Browsing by Author "Stoddart, Paul"

Now showing 1 - 5 of 5
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    Biological Considerations of Optical Interfaces for Neuromodulation
    (WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019-07) Hart, William; Kameneva, Tatiana; Wise, Andrew; Stoddart, Paul
    The success of devices such as cochlear implants and pacemakers has led to increasing interest in new applications of artificial neural interfaces, ranging from brain–computer interfaces to vagus nerve stimulators. Both the established and emerging applications of neural interfaces have highlighted the need for improvements in spatial selectivity and reduced invasiveness, which in turn has driven growing interest in optical interfaces. The delivery of light to—and collection of light from—neural tissue presents distinct challenges for optical devices. This review presents the status of optical interface technologies with a focus on biological considerations, such as biocompatibility, thermal loading, and tissue response. Attention is also paid to factors affecting the portability of optical interfaces, and issues around reliability and manufacturing that need to be considered for successful translation. Indeed, it is imperative that engineers work closely with physiologists, clinicians, and patients when developing devices for research and the clinic. Finally, emerging trends and the potential for new technologies to disrupt the field are discussed. While many engineering challenges remain to be overcome, the achievements to date suggest that optical neuromodulation techniques have significant potential to be deployed in future for a wide range of practical therapeutic applications.
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    Combined optogenetic and electrical stimulation of auditory neurons increases effective stimulation frequency—an in vitro study
    (IOP Publishing, 2020-01) Hart, William; Richardson, Rachael; Kameneva, Tatiana; Thompson, Alex; Wise, Andrew; Fallon, James; Stoddart, Paul; Needham, Karina
    OBJECTIVE: The performance of neuroprostheses, including cochlear and retinal implants, is currently constrained by the spatial resolution of electrical stimulation. Optogenetics has improved the spatial control of neurons in vivo but lacks the fast-temporal dynamics required for auditory and retinal signalling. The objective of this study is to demonstrate that combining optical and electrical stimulation in vitro could address some of the limitations associated with each of the stimulus modes when used independently. APPROACH: The response of murine auditory neurons expressing ChR2-H134 to combined optical and electrical stimulation was characterised using whole cell patch clamp electrophysiology. MAIN RESULTS: Optogenetic costimulation produces a three-fold increase in peak firing rate compared to optical stimulation alone and allows spikes to be evoked by combined subthreshold optical and electrical inputs. Subthreshold optical depolarisation also facilitated spiking in auditory neurons for periods of up to 30 ms without evidence of wide-scale Na+ inactivation. Significance These findings may contribute to the development of spatially and temporally selective optogenetic-based neuroprosthetics and complement recent developments in "fast opsins".
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    Effect of embedded optical fibres on the mechanical properties of cochlear electrode arrays
    (Elsevier Ltd., 2016-02) Carland, Emma; Stoddart, Paul; Cadusch, Peter; Fallon, James; Wade, Scott
    Incorporating optical fibres in cochlear electrode arrays has been proposed to provide sensors to help minimise insertion trauma and also for the delivery of light in optical nerve stimulation applications. However, embedding an optical fibre into an electrode array may change its stiffness properties, which can affect the level of trauma during insertion. This report uses measurements of buckling and deflection force to compare the stiffness properties of a range of cochlear electrode arrays (Nucleus straight array, rat array, cat array and guinea pig array) with custom arrays containing an embedded optical fibre. The cladding diameters of the optical fibres tested were 125 µm, 80 µm and 50 µm. The results show that the stiffness of the optical-fibre-embedded arrays is related to the diameter of the optical fibre. Comparison with wired arrays suggests optical fibres with a diameter of 50 µm could be embedded into an electrode array without significantly changing the stiffness properties of the array
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    Measurement of forces at the tip of a cochlear implant during insertion.
    (IEEE, 2014-01-02) Wade, Scott; Fallon, James; Wise, Andrew; Shepherd, Robert; James, Natalie; Stoddart, Paul
    An optical fiber based sensor has been developed to measure the forces at the tip of an electrode array during insertion into the cochlea. The sensor, utilizing optical fiber Bragg grating technology, was incorporated into a custom designed Pt-banded electrode array for guinea pigs. In vivo experiments were undertaken in which forces at the tip of the array were measured in real time during the insertion. Data was obtained for maximum insertion forces of up to 254 mN. Histology was performed on the excised cochleae with the sensors fixed in position to evaluate the level of insertion trauma. The insertion experiments demonstrated a clear correlation between applied force and collateral tissue damage.
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    Thermal damage threshold of neurons during infrared stimulation
    (Biomedical Optics Express, 2020-04) Brown, William; Needham, Karina; Begeng, James; Thompson, Alexander; Nayagam, Bryony; Kameneva, Tatiana; Stoddart, Paul
    In infrared neural stimulation (INS), laser-evoked thermal transients are used to generate small depolarising currents in neurons. The laser exposure poses a moderate risk of thermal damage to the target neuron. Indeed, exogenous methods of neural stimulation often place the target neurons under stressful non-physiological conditions, which can hinder ordinary neuronal function and hasten cell death. Therefore, quantifying the exposure-dependent probability of neuronal damage is essential for identifying safe operating limits of INS and other interventions for therapeutic and prosthetic use. Using patch-clamp recordings in isolated spiral ganglion neurons, we describe a method for determining the dose-dependent damage probabilities of individual neurons in response to both acute and cumulative infrared exposure parameters based on changes in injection current. The results identify a local thermal damage threshold at approximately 60 °C, which is in keeping with previous literature and supports the claim that damage during INS is a purely thermal phenomenon. In principle this method can be applied to any potentially injurious stimuli, allowing for the calculation of a wide range of dose-dependent neural damage probabilities. Unlike histological analyses, the technique is well-suited to quantifying gradual neuronal damage, and critical threshold behaviour is not required.