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Feasibility of a visual prosthesis for the blind based on intracortical micro stimulation of the visual cortex
Abstract
The feasibility of producing a visual prosthesis for the blind using intracortical microstimulation (ICMS) of the visual cortex was studied in a 42-year-old woman who had been totally blind for 22 years secondary to glaucoma. Thirty-eight microelectrodes were implanted in the right visual cortex, near the occipital pole, for a period of 4 months. Percepts reported as small spots of light, called phosphenes, were produced with 34 of the 38 implanted microelectrodes. Threshold currents for phosphene generation with trains of biphasic pulses were as low as 1.9 microA, and most of the microelectrodes had thresholds below 25 microA. Phosphene brightness could be modified with stimulus amplitude, frequency and pulse duration. Repeated stimulation over a period of minutes produced a gradual decrease in phosphene brightness. Phosphenes did not flicker. The apparent size of phosphenes ranged from a "pin-point' to a "nickel' (20 mm diameter coin) held at arm's length. Phosphene size usually decreased as stimulation current was increased but increased slightly as the train length (TL) was increased. At levels of stimulation near threshold, the phosphenes were often reported to have colours. As the stimulation level was increased, the phosphenes generally became white, greyish or yellowish. Individual phosphenes appeared at different distances from the subject. When two phosphenes were simultaneously generated, the apparent distances of the individual phosphenes sometimes changed to make them appear to be at about the same distance. When three or more phosphenes were simultaneously generated, they became coplanar. Except for rare occasions, phosphenes extinguished rapidly at the termination of the stimulation train. When stimulation TLs were increased beyond 1 s, phosphenes usually disappeared before the end of the train. The duration of phosphene perception could be increased by interrupting a long stimulation train with brief pauses in stimulation. Intracortical microelectrodes spaced 500 microns apart generated separate phosphenes, but microelectrodes spaced 250 microns typically did not. This two-point resolution was about five times closer than has typically been achieved with surface stimulation. With some individual microelectrodes, a second closely spaced phosphene was sometimes produced by increasing the stimulation current. Phosphenes moved with eye movements. When up to six phosphenes were simultaneously elicited, they all moved with the same relative orientation during eye movements. All phosphenes were located in the left hemi-field with the majority above the horizontal meridian. There was a clustering of most of the phosphenes within a relatively small area of visual space. The potentially greater microelectrode density and lower power requirements of ICMS compared with surface stimulation appears encouraging for a visual prosthesis. However, further studies with blind subjects are required to optimize stimulation parameters and test complex image recognition before the feasibility of a visual prosthesis based on ICMS can be established.
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“In early testing with VCPs, stimulation of multiple electrodes produced only percepts of multiple isolated phosphenes which did not combine into coherent forms (Dobelle et al., 1976; Schmidt et al., 1996), a finding we replicated in sighted participants implanted with intracranial electrodes for the pre-surgical evaluation of epilepsy (Bosking et al., 2018a).”
