Characteristics of the cells exhibiting significant STRF compared with those exhibiting no significant STRF using vocalizations and Dynamic Moving Ripples (DMRs).

<p>Unpaired t-tests were used to determine if the parameters differed between these 2 types of cells.</p

Comparison between the STRF parameters derived from the STRF_voc and the STRF_dmr.

<p>A. Scattergram showing the values of the BF derived from the STRF_voc (abscissa) against the values of the BF derived from the STRF_dmr (ordinates). For half of the cases, the values are similar (dots around the diagonal line) whereas for the other half, the values derived from the STRF_dmr were higher than those derived from the STRF_voc. B. Scattergram showing the bandwidth values derived from the STRF_voc (abscissa) against the bandwidth value derived from the STRF_dmr (ordinates). In many cases, the values were lower with STRF_voc indicating a larger bandwidth of excitatory responses when tested with vocalizations. C. Scattergram showing the latency values derived from the STRF_voc (abscissa) against the bandwidth value derived from the STRF_dmr (ordinates). The latencies of the excitatory responses were often similar but, in some cases, they were lower with DMRs than with vocalizations. STRF units and scale are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050539#pone-0050539-g002" target="_blank">Figure 2</a>.</p

Statistics of the two sets of stimuli: Guinea-pig vocalizations and Dynamic Moving Ripples (DMRs).

<p>A. and B. Spectrograms of guinea-pig vocalizations. The chutter call is made of sound bursts in the medium frequency range (A). Whistle calls are high-pitched sounds rising in frequency whereas purr calls contain repetitions of low frequency sound bursts (B). C. Spectrogram of a DMR. All spectrograms are in logarithmic frequency scale. D. Average spectrum of our stimuli. The average spectrum of all DMRs is represented by the black line; the average spectrum of the vocalizations by the dashed dark grey line. The light grey line represents the spectrum of each vocalization file used. The vocalizations were selected to obtain a flat spectrum matching closely that of the DMRs. E. Modulation spectrum of the vocalizations and DMRs. As shown, both stimuli spanned the same range of temporal and spectral modulations. F. Distribution of sound intensity in 20 ms time bins calculated for both DMRs (filled-black line) and vocalizations (dashed dark grey line). Light grey lines show the distribution of sound intensity for each vocalization. The difference between the two distributions reflects the existence of large amplitude fluctuations through time in guinea-pig calls.</p

Inter-trial variability.

<p>A. Comparison between the inter-trial variability and the predictive power. The inter-trial variability computed with the Correlation Coefficient between PSTH (CC_psth-psth) is compared for each cell to the predictive power for the vocalizations (A1) and the DMR (A2). In most of the cases (black stars in A1 and A2), CC_psth-psth is significantly higher (paired t-test, p<.05) than CC_voc (A1) or CC_dmr (A2). In very few cases (black dots), CC_psth-psth is not significantly different than CC_voc or CC_dmr. B–C. Examples of four neurons showing either a low (B) or a high (C) spike timing reliability. For each plot, the neuron’s STRF (top) is shown, together with the raster plot (middle) of 20 responses to the stimulus for which the spectrogram (frequency vs. time) is represented on the bottom. Values inserted along the raster plots are the values of the trial-by-trial spike timing reliability as computed with the Rcorr. B1 and B2 show responses with a low spike-timing reliability, whereas C1 and C2 show responses with a high spike-timing reliability. Insets in each STRF show the AP waveforms. STRF units and scale are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050539#pone-0050539-g002" target="_blank">Figure 2</a>.</p

Across stimuli STRF predictions.

<p>Top: Scattergram showing the CC values when STRF_dmr are used to predict responses to DMR (CC_dmr, ordinates) against CC values when STRF_voc is used to predict responses to DMR (_CCvoc2dmr, abscissa). Bottom: Scattergram showing the CC values when STRF_voc are used to predict responses to vocalizations (CC_voc, ordinates) against CC values when STRF_dmr is used to predict responses to vocalizations (CC_dmr2voc, abscissa). In both cases, the large majority of values are higher when the same stimulus set is used for computing the STRF and for predicting the response (dots are mainly above the diagonal line).</p

Individual examples for four neurons exhibiting either similar (A. and B.) or different (C. and D.) STRFs derived from responses to vocalizations (top row) and responses to dynamic moving ripples (DMR, bottom row).

