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Questions and Answers
What was the purpose of creating a localized retinal bleb during the procedure?
What was the purpose of creating a localized retinal bleb during the procedure?
What type of electrodes were used in the stimulation array?
What type of electrodes were used in the stimulation array?
What was the sampling rate for single unit spike activity (SUA)?
What was the sampling rate for single unit spike activity (SUA)?
How were the receptive fields of recorded cortical neurons determined?
How were the receptive fields of recorded cortical neurons determined?
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What was the diameter of the retinotomy made during the procedure?
What was the diameter of the retinotomy made during the procedure?
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What was the frequency range for local field potentials (LFP) sampled?
What was the frequency range for local field potentials (LFP) sampled?
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What type of signals were recorded at a sampling rate of 500 Hz?
What type of signals were recorded at a sampling rate of 500 Hz?
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What material was the flexible foil strip made from?
What material was the flexible foil strip made from?
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What is the spatial resolution achieved with light stimulation during epi-retinal stimulation?
What is the spatial resolution achieved with light stimulation during epi-retinal stimulation?
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What is the range of the composite visually and electrically evoked field responses measured in microvolts?
What is the range of the composite visually and electrically evoked field responses measured in microvolts?
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How long are the response delays noted during the electrical impulses activation of ganglion cells?
How long are the response delays noted during the electrical impulses activation of ganglion cells?
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What type of electrodes provided the high spatial resolution in the study?
What type of electrodes provided the high spatial resolution in the study?
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How many spikes does electrical activation evoke per neuron?
How many spikes does electrical activation evoke per neuron?
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What is the retino-cortical point spread function primarily used for?
What is the retino-cortical point spread function primarily used for?
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How is the width of the spatial distribution of response amplitudes determined?
How is the width of the spatial distribution of response amplitudes determined?
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What effect does a 1 millimeter difference in epiretinal stimulus location have on cortical response?
What effect does a 1 millimeter difference in epiretinal stimulus location have on cortical response?
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What type of response is commonly observed in spatial activation profiles measured with cortical microelectrode recordings?
What type of response is commonly observed in spatial activation profiles measured with cortical microelectrode recordings?
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What range of retinal eccentricities was primarily used for measuring response profiles with cortical microelectrode recordings?
What range of retinal eccentricities was primarily used for measuring response profiles with cortical microelectrode recordings?
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What trend is observed regarding the width of the activation in response components over time?
What trend is observed regarding the width of the activation in response components over time?
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Which spacing of electrode arrays was used in the study for recording?
Which spacing of electrode arrays was used in the study for recording?
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Optical imaging was used to measure the spread of activation in relation to what type of stimulation?
Optical imaging was used to measure the spread of activation in relation to what type of stimulation?
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What magnitude factor was used for normalization in the study?
What magnitude factor was used for normalization in the study?
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What was the estimated full width at half height (FWHH) when measured at a stimulation of 0.2 ms and 24 μA?
What was the estimated full width at half height (FWHH) when measured at a stimulation of 0.2 ms and 24 μA?
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What is the relationship between eccentricity and the activation patch in area 17?
What is the relationship between eccentricity and the activation patch in area 17?
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Which phase duration was associated with an FWHH of 2.7 mm?
Which phase duration was associated with an FWHH of 2.7 mm?
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Which of the following statements correctly reflects the finding related to retinal implants?
Which of the following statements correctly reflects the finding related to retinal implants?
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How was visual field eccentricity addressed in the study?
How was visual field eccentricity addressed in the study?
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What kind of estimates for resolution were obtained in the study?
What kind of estimates for resolution were obtained in the study?
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What stimulation current was associated with an FWHH of 1.7 mm?
What stimulation current was associated with an FWHH of 1.7 mm?
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What is the approximate latency for visual responses compared to electrical stimuli?
What is the approximate latency for visual responses compared to electrical stimuli?
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How long is the duration of visual responses in the optic tract?
How long is the duration of visual responses in the optic tract?
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What type of neurons does cortical action potential activation involve?
What type of neurons does cortical action potential activation involve?
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What is the inter-electrode distance used in the retinal implant mentioned?
What is the inter-electrode distance used in the retinal implant mentioned?
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What is the estimated range of delays for ganglion cell responses to electrical stimuli?
What is the estimated range of delays for ganglion cell responses to electrical stimuli?
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What type of electrode is used to make optic tract recordings?
What type of electrode is used to make optic tract recordings?
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What causes the higher degree of jitter in visual responses compared to electrical stimuli?
What causes the higher degree of jitter in visual responses compared to electrical stimuli?
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What kind of waveform is delivered during the stimulation from the retinal implant?
What kind of waveform is delivered during the stimulation from the retinal implant?
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Study Notes
Retinal Implants
- Study Purpose: The study aimed to determine the spatial resolution achievable with epi-retinal implants, employing a thin-film electrode array inserted into the subretinal space.
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Methods:
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Retinal Stimulation:
- A 2.5-mm retinotomy was created at the temporal portion of a localized bleb.
- A thin-film platinum electrode array (8 electrodes) was inserted through the retinotomy into the subretinal space.
- Electrical stimuli were delivered through the electrodes with varied parameters (amplitude, waveform, frequency).
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Cortical Recordings:
- Cortical neuron activity was recorded using microelectrodes placed in the visual cortex.
- Spatial activation profiles were generated based on the distribution of cortical responses to focal retinal stimuli.
- Optical recordings were also used to assess spatial activation.
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Retinal Stimulation:
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Spatial Resolution:
- The spatial resolution of the retinal implant was estimated from the spread of cortical activation in response to a focal retinal stimulus, referred to as the 'retino-cortical point spread function'.
- Cortical point spread functions were measured using both microelectrode recordings and optical imaging.
- Measured spatial resolution was normalized for different retinal eccentricities using magnification factors from cat visual cortical maps.
- Measured spatial resolutions with microelectrode recordings varied from approximately 1.0 - 2.7mm.
- Normalizing these values to an eccentricity of 2° visual angle resulted in estimated resolutions of 1.4° - 3.8° of visual angle.
- The higher resolution obtained with optical recordings (0.68°) was obtained using cone-shaped microelectrodes.
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Temporal Resolution:
- The temporal precision of primary cortical action potentials was determined by the latency and duration of responses to electrical stimuli.
- Electrical stimulation evoked single impulses in ganglion cells with a repetition jitter of 2–3 ms.
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Comparison to Light Stimulation:
- Responses elicited by electrical stimulation were compared to those evoked by light flashes.
- The latency and duration of electrical responses were much shorter (~2-3 ms) compared to the latency and duration of visually evoked responses (~20-35 ms).
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Implications:
- The study demonstrates that epi-retinal implants can achieve moderate levels of spatial resolution.
- The temporal resolution of the implant is sufficient to evoke single impulses from ganglion cells.
- The results demonstrate the potential of epi-retinal implants to restore vision, particularly for individuals with retinal degenerative diseases.
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Description
This quiz explores the findings of a study on spatial resolution achievable with epi-retinal implants. It covers methods involving retinal stimulation, electrode insertion, and cortical recordings, as well as the implications for visual cortex activation. Test your knowledge of the techniques and results from this innovative research.