From Dynamic Stimulation of Visual Cortex Produces Form Vision in Sighted and Blind Humans (2020) · cites this paper as Schmidt et al., 1996
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“However, in the study by Schmidt et al., electrodes were implanted individually and many broke early in the experiment; therefore, only very limited testing of pattern recognition could be conducted.”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
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In the citing paper
“Furthermore, phosphene size, stimulation threshold (defined as the minimum current to produce a visible phosphene 50% of the time) and brightness depend on stimulation parameters such as the pulse width, train length, amplitude, and frequency of stimulation (Bak et al., 1990; Schmidt et al., 1996; Winawer and Parvizi, 2016; Bosking et al., 2017; Niketeghad et al., 2020; Fernández et al., 2021).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“Regarding the color of phosphenes, there is still some ambivalence in the reports, including descriptions of phosphene color ranging from black or white to different tones of color (Tehovnik and Slocum, 2007; Tehovnik et al., 2009; Schmidt et al., 1996).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“Our present results support previous findings (5, 10, 38, 39, 41, 42) and show that the border between V1 and V2, which is located near the occipital pole, is a suitable place for a cortical visual prosthesis (37).”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
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“This 2-point resolution is closer than the 500 μ m resolution reported previously with a single electrode pair of gold wire electrodes (10), and about 5 times closer than has been achieved with surface electrodes (2-5, 7).”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
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“and stimulation via electrodes that were spaced close to each other evoked separate phosphenes”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
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“Furthermore, our simulator includes a model of the temporal dynamics, observed by Schmidt et al., 1996, accounting for response-attenuation after prolonged or repeated stimulation, as well as the delayed ‘offset’ of phosphene perception.”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“Figure 4 displays the simulator’s fit on the temporal dynamics found in a previous published study by Schmidt et al., 1996.”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“Note that the effects found by Fernández et al., 2021 (that were modeled by us) are consistent with findings by other studies, which report brighter phosphenes for higher stimulation strengths (Schmidt et al., 1996), and a lower stimulation efficiency (i.e. higher total charge thresholds) for longer pulse trains or higher pulse widths and frequencies (Niketeghad et al., 2020).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“However, in contrast to the findings by Schmidt et al., 1996, our simulator predicts a moderate recovery over the next 1000s.”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“and in cortical prostheses the position of the artificially induced percept will shift along with eye movements (Brindley and Lewin, 1968; Schmidt et al., 1996).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“Notably, increasing the stimulation amplitudes can lead the appearance to shift from colored to yellowish or white (Schmidt et al., 1996).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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In the citing paper
“Dynamic optimization of the stimulation may be necessary to counteract unwanted effects such as response fading due to accommodation after repeated or prolonged stimulation (Schmidt et al., 1996), or delayed phosphene perception after stimulation on- and offset.”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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“The appearance of phosphenes in our simulation (white, round, soft dots of light) are largely in line with previous reports on intracortical stimulation (Schmidt et al., 1996; Bak et al., 1990; Fernández et al., 2021).”
From Towards biologically plausible phosphene simulation for the differentiable optimization of visual cortical prostheses (2024) · cites this paper as Schmidt et al., 1996
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In the citing paper
“The work of Schmidt et al. (10) showed that microstimulation via microelectrodes that penetrated the visual cortex could help to mitigate some of these limitations.”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
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In the citing paper
“Phosphenes could be evoked with stimulation currents in the tens of microamps range”
From Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex (2021) · cites this paper as [10]
In the citing paper
“as has been observed in both the retinal70 and cortical literature34”
From A virtual patient simulation modeling the neural and perceptual effects of human visual cortical stimulation, from pulse trains to percepts (2024) · cites this paper as [34]
In the citing paper
“Previous experimental studies have found it extremely difficult to generate recognizable shapes through stimulation of multiple electrodes34,84.”
From A virtual patient simulation modeling the neural and perceptual effects of human visual cortical stimulation, from pulse trains to percepts (2024) · cites this paper as [34]
In the citing paper
“Third, although our model fits current temporal data reasonably well and includes desensitization due to the refractory period, it is worth noting that various studies have shown longer-scale desensitization with prolonged stimulation in both human34 and macaque89 and this is also observed with retinal prostheses70.”
From A virtual patient simulation modeling the neural and perceptual effects of human visual cortical stimulation, from pulse trains to percepts (2024) · cites this paper as [34]
In the citing paper
“Penetrating electrodes require orders of magnitude less current and produce smaller phosphenes (Schmidt et al., 1996).”
From Writing to the Mind’s Eye of the Blind (2020) · cites this paper as Schmidt et al., 1996
In the citing paper
“This distance reduces the spatial resolution of artificial vision [99], and high currents might be unsafe due to the risk of seizures [88].”
From Advances in visual prostheses: engineering and biological challenges (2022) · cites this paper as [99]
In the citing paper
“Increasing the electrode density increases the risk of having a stimulation cross-talk and current summation when neighbouring electrodes are activated simultaneously.”