<p>For each STRF, the color code represents “excitation” in red and “inhibition” in blue, units are in spikes/(sec²*dB). In A. and B., the neurons display relatively similar STRFs with vocalizations and DMRs: The best frequency (BF) was similar with vocalizations and DMRs (6.5 kHz in A and B) and the excitation area was circumscribed to the same frequency range, despite some differences in the overall shape. Thus, the similarity index (SI, indicated between the two rows) was relatively high (0.45 and 0.38). In C. and D. the neurons display quite different STRFs estimated from responses to vocalizations and DMRs; in particular, the BF, the shape and the frequency range of the excitatory area differed. Therefore, the values of the SI are low (0.17 and 0.00). Insets in each STRF show the AP waveform during presentation of the stimuli.</p

Predictions between measured responses and predicted responses based on the STRF_voc (top, A and C) and on the STRF_dmr (bottom, B and D) quantified by the Correlation Coefficients (CC).

<p>A–B. Individual examples showing the actual measured responses for a neuron presenting good predictions (JL21HE; left panel) and a neuron presenting poor predictions (JL14GE, middle panel). The top row shows the responses to vocalizations corresponding to spectrograms displayed on the top with the measured responses in blue and the predicted responses in red. The bottom row shows the responses to DMR corresponding to spectrograms displayed on the top (blue curve, measured responses; red curve, predicted responses). C1–C2. Distributions of the CC values for the STRF_voc (A) and for the STRF_dmr (B). The mean value of 0.29 obtained for the STRF_voc is significantly higher than the mean value obtained for the STRF_dmr (0.19). The CC values presented here are for STRF_voc tested on vocalization responses and for STRF_dmr tested on DMR responses.</p

Comparison between STRFs obtained from single action potentials (STRF_AP) and from bursts (STRF_Burst).

<p>A., B. and C. show examples of cells exhibiting relatively similar STRF_AP and STRF_Burst (SI>0.5). In the three cases, the main excitatory zone is in the same frequency range for STRF_AP and STRF_Burst; differences are mainly observed in small excitatory and inhibitory areas. Note that inhibition zones are more prominent in STRF_Burst than in STRF_AP. D. Example of differences between STRF_AP and STRF_Burst (SI<0.5). The maximal excitatory zone is different for the Burst response than for the single APs response. E. Distribution of SI between STRF_AP and STRF_Bursts (mean SI = 0.39±0.22). The distribution shows a continuous range of SI values indicating that bursts of spikes can produce, on average, a STRF relatively similar to the STRF produced by single APs. STRF units and scale are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050539#pone-0050539-g002" target="_blank">Figure 2</a>.</p

Individual mean growth functions for the eCAP amplitude in chronic animals.

<p>Each graph shows the mean (±SEM) eCAP amplitude as charge increases in the six chronic animals (C1-C6). Each curve was plotted with all the recording sessions (excluding the 1^st week) in a given animal. Blue curves represent eCAP amplitudes measured when charges were increased by an increase in pulse amplitude; red curves represent eCAP amplitude measured when charges were increased by an increase in pulse duration. The evolution of these two curves markedly differed from one animal to the next. Note that for some animals (C1, C2), the shape of these two curves roughly follow those shown in the group data (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0201771#pone.0201771.g002" target="_blank">Fig 2B</a>). In contrast, for other animals (e.g., C5, C6) the two curves clearly differ from the group data (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0201771#pone.0201771.g002" target="_blank">Fig 2B</a>).</p

Relationship the PA/PD ratio at the eCAP and cortical level.

<p>For each acute animal, the ratio between the eCAP maximum amplitude triggered by the PA and PD strategy was plotted against the ratio between the strength of all cortical responses obtained with the PA and the PD strategy. At the level of the eCAP, the last 3 points of the growth function shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0201771#pone.0201771.g005" target="_blank">Fig 5</a> were considered; at the cortical level, the responses of all the electrodes responding at the 3 last charge levels were pooled together. There was a significant correlation between the values of the PA/PD eCAP and the values of the PA/PD cortex (r = 0.895; p<0.001) indicating that the strategy producing the largest eCAP amplitude, also produced the largest cortical responses.</p