observed.Clinical Relevance- These findings would help us to understand the variability in the modulatory effects of EBS at the cellular level and would be the basis for understanding the packed fibers' responses to EBS. Ultimately, considering EBS' clinical application, it may also help to predict patient's results from EBS treatment.

##### Assuntos
Modelos Neurológicos , Neurônios , Encéfalo , Estimulação Elétrica , Eletricidade , Humanos
17.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3393-3398, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018732

##### RESUMO

Electrical stimulation of surviving retinal neurons has proven effective in restoring sight to totally blind patients affected by retinal degenerative diseases. Morphological and biophysical differences among retinal ganglion cells (RGCs) are important factors affecting their response to epiretinal electrical stimulation. Although detailed models of ON and OFF RGCs have already been investigated, here we developed morphologically and biophysically realistic computational models of two classified RGCs, D1-bistratified and A2-monostratified, and analyzed their response to alternations in stimulation frequency (up to 200 Hz). Results show that the D1-bistratified cell is more responsive to high frequency stimulation compared to the A2-monostratified cell. This differential RGCs response suggests a potential avenue for selective activation, and in turn different encoded percept of RGCs.

##### Assuntos
Degeneração Retiniana , Células Ganglionares da Retina , Estimulação Elétrica , Humanos , Retina
18.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3521-3524, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018763

##### RESUMO

Cortical visual prostheses could one day help restore sight to the blind by targeting the visual cortex with electrical stimulation. However, power consumption and limited spatial resolution impose limits on performance, while large amounts of electrical charge sometimes necessary to evoke phosphenes can cause seizures. Here, we propose the use of the local field potential as a control signal for the timing of stimulation to reduce charge requirements. In Sprague-Dawley rats, visual cortex was electrically stimulated at random times, and neural responses recorded. Electrical stimulation at specific phases of the local field potential required smaller amounts of charge to elicit spikes than naïve stimulation. Incorporating this into prosthesis design could improve their safety and efficacy.

##### Assuntos
Potenciais Evocados Visuais , Córtex Visual , Animais , Estimulação Elétrica , Fosfenos , Ratos , Ratos Sprague-Dawley
19.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3529-3532, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018765

##### RESUMO

Retinal microprostheses strive to evoke a sense of vision in individuals blinded by outer retinal degenerative diseases, by electrically stimulating the surviving retina. It is widely suspected that a stimulation strategy that can selectively activate different retinal ganglion cell types will improve the quality of evoked phosphenes. Previous efforts towards this goal demonstrated the potential for selective ON and OFF brisk-transient cell activation using high-rate (2000 pulses per second, PPS) stimulation. Here, we build upon this earlier work by testing an additional rate of stimulation and additional cell populations. We find considerable variability in responses both within and across individual cell types, but show that the sensitivity of a ganglion cell to repetitive stimulation is highly correlated to its single-pulse threshold. Consistent with this, we found thresholds for both stimuli to be correlated to soma size, and thus likely mediated by the properties of the axon initial segment. The ultimate efficacy of high-rate stimulation will likely depend on several factors, chief among which are (a) the residual ganglion types, and (b) the stimulation frequency.

##### Assuntos
Degeneração Retiniana , Células Ganglionares da Retina , Potenciais de Ação , Estimulação Elétrica , Humanos , Retina
20.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 3533-3536, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018766

##### RESUMO

Microelectronic retinal prostheses electrically stimulate retinal neurons with the goal of restoring vision in patients blinded by outer retinal degeneration. Despite some success in clinical trials, the quality of vision elicited by these devices is still limited. To improve the performance of retinal prostheses, our group studied how retinal neurons respond to electric stimulation. Our previous work showed that responses of retinal ganglion cells (RGCs) are frequency-dependent and different types of RGCs can be preferentially activated with a specific frequency and current amplitude. In the present study, we systemically examined responses of RGCs to sinusoidal electric stimulation with varying frequencies and amplitudes. We found that ON sustained alpha RGCs show distinct stimulus-response relationships to low and high frequency stimulation. For example, RGCs showed monotonic response curves to 500 Hz sinusoidal stimulation, whereas they showed non-monotonic response curves to 2000 Hz stimulation. We also described how increasing stimulus frequency gradually changed the response curves of RGCs.

##### Assuntos
Degeneração Retiniana , Próteses Visuais , Potenciais de Ação , Estimulação Elétrica , Humanos , Células Ganglionares da Retina