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1

Present and future of retinal implants

100%
Hottowy P.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
The retina is a key element of the visual system. The image captured by the eye is processed by the photoreceptors, specialized interneurons and finally by the ganglion cells that encode the visual information in sequences of the action potential and send this information to the brain. Some retinal diseases lead to loss of sight due to degeneration of the photoreceptors. However, the interneurons and the ganglion cells remain alive even in advanced stages of the disease, and keep the ability to process the visual information and send it out to the brain. Here comes the idea for visual prosthesis: replace the photoreceptors by a camera, deliver the visual information to the alive cells by stimulating them electrically, and it will propagate to the brain providing an artificial sight. The first generaion of the retinal prosthetic devices are already available for the patients. Unfortunately, one important limitation of current implants is low spatial resolution of the electrical stimulation. Large electrodes activate simultaneously large groups of neurons, what results in low resolution of the visual information. Furthermore, uncontrolled stimulation of different cell types makes it difficult for the brain to interpret the visual information, and unwanted stimulation of axons can further reduce the visual acuity. I will discuss design, performance and limitations of the current state-of-the-art prosthetic devices, as well as perspectives for development of next generation devices. I will also try to answer the following question: is it possible to build a retinal implant that could transfer to the brain visual information identical to that initiated in the healthy retina processing a complex visual scene? FINANCIAL SUPPORT: This work was supported by Polish National Science Centre grant DEC-2013/10/M/ NZ4/00268.
2

Modeling artifact in the living neural networks stimulating system

63%
Kolodziej K., Hottowy P.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Electrical stimulation of neurons results in large artifacts that makes recording of the stimulated activity difficult. In particular, detection of low‑latency spikes from directly activated neurons at the stimulating electrodes remains virtually impossible. AIM(S): We tested a new idea for artifact reduction, based on an optimized correction pulse (CP) applied to the stimulating electrode instantly after the stimulation pulse (SP). While being generated, the CP would induce the exact opposite of the artifact initiated by the SP. The signal distortion would be minimized, allowing for detection of the neuronal response during application of the CP. METHOD(S): Based on realistic model of the electrode impedance we estimated the shape of the stimulation artifact and calculated the optimal shape of the CP. We analyzed the hardware limitations of the stimulation circuit and its impact on the reduced artifact amplitude.We also considered the effects ofthe impedance model inaccuracy, as the real-life experiment will be based on impedance measurements with limited precision. We analyzed the artifact level at the output of the recording amplifierto take into accountits filtering properties. RESULTS: We analyzed the artifact reduction procedure for typical symmetric biphasic SP and impedance model for 5-micron platinium electrode. Even 2 microampere pulse without the CP generated the artifact that saturated the amplifier for at least 300 microseconds following the SP. Simulations confirmed that the optimal CP reduced the artifact almost completely. More importantly, even when electrode impedance was given with 5% error, the artifact was reduced more than 10 times for the first 300 microseconds after the SP, compared with the SP without correction. CONCLUSIONS: Numerical simulations suggest that our method will allow for reliable spikes recording even on the stimulating electrode. The experimental validation will take advantage of the novel stimulation/recording system currently being developed in our laboratory. FINANCIAL SUPPORT: This work was supported by Polish National Science Centre grant DEC-2013/10/M/ NZ4/00268.
3

Modular microelectronic system for in vivo electrical stimulation and recording at up to 512 electrodes

26%
Szypulska M., Wiacek P., Skoczen A., Fiutowski T., Ahmed I., Jedraczka M., Dusik J., Dwuznik M., Kublik E., Dabrowski W., Hottowy P.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Multielectrode silicon probes can record neuronal signals with combination of spatial and temporal resolution that other recording techniques cannot provide. Here we propose a novel microelectronic system that combines this functionality with advanced electrical stimulation. AIM(S): We designed a modular system for multielectrode electrical stimulation and recording in the brain of a living animal. It can be combined with any silicon probe used for brain research. It can generate complex sequences of stimulation pulses and simultaneously record at up to 512 electrodes. It can use up to 4 silicon probes in parallel, providing bidirectional communication with populations of neurons simultaneously in several brain areas. METHOD(S): The system is based on a dedicated multichannel CMOS chip. The chip includes 64 channels, digital circuitry for real-time communication with the control computer and a multiplexer that sends amplified signals from 64 electrodes into a single output line. The amplifier gain can be changed from 110 to 550. The low cut‑off frequency is set between 200 mHz and 3 Hz, the anti-aliasing filter is set at 7 kHz and the sampling rate is 40 kHz. The stimulation signal is controlled independently for each channel with 12-bit resolution and refresh rate of 40 kHz. Each amplifier can be disconnected from the electrode for the duration of the stimulation pulse for the artifact reduction. Up to 8 chips can be controlled in parallel with dedicated LabView software. RESULTS: Base version of the system was produced and tested with positive results. The final system is in the integration phase. We plan the first experiments to take place in the fall 2017 at the Nencki Institute for Experimental Biology. CONCLUSIONS: The reported system can generate complex sequences of stimulation pulses and record neuronal signals with very low artifacts at 512 electrodes, making it a powerful tool for mapping of the functional connections between brain circuits. FINANCIAL SUPPORT: Grant 2013/08/W/NZ4/00691, Polish National Science Centre.
4

Microelectronic system for low-artifact electrical stimulation and recording of brain activity at up to 512 electrodes

26%
Szypulska M., Wiacek P., Skoczen A., Ahmed I., Futowski T., Jurgielewicz P., Kolodziej K., Czerwinski M. B., Wojcik D. K., Mindur B., Kublik E., Dabrowski W., Hottowy P.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
|
nr Suppl.1
INTRODUCTION: We present a novel microelectronic system for in vivo stimulation and recording of neuronal activity. The system is intended for use with multielectrode silicon probes and is based on a dedicated 64‑channel CMOS chip. It can generate complex sequences of microstimulation pulses and simultaneously record (with low artifacts) neuronal responses at up to 512 electrodes. The system is compatible with most silicon probes used in the brain research and can use up to four probes in parallel, providing bidirectional communication with populations of neurons simultaneously in several brain areas. Each channel of the chip includes a recording amplifier and a stimulation circuit. The amplifier has adjustable gain (110‑550x), low cut‑off frequency (1.4‑7 Hz), and anti‑aliasing filter frequency (1.2‑14 kHz). The input‑referred noise is 6.8 µV. Signals from all the channels are digitized at 40 kHz. The stimulation signal is defined independently for each channel with 40 kHz refresh rate. The stimulation artifacts are reduced by temporally disconnecting the amplifiers from electrodes and optimization of the pulse waveform. METHOD(S): The system has been tested in experiments exploring somatosensory thalamo-cortical network in rodents. 2‑3 weeks before surgery, animals received injections of AAV‑hSyn‑ChR2‑EYFP viral vector. In anesthetized animals, multichannel probes were inserted into the barrel cortex and/or sensory thalamus for recording of LFPs and multi-unit responses to microstimulation delivered to various nodes of thalamo‑cortical network. Electrically evoked activity was compared with responses to natural whisker deflection and optical stimulation. RESULTS: The reported system can generate complex patterns of stimulation pulses and record neuronal signals with very low artifacts at up to 512 electrodes, making it a powerful tool for mapping of the functional connections between brain circuits. FINANCIAL SUPPORT: Supported by Polish National Science Centre grant 2013/08/W/NZ4/00691.
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