From Three-dimensional multilayer concentric bipolar electrodes restrict spatial activation in optic nerve stimulation (2022) · cites this paper as [8]
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Citations
Cites
The sensations produced by electrical stimulation of the visual cortex
Brindley, G. S., & Lewin, W. S. (1968) · The Journal of Physiology · doi:10.1113/jphysiol.1968.sp008519 · Cited by 1,170
Dobelle, W. H., & Mladejovsky, M. G. (1974) · The Journal of Physiology · doi:10.1113/jphysiol.1974.sp010766 · Cited by 468
Dobelle, W. H., Mladejovsky, M. G., & Girvin, J. P. (1974) · Science · doi:10.1126/science.183.4123.440 · Cited by 440
Visual sensations produced by intracortical microstimulation of the human occipital cortex
Bak, M., Girvin, J. P., Hambrecht, F. T., Kufta, C. V., Loeb, G. E., & Schmidt, E. M. (1990) · Medical & Biological Engineering & Computing · doi:10.1007/bf02442682 · Cited by 299
Self-citationParylene as a Chronically Stable, Reproducible Microelectrode Insulator
Loeb, G. E., Bak, M. J., Salcman, M., & Schmidt, E. M. (1977) · IEEE Transactions on Biomedical Engineering · doi:10.1109/tbme.1977.326115 · Cited by 258
Self-citation“Braille” reading by a blind volunteer by visual cortex stimulation
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Activated Ir: An Electrode Suitable for Reversible Charge Injection in Saline Solution
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Latency functions in human vision
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Simple reaction time as a function of stimulus intensity in decibels of light and sound.
Kohfeld, D. L. (1971) · Journal of Experimental Psychology · doi:10.1037/h0030891 · Cited by 119
Flagged first, then by citations
Research works printed but not linked: 3
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Cited by
Sorted by citations
Hartong, D. T., Berson, E. L., & Dryja, T. P. (2006) · The Lancet · doi:10.1016/s0140-6736(06)69740-7 · Cited by 2,924
Neural Stimulation and Recording Electrodes
Cogan, S. F. (2008) · Annual Review of Biomedical Engineering · doi:10.1146/annurev.bioeng.10.061807.160518 · Cited by 2,243
Functional relevance of cross-modal plasticity in blind humans
Cohen, L. G., Celnik, P., Pascual-Leone, A., Corwell, B., Faiz, L., Dambrosia, J., Honda, M., Sadato, N., Gerloff, C., Catala´, M. D., et al. (1997) · Nature · doi:10.1038/38278 · Cited by 911
Will Retinal Implants Restore Vision?
Zrenner, E. (2002) · Science · doi:10.1126/science.1067996 · Cited by 736
Connecting cortex to machines: recent advances in brain interfaces
Donoghue, J. P. (2002) · Nature Neuroscience · doi:10.1038/nn947 · Cited by 720
Metadata
- Authors
- Schmidt, E. M., Bak, M. J., Hambrecht, F. T., Kufta, C. V., O'Rourke, D. K., & Vallabhanath, P.
- Affiliations
- National Institutes of Health (US)
- Howard Hughes Medical Institute (US)
- Corresponding author
- Schmidt, E. M.
- Venue
- Brain
- Publisher
- Oxford University Press (OUP)
- Published
- 1996
- Volume
- 119
- Issue
- 2
- Pages
- 507-522
- ISSN
- 0006-8950 (ISSN-L)
- 1460-2156
- OpenAlex
- W2090285495
- Cited by
- 672
- References
- 17
- Citations by year
- 2026: 13 · 2025: 24 · 2024: 21 · 2023: 20 · 2022: 28 · 2021: 27 · 2020: 31 · 2019: 22 · 2018: 19 · 2017: 13 · 2016: 30 · 2015: 34 · 2014: 20 · 2013: 40 · 2012: 23
- FWCI
- 3.37
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Brain (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neural Engineering
- Life Sciences › Neuroscience › Cognitive Neuroscience › Tactile and Sensory Interactions
- Health Sciences › Medicine › Anesthesiology and Pain Medicine › Pain Management and Treatment
- Keywords
- visual prosthesis, intracortical microstimulation, visual cortex, phosphenes, blindness, glaucoma, two-point resolution, color perception, eye movements, threshold current, feasibility study, neuroprosthetics
- MeSH terms
- Adult, Blindness, Electric Stimulation, Female, Humans, Microelectrodes, Time Factors, Visual Cortex, Visual Perception
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