Journal: The Journal of Neuroscience

Article Title: Categorical Signaling of the Strongest Stimulus by an Inhibitory Midbrain Nucleus

doi: 10.1523/JNEUROSCI.0042-20.2020

Figure Lengend Snippet: Imc signals stimulus competition with greater precision, and earlier than OTid. A, Distributions of biases of competitor response profiles of OTid neurons (blue; n = 36 neurons with correlated competitor response profiles; median = −0.83; p = 0.62; sign test against 0 and Imc neurons (red; data reproduced from Fig. 4B; n = 66; median = −0.52). No significant difference between Imc and OTid medians (p = 1.0, sign test after Holm–Bonferroni correction for multiple comparisons). B, Proportions of switch-like (S), gradual (G), and uncorrelated (U) competitor response profiles measured in Imc (stacked bar on left; n = 78 neurons at which competitor response profiles where measured) and OTid (middle bar; n= 53 neurons at which competitor response profiles were measured). Previously published OTid proportions (n = 169 neurons at which competitor response profiles were measured; data adapted from Mysore et al., 2011) are also shown for completeness (right bar; unfilled). * (n.s.): χ2 statistic = 5.21, p = 0.02 (p = 1.0), χ2 test between Imc and OTid proportions measured here followed by Holm–Bonferroni correction for multiple comparisons. C, Comparison of d-prime (Materials and Methods) computed from pooled competitor response profile responses measured in OTid (blue) versus Imc (red). *p = 0.01, permutation test (Materials and Methods). Inset, Schematic of pooled competitor response profile responses across neurons illustrating d-prime computation across the selection boundary (vertical gray line). D, Pooled instantaneous firing rates (IFRs) of OTid neurons with gradual competitor response profiles in response to S1 alone (gray) or paired S1 and S2 (green), binned into five relative strength bins (columns). E, Millisecond-by-millisecond running ANOVA to determine time to suppression (vertical dashed line): the first instant at which responses to paired S1 and S2 diverge significantly from responses to S1 alone (Materials and Methods). OTid responses never diverge significantly for the first relative strength bin (S2-S1 = −7 °/s; left-most panel). F, G, Same as E and F, but for OTid neurons with switch-like competitor response profiles (magenta data); OTid responses never diverge significantly for the first relative strength bin (S2-S1 = −7 °/s; left-most column). H, Population summary: Scatter plot of time to suppression for OTid neurons versus Imc neurons for the different relative strength bins (i.e., scatter plot of green numbers in D versus magenta numbers in F). Dots, (Imc, OTid) time to suppression pairs for the different relative strength bins; magenta data, switch-like competitor response profiles; green data, gradual competitor response profiles; progressively larger dots indicate increasing relative strength (S2-S1). For plotting purposes, time to suppression values corresponding to cases in which the responses to paired S1 and S2 never diverged from those to S1 alone, are coded as 450 ms. Dashed line: line of equality. Inset, Boxplot of differences between OTid and Imc time to suppression values; *p = 0.02, sign test against 0.

Article Snippet: To characterize the responses to the paired presentation of S1 and S2 (i.e., competitor response profiles), we calculated the correlation (Pearson, corrcoef command in MATLAB) as a function of the strength of S2.

Techniques: Comparison, Selection

Journal: The Journal of Neuroscience

Article Title: Categorical Signaling of the Strongest Stimulus by an Inhibitory Midbrain Nucleus

doi: 10.1523/JNEUROSCI.0042-20.2020

Figure Lengend Snippet: Switch-like and gradual response suppression of Imc neurons by a competing stimulus. A, Schematic of experimental setup and stimulus protocol for measuring competitor strength-dependent response profiles (CRPs). Quadrilateral, Tangent monitor; dashed oval, RF of recorded Imc neuron; black dot; S1 visual looming stimulus; magenta dots, S2 visual looming stimulus. Sizes of dots denote loom speeds. B, C, Responses of an example Imc neuron with switch-like competitor response profile (data in magenta). B, Rasters of spike responses to S1 alone (left; loom speed = 3.6°/s) and to the paired stimuli (right) showing an abrupt increase in suppression with increasing S2 strength. Shaded box along the y-axis represents stimulus duration (250 ms), and dashed lines denote the time window (100–250 ms) during which response firing rates were calculated. C, Response firing rates corresponding to rasters in B. Open circle and horizontal dotted line response firing rate to S1 alone (mean ± SEM); filled circles with graded grey shading, response firing rates to paired presentation of S1 and S2 (i.e., CRP; mean ± SEM; darker colors indicating higher firing rates). Correlation coefficient of responses versus S2 strength = −0.74 (p = 0.04, Pearson correlation test). Solid line, Best fitting sigmoid to the competitor response profile (r2 = 0.95); vertical dashed lines, transition range of this competitor response profile (0.17°/s; Materials and Methods); black arrowhead, strength of S1 (3.6°/s). D, E, Responses of an example Imc neuron with gradual competitor response profile (data in green). Conventions are as in B and C. Loom speed of S1 = 5.6°/s, correlation coefficient of responses versus S2 strength = −0.94, p = 0.0002, Pearson correlation test; r2 = 0.99 for the best fitting sigmoid; transition range = 5.75°/s. F, Histogram of transition ranges of competitor response profiles that exhibited a negative correlation with the strength of S2 (n = 66 neurons/78 total). Vertical line: “cutoff” transition range of 4°/s (see “Materials and Methods”). The median strength of S1 was 7°/s with 95% CI of 6.3°/s, 7.7°/s; median distance of S2 from S1 = 43° with 95% CI of 40° 46°. Inset, RF locations (in double-pole coordinates) of Imc neurons at which competitor response profiles were recorded; colors correspond to whether the neurons had switch-like (magenta) or gradual (green) competitor response profiles.

