Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects
Background: Visual cortical prostheses (VCPs) have the potential to restore visual function to patients with acquired blindness. Successful implementation of VCPs requires the ability to reliably map the location of the phosphene produced by stimulation of each implanted electrode. Objective: To eva...
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doaj-3d757164fb724f2084e65dd81f72f9ec2021-09-23T04:37:24ZengElsevierBrain Stimulation1935-861X2021-09-0114513561372Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjectsDenise Oswalt0William Bosking1Ping Sun2Sameer A. Sheth3Soroush Niketeghad4Michelle Armenta Salas5Uday Patel6Robert Greenberg7Jessy Dorn8Nader Pouratian9Michael Beauchamp10Daniel Yoshor11Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA; Corresponding author. Perelman School of Medicine, Department of Neurosurgery, 3700 Hamilton Walk, Richards 6A, Philadelphia, PA, 19104, United States.Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USADepartment of Neurosurgery, Baylor College of Medicine, Houston, TX, USADepartment of Neurosurgery, Baylor College of Medicine, Houston, TX, USADepartment of Neurosurgery, University of California Los Angeles, Los Angeles, CA, USADepartment of Neurosurgery, University of California Los Angeles, Los Angeles, CA, USASecond Sight Medical Products, Sylmar, CA, USASecond Sight Medical Products, Sylmar, CA, USASecond Sight Medical Products, Sylmar, CA, USADepartment of Neurological Surgery, University of Texas Southwestern, Dallas, TX, USADepartment of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USADepartment of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USABackground: Visual cortical prostheses (VCPs) have the potential to restore visual function to patients with acquired blindness. Successful implementation of VCPs requires the ability to reliably map the location of the phosphene produced by stimulation of each implanted electrode. Objective: To evaluate the efficacy of different approaches to phosphene mapping and propose simple improvements to mapping strategy. Methods: We stimulated electrodes implanted in the visual cortex of five blind and fifteen sighted patients. We tested two fixation strategies, unimanual fixation, where subjects placed a single index finger on a tactile fixation point and bimanual fixation, where subjects overlaid their right index finger over their left on the tactile point. In addition, we compared absolute mapping in which a single electrode was stimulated on each trial, and relative mapping with sequences containing stimulation of three to five phosphenes on each trial. Trial-to-trial variability present in relative mapping sequences was quantified. Results: Phosphene mapping was less precise in blind subjects than in sighted subjects (2DRMS, 16 ± 2.9° vs. 1.9 ± 0.93°; t (18) = 18, p = <0.001). Within blind subjects, bimanual fixation resulted in more consistent phosphene localization than unimanual fixation (BS1: 4.0 ± 2.6° vs. 19 ± 4.7°, t (79) = 24, p < 0.001; BS2 4.1 ± 2.0° vs. 12 ± 2.7°, t (65) = 19, p < 0.001). Multi-point relative mapping had similar baseline precision to absolute mapping (BS1: 4.7 ± 2.6° vs. 3.9 ± 2.0°; BS2: 4.1 ± 2.0° vs. 3.2 ± 1.1°) but improved significantly when trial-to-trial translational variability was removed. Although multi-point mapping methods did reveal more of the functional organization expected in early visual cortex, subjects tended to artificially regularize the spacing between phosphenes. We attempt to address this issue by fitting a standard logarithmic map to relative multi-point sequences. Conclusions: Relative mapping methods, combined with bimanual fixation, resulted in the most precise estimates of phosphene organization. These techniques, combined with use of a standard logarithmic model of visual cortex, may provide a practical way to improve the implementation of a VCP.http://www.sciencedirect.com/science/article/pii/S1935861X21002266Visual cortical prosthesisElectrical stimulationCortexPhospheneMapping |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Denise Oswalt William Bosking Ping Sun Sameer A. Sheth Soroush Niketeghad Michelle Armenta Salas Uday Patel Robert Greenberg Jessy Dorn Nader Pouratian Michael Beauchamp Daniel Yoshor |
spellingShingle |
Denise Oswalt William Bosking Ping Sun Sameer A. Sheth Soroush Niketeghad Michelle Armenta Salas Uday Patel Robert Greenberg Jessy Dorn Nader Pouratian Michael Beauchamp Daniel Yoshor Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects Brain Stimulation Visual cortical prosthesis Electrical stimulation Cortex Phosphene Mapping |
author_facet |
Denise Oswalt William Bosking Ping Sun Sameer A. Sheth Soroush Niketeghad Michelle Armenta Salas Uday Patel Robert Greenberg Jessy Dorn Nader Pouratian Michael Beauchamp Daniel Yoshor |
author_sort |
Denise Oswalt |
title |
Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
title_short |
Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
title_full |
Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
title_fullStr |
Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
title_full_unstemmed |
Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
title_sort |
multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects |
publisher |
Elsevier |
series |
Brain Stimulation |
issn |
1935-861X |
publishDate |
2021-09-01 |
description |
Background: Visual cortical prostheses (VCPs) have the potential to restore visual function to patients with acquired blindness. Successful implementation of VCPs requires the ability to reliably map the location of the phosphene produced by stimulation of each implanted electrode. Objective: To evaluate the efficacy of different approaches to phosphene mapping and propose simple improvements to mapping strategy. Methods: We stimulated electrodes implanted in the visual cortex of five blind and fifteen sighted patients. We tested two fixation strategies, unimanual fixation, where subjects placed a single index finger on a tactile fixation point and bimanual fixation, where subjects overlaid their right index finger over their left on the tactile point. In addition, we compared absolute mapping in which a single electrode was stimulated on each trial, and relative mapping with sequences containing stimulation of three to five phosphenes on each trial. Trial-to-trial variability present in relative mapping sequences was quantified. Results: Phosphene mapping was less precise in blind subjects than in sighted subjects (2DRMS, 16 ± 2.9° vs. 1.9 ± 0.93°; t (18) = 18, p = <0.001). Within blind subjects, bimanual fixation resulted in more consistent phosphene localization than unimanual fixation (BS1: 4.0 ± 2.6° vs. 19 ± 4.7°, t (79) = 24, p < 0.001; BS2 4.1 ± 2.0° vs. 12 ± 2.7°, t (65) = 19, p < 0.001). Multi-point relative mapping had similar baseline precision to absolute mapping (BS1: 4.7 ± 2.6° vs. 3.9 ± 2.0°; BS2: 4.1 ± 2.0° vs. 3.2 ± 1.1°) but improved significantly when trial-to-trial translational variability was removed. Although multi-point mapping methods did reveal more of the functional organization expected in early visual cortex, subjects tended to artificially regularize the spacing between phosphenes. We attempt to address this issue by fitting a standard logarithmic map to relative multi-point sequences. Conclusions: Relative mapping methods, combined with bimanual fixation, resulted in the most precise estimates of phosphene organization. These techniques, combined with use of a standard logarithmic model of visual cortex, may provide a practical way to improve the implementation of a VCP. |
topic |
Visual cortical prosthesis Electrical stimulation Cortex Phosphene Mapping |
url |
http://www.sciencedirect.com/science/article/pii/S1935861X21002266 |
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