Model of change in information rates as a function of transmission jitter and expansive non-linearity.

<p>A surface depicting the percentage change in mutual information between encoding and decoding sites is shown in greyscale for model parametrized by the magnitude of the transmission jitter (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030115#pone-0030115-g001" target="_blank">Fig. 1C</a>) and the time constant of the expansive nonlinearity (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030115#pone-0030115-g002" target="_blank">Fig. 2A</a>). The parameter combinations measured in 8 neurons are shown with grey x's.</p

Measurement of jitter and information rates.

<p><i>A</i>, Comparison of jitter at encoding end (light grey portion of bar) assessed over repeated presentations of stimulus, and transmission jitter (black portion of bar), measured in three different neurons. <i>B</i>, Mutual information rates for the three neurons in <i>A</i>, calculated at the encoding (light grey) and decoding (black) sites. Error bars represent Bayesian 95% confidence interval from CTW calculation.</p

Transmission jitter and fit parameters for all 8 intra-intra and intra-extra experiments.

<p>Transmission jitter and fit parameters for all 8 intra-intra and intra-extra experiments.</p

Change in ISI Distribution and Relation to Stimulus Coding.

<p><i>A</i>, Percentage change in probability of ISI at decoding site relative to encoding site, same data as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030115#pone-0030115-g002" target="_blank">figure 2D</a>. The shaded region indicates ISIs that occur more frequently at the decoding site than at the encoding site. <i>B</i>, The correlation between first and second spikes of ISIs reliably elicited by repeated presentations of identical stimuli (“frozen noise”). <i>C</i>, The linearity of stimuli associated with doublet patterns of spikes with various ISIs, as assessed with log likelihood ratios. Data in <i>B</i> & <i>C</i> are from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030115#pone.0030115-Aldworth2" target="_blank">[28]</a>, reprinted with permission.</p

Conduction failures.

<p><i>A</i>, Simultaneous intracellular recording from encoding (lower trace) and decoding (upper trace) sites in a single 10-2a neuron, showing an instance of an action potential which failed to propagate the length of the axon (red arrows). <i>B</i>, Distribution of spike propagation time as a function of ISI, along with exponential fit (dashed red line), as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030115#pone-0030115-g002" target="_blank">figure 2</a>. Also shown is the length of the preceding ISI for 32 action potentials that failed to propagate (blue circles, arbitrary ordinate position). <i>C</i>, Data are presented as in <i>B</i>, but for a different cell (class 10-3a). Scale bars: <i>A</i>, horizontal, 20 ms; vertical, 5 mV.</p

Our user-assisted digitization process yields results with accuracy comparable to manual digitization.

<p>(A) Each colored bar indicates the mean and standard deviation of the 3D Euclidean distance from the manually digitized point to the same point extracted by our software, for a single walking bout (4096 frames). The colored dots on the scale drawings of the legs have a radius corresponding to approximately the average positional error. (B) Each bar shows the mean and standard deviation of the absolute joint angle error. Joint angle errors were distributed log-normally.</p

Image preprocessing.

<p>Leg outlines for the left leg are drawn as an aid to the reader.</p

Calculation of stride timing.

<p>(A) Enlarged view of a portion of the walking bout shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013617#pone-0013617-g005" target="_blank">Fig. 5</a>. Although it is not obvious, the <i>x</i>-, <i>y</i>-, and <i>z</i>-positions of the TiTa points (shown in black, red, and blue, respectively) are displayed here as points rather than lines to demonstrate the discretization due to the digital video capture. Discontinuities typically occurred when the forward and backward tracking intersected (see Methods). The gray boxes denote the stance phases of each leg, as defined by the leg's <i>z</i>-coordinate. The dashed, green boxes show how the stance phase calculation changes when the foot's anterior and posterior extreme positions (AEP and PEP, respectively) are used to determine stride timing.</p

Experimental setup.

<p>(A) The recording configuration. A cockroach was glued to a flexible tether and walked in place on a plate of oiled glass. One camera was slightly to the front of the animal and the other viewed its ventral surface through a mirror. (B) Ventral view of a cockroach, <i>Blaberus discoidalis</i>, with the body colored black for contrast. The colored dots on the legs indicate the points which were marked and then tracked by our software. The black arrows at right indicate the coordinate system used in this analysis, with the <i>z</i>-axis extending into the page (shaded cube added to indicate depth). The <i>x</i> and <i>y</i> vectors shown would be approximately 1 cm in length. (C) Details of digitized points and definitions of joint angles. (D) Reduction of the trochanter-femur (TrF) joint results in lowering the foot toward the substrate. (E) The thorax-coxa (ThC) joint has three rotational degrees of freedom in the front leg; in the middle and hind legs, only the first two degrees of freedom are actuated.</p

Parameters used to calculate stride timing.

<p>(A) Fourier power spectra of the legs' <i>x</i>-positions, for the same walking bout shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013617#pone-0013617-g005" target="_blank">Fig. 5</a>. Green: raw amplitude; black: filtered amplitude. The peak frequency in the black curves is the initial estimate of the stepping rate by each leg. (B) Histograms of the <i>z</i>-positions of the legs' tibia-tarsus (TiTa) joints during the same walking bout. Each histogram is fit with a 2-component Gaussian mixture model (colored traces), with the mean and variance of the lower-valued cluster (pink) used to help determine whether or not the foot was touching the substrate. (C,E,G) Power spectra for other trials, each with a different average step rate (note the different frequencies of the peak power). Panels E and G show the middle legs only. (D,F,H) <i>Z</i>-histograms for the same bouts.</p