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.

中文翻译：

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多电极刺激唤起光幻视的一致空间模式并改善盲人的光幻视映射

背景

视觉皮层假体 (VCP) 有可能恢复获得性失明患者的视觉功能。VCP 的成功实施需要能够可靠地映射由每个植入电极的刺激产生的磷化氢的位置。

客观的

评估不同方法对 phosphene 映射的功效，并提出对映射策略的简单改进。

方法

我们刺激了植入五名盲人和十五名视力正常患者的视觉皮层的电极。我们测试了两种固定策略，单手固定，受试者将单个食指放在触觉固定点和双手固定，受试者将右手食指覆盖在触觉点的左侧。此外，我们比较了在每次试验中刺激单个电极的绝对映射，以及在每次试验中包含刺激三到五个光幻视的序列的相对映射。量化了相对映射序列中存在的试验间变异性。

结果

盲人受试者的磷化氢映射不如有视力的受试者精确（2DRMS，16 ± 2.9° vs. 1.9 ± 0.93°；t (18) = 18，p = <0.001）。在盲人受试者中，双手固定导致比单手固定更一致的光幻视定位（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)。多点相对映射与绝对映射具有相似的基线精度（BS1：4.7 ± 2.6° vs. 3.9 ± 2.0°；BS2：4.1 ± 2.0° vs.3.2 ± 1.1°），但在去除试验间平移变异性后显着改善。尽管多点映射方法确实揭示了早期视觉皮层中预期的更多功能组织，但受试者倾向于人为地调整光幻视之间的间距。我们试图通过将标准对数映射拟合到相对多点序列来解决这个问题。

结论

相对映射方法与双手固定相结合，可以最精确地估计 phosphene 组织。这些技术，结合使用视觉皮层的标准对数模型，可以提供改进 VCP 实施的实用方法。