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E. L. Nylen, S. F. Stasheff; Using Information Theory to Quantify Functional Capacity in Retinal Disease. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1875.
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© ARVO (1962-2015); The Authors (2016-present)
Information theoretical methods have provided a useful means of quantifying characteristics of communication in neural systems. We use such methods to describe how inherited retinal disease influences the message the brain receives from the eye.
Extracellular action potentials were recorded simultaneously from 30-90 retinal ganglion cells in the in vitro retina of 14 day old wild type (wt) and rd1 mice, using a multi-electrode array. Spontaneous activity was monitored and full field light flashes were presented over a range of illuminance values. The mutual information between stimuli and responses was calculated for each recorded cell, and background spontaneous activity was quantified in terms of spike count, rate, and Shannon entropy.
The entropy of all spike trains in rd1 cells (N=99) was 15.6 bits, and in wt cells (N=79) 16.5 bits. This measure of entropy estimates the overall cellular signaling capacity for a large group of cells. The input-output fidelity of these cells can be characterized by isolating each cell's unique responses to stimuli, described as the mutual information between stimulus and response. The wt cells showed a mean mutual information of 5.4 bits per cell, while the rd1 displayed a significantly less mean mutual information of 2.1 bits per cell (Mann-Whitney U Test, p <0.001).
In our study of the rd1 mouse, an animal model of retinitis pigmentosa, we quantitatively show that an increase in spontaneous firing activity of retinal ganglion cells may affect these cells' capacity to send distinguishable messages. At postnatal day 14 though, the spontaneous activity observed in rd1 does not completely mask the retina's response to light stimulation. Our findings suggest that, despite aggressive photoreceptor degeneration and an increase in noise, retinal ganglion cells' signal capacity may be sufficient for administration of successful visual restoration therapies in early stages of disease.
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