Electrical receptive field properties.

<p>A) Proportions of cells with up to three excitatory components. B) Proportions of cells with up to three suppressive components. C). The temporal windows over which suppressive and excitatory ERFs affected cell responses, thus indicating duration of stimulus integration time. Excitatory ERFs tended to occur within a short latency from the response (blue circles). Suppressive ERFs tended to extend over a long duration, which was variable from cell to cell (orange circles). The squares represent the means for all cells. D) RGC preference to cathodic-first or anodic-first stimulation. Squares represent means and lines indicate ±1 standard deviation. Stars denote significant differences (<i>p</i> < 0.05).</p

Dendritic and electrical receptive fields.

<p>a-b) Sample cells depicting the stimulating array (large black discs) and the patch-clamp recording electrode (denoted by a *). Overlaid on the images are the morphological reconstructions of the cells. The sample cell in (a) is also shown in (c) 16. The sample cell in (b) is also shown in (c) 20. Note that the stimulating electrodes appear large, but the exposed area is only 400 μm. Also visible are the lycra threads used to keep the retina affixed and the stimulating electrode tracks. c) The electrical receptive fields shown together with the dendritic receptive field estimates. The electrodes with stars above them show the approximate location of the optic disc for each preparation.</p

Electrical receptive fields of retinal ganglion cells: Influence of presynaptic neurons - Fig 7

<p>Number of excitatory (A) and suppressive (B) components before and after application of synaptic transmission blockers (CdCl₂).</p

Model validation for a sample cell.

<p>A) The predicted response was compared to the average responses (black dots with SEM bars). Each point represents the mean response to 200 stimuli. B) The variance of each point in (A) was compared to the prediction. Both values were normalized to the maximum prediction (~3 spikes). For a Poisson-like process, the values should be equal (indicated by the dashed line). C) The contours of fixed response expectation (dotted black) were computed using the predicted model parameters (Eq (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005997#pcbi.1005997.e101" target="_blank">6</a>)). These contours were compared to the contours generated from the experimental data (solid black) when projected onto the principal excitatory component and the second excitatory component (left), third excitatory component (middle), or a suppressive component (right). The contours denote the expectations of 1 and 2 spikes.</p

Model comparison with non-Gaussian stimuli.

<p>A) Distribution of electrode amplitudes for Gaussian and non-Gaussian image stimuli. The amplitudes in both cases have been divided by the variance of the Gaussian stimuli (i.e., the Gaussian distribution has unit variance). B) The model prediction for a sample cell is shown for Gaussian stimuli (round) and images (square). C) Coefficient of determination (R²) of the model prediction when validated with noise and with images for eleven cells. The x denotes the mean R² for noise (0.86) and images (0.70). Dashed line represents line of equality. D) A comparison of the coefficients of determination for the general quadratic model (GQM), non-linear input model (NIM), a two-dimensional spike-triggered covariance analysis (STC₂), and a one-dimension model (STC₁). Squares denote the mean and lines denote ±1 standard deviation.</p

<i>In vitro</i> stimulation and recording.

<p>The retina was placed on a multi-electrode array (large black circles) and held in place with a perfusion chamber and lycra threads. A) Two extracellular electrodes were used to obtain recordings from the retinal surface. B) A hole was made in the inner limiting membrane to expose the RGCs. Once exposed, an intracellular glass electrode was used to obtain whole cell recordings of RGCs.</p

The effect of synaptic blockers.

<p>A) A raster plot of spike times for a sample cell prior to application of CdCl₂. B) The eigenvalues produced from STC analysis showing three significant eigenvalues (arrows). C) A raster plot of spike times for the same cell as in (A) after application of CdCl₂. While spontaneous spikes can be seen at times, long-latency activity was mostly abolished. D) The eigenvalues produced from STC analysis showing only one significant eigenvalue. E) The ERFs corresponding to before (left) and after (right) application of CdCl₂. F) A comparison of the electrode amplitudes making up the ERFs of , before and after application of CdCl₂.</p

Sample light and electrical responses.

<p>A) An example ON cell responds with increased activity when light is switched on (onset marked with a triangle). The inset shows the overlaid spikes from a trial (gray) and the averaged response (black). B) The ON cell from A was stimulated with a spot of light centred at the electrode location. Light was switched on then off five times, each time for 10 s. The process was repeated seven times for this cell. Shown is the average spike rate during <i>light off</i> and <i>light on</i> periods (top) and the instantaneous spike rate 1 s prior to and after a change in illumination (bottom). Error bars represent standard deviations; * denotes a significant change in <i>light on</i> periods compared to <i>light off</i> (one-way ANOVA, p < 0.05). C) A sample cell showing the spikes in response to 10 electrical pulses over a 1 s period. Stimulation artefacts were removed online by blanking. Inset shows an expanded view of the stimulus artefact after removal. The remaining waveform reveals spikes detectable within 5 ms from stimulus onset. D) Intracellular recording showing action potentials (black trace) in response to electrical stimulation. Timing of electrical pulses is shown by traces at the top (grey). The expanded view shows how spikes can be detected with very low latency after artefact blanking.</p

White noise stimulation amplitudes.

<p>(a) The increase in spike probability with increasing amplitude of the standard deviation of the white noise for two cells. To avoid over stimulation of recorded cells, white noise stimulation with a standard deviation (σ) was initially applied to each cell. The value of σ corresponding to half the maximal spike probability was used as the standard deviation of white noise stimulation for the experiment. Cell 1 reached a maximum value close to 1. The value of σ corresponding to a 0.5 spike probability was 85 μA. Cell 2 reached a maximal value close to 0.6. The value of σ corresponding to a spike probability of 0.3 was 145 μA. Error bars refer to the standard deviation from the mean. (b) The σ values from (a) were used to generate Gaussian distributions from which stimulation amplitudes on each electrode were sampled. Stimulus amplitudes were limited to ±300 μA, hence the distribution is truncated at these values.</p

Population data.

<p>(a) Threshold recovered from the nonlinear function for positive and negative regions for all cells; no significant differences were found between cell types (p > 0.3). (b) The correlation coefficients of the positive and negative electrical receptive fields ( and ). (c) Radius of electrical influence for 21 cells. Shown is the approximate range of electrical influence for anodic-first stimulation (<i>D</i>⁺) and the dendritic field size for each cell. Cells were only significantly influenced by one (open circle), two (closed circle) or three (square) electrodes in the ERF. (d) Histogram showing the value of <i>G</i> (Eq (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004849#pcbi.1004849.e057" target="_blank">10</a>)) for all cells. 20 of the 25 cells recovered a that was 4 or more times larger than .</p