Korean J Physiol Pharmacol.  2009 Jun;13(3):221-227. 10.4196/kjpp.2009.13.3.221.

Accurate Representation of Light-intensity Information by the Neural Activities of Independently Firing Retinal Ganglion Cells

• Ryu SB
• Ye JH
• Kim CH
• Goo YS
• Kim KH

• KMID: 2071675
• DOI: http://doi.org/10.4196/kjpp.2009.13.3.221

Abstract

For successful restoration of visual function by a visual neural prosthesis such as retinal implant, electrical stimulation should evoke neural responses so that the information on visual input is properly represented. A stimulation strategy, which means a method for generating stimulation waveforms based on visual input, should be developed for this purpose. We proposed to use the decoding of visual input from retinal ganglion cell (RGC) responses for the evaluation of stimulus encoding strategy. This is based on the assumption that reliable encoding of visual information in RGC responses is required to enable successful visual perception. The main purpose of this study was to determine the influence of inter-dependence among stimulated RGCs activities on decoding accuracy. Light intensity variations were decoded from multiunit RGC spike trains using an optimal linear filter. More accurate decoding was possible when different types of RGCs were used together as input. Decoding accuracy was enhanced with independently firing RGCs compared to synchronously firing RGCs. This implies that stimulation of independently-firing RGCs and RGCs of different types may be beneficial for visual function restoration by retinal prosthesis.

Keyword

Retinal prosthesis; Retinal ganglion cell; Multielectrode arrray (MEA); Optimal linear filter; Spike train decoding; Functional connectivity

MeSH Terms

Electric Stimulation
Fires
Light
Neural Prostheses
Retinal Ganglion Cells
Retinaldehyde
Visual Perception
Visual Prosthesis
Retinaldehyde

Figure

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  Fig. 1. Temporal patterns of light stimulus intensity variation. Dotted: original stimulus, Solid: reconstructed stimulus by spike train decoding. (A) ON-OFF stimulus (ON: 2 s, OFF: 5 s, decoding from 4 ON RGCs), (B) Gaussian random stimulus (decoding from 5 ON RGCs). The light intensity (y axis) is represented with respect to the minimum and maximum intensity (‘0’ and ‘1’ denote the minimum and the maximum intensity levels, respectively). Frame rate was 1 Hz.

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  Fig. 2. Examples of cross-correlograms for two synchronously-firing (A), and independently-firing (B) RGCs.

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  Fig. 3. Structure of an optimal linear decoding filter for multiple RGC spike trains.

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  Fig. 4. Variation of the decoding accuracy as a function of the number of filter taps. (A) ON cells (1~4 cells), (B) OFF cells (1~4 cells), (C) 2 ON cells and 2 OFF cells used together for the decoding. Each data point was obtained from 3 repeated trials of decoding from 100 s data. Error bars denote standard error.

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  Fig. 5. (A) Variation of the decoding accuracy as a function of frame rate, for Gaussian random stimuli obtained from 21 repeated trials (3 trials×7 cell groups), (B) Comparison of the decoding results of synchronously- firing and independently-firing RGCs, for Gaussian random stimuli (8 stimuli×3 trials×7 cell groups).

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