Article Snippet: To characterize the responses to the paired presentation of S1 and S2 (i.e., competitor response profiles), we calculated the correlation (Pearson, corrcoef command in MATLAB) as a function of the strength of S2.

Techniques:

Journal: The Journal of Neuroscience

Article Title: Categorical Signaling of the Strongest Stimulus by an Inhibitory Midbrain Nucleus

doi: 10.1523/JNEUROSCI.0042-20.2020

Figure Lengend Snippet: Time course of response suppression for Imc neurons with switch-like versus gradual competitor response profiles (CRPs). A–D, Analysis of response time courses of Imc neurons with gradual competitor response profiles; columns, responses binned by the relative strength of S1 and S2 (S2-S1). A, B, Instantaneous firing rates (IFRs) of neurons to S1 alone (A) or to S1 and S2 presented together (B), computed by smoothing PSTHs (1 ms time bins) with a Gaussian kernel (SD = 12 ms; Materials and Methods). For each neuron, instantaneous firing rates are normalized by the peak firing rate of that neuron to S1 alone. Neurons in A are sorted by the half-peak firing rate; neurons in B are in the same order as in A. C, Pooled average firing rates to S1 alone (gray) or to S1 and S2 (green) of all neurons within each bin. Translucent bands indicate SEM. D, Time course of p values obtained by performing ANOVA between the responses to S1 versus to S1 and S2 at each millisecond. Vertical dashed arrows (and colored text), time to suppression (defined as the first instant at which responses to paired S1 and S2 diverge significantly from responses to S1 alone; Materials and Methods); horizontal dashed lines, p value thresholds used in determining time to suppression (bottom line, p = 0.05; top line, p = 0.01. E–H, Same as A–D, but for Imc neurons with switch-like competitor response profiles. I, Comparison of time to suppression for neurons with switch-like (magenta) versus gradual competitor response profiles (green) J, Plot of average amount of response suppression (±SEM) for switch-like versus gradual neurons for the two relative strength bins on either side of the selection boundary. Text reports the effect size (η2).

Article Snippet: To characterize the responses to the paired presentation of S1 and S2 (i.e., competitor response profiles), we calculated the correlation (Pearson, corrcoef command in MATLAB) as a function of the strength of S2.

Techniques: Comparison, Selection

Journal: The Journal of Neuroscience

Article Title: Categorical Signaling of the Strongest Stimulus by an Inhibitory Midbrain Nucleus

doi: 10.1523/JNEUROSCI.0042-20.2020

Figure Lengend Snippet: Signatures of stimulus competition at simultaneously recorded, aligned Imc and OTid sites. A, Schematic of experimental setup for simultaneous, paired recordings in Imc and OTid. S1 and S2, Stimulus protocol for measuring competitor response profiles; colored icons to the left, recording electrodes, positioned in OTid (blue) and Imc (red); dashed ovals, RFs of recorded site. B, Raster plots of responses for example paired, aligned Imc (left panels) and OTid (right panels) sites; distance between RF centers = 8° (Materials and Methods). Top panels, Responses to S1 alone. Bottom panels, Responses to S1 and S2 presented together. Strength of S1 = 9.6°/s. All other conventions similar to Figure 1B. C, Firing rate responses corresponding to rasters in B. Conventions are as in Figure 1C. Competitor response profile correlation values: Imc = −0.81, (p = 0.009); OTid = −0.99, p < 0.05 (p = 0.0000004). Competitor response profile transition ranges: Imc = 2.8°/s (switch-like competitor response profile); OTid = 15.3°/s (gradual competitor response profile). Competitor response profile transition values: Imc = 4.1°/s; OTid = 6.2°/s. D, Scatter plot of competitor response profile biases measured at paired Imc and OTid sites (n = 17 pairs; average distance between RF centers = 6.3 ° ± 0.95 °). Dashed gray line, line of equality; solid purple line, best fit line to data; Pearson's ρ = 0.6, p = 0.01. E, Scatter plot of transition ranges of competitor response profiles measured at paired Imc and OTid sites. Dashed gray lines, cutoff value of transition ranges (4 °/s) for switch-like versus gradual competitor response profiles. F, Plot of difference in transition ranges of competitor response profiles (OTid − Imc; top) or biases of competitor response profile (OTid − Imc; bottom) for paired Imc-OTid sites as a function of distance between Imc and OTid RFs. Pearson's ρ = 0.03, p = 0.9 (competitor response profile transition ranges); ρ = 0.07, p = 0.8 (competitor response profile biases). G, I, Response time courses for OTid (G; blue) and Imc sites (I; red) recorded simultaneously; shown are the pooled averages across OTid sites, and separately, across Imc sites (conventions are as in Fig. 2). H, J, Results from the millisecond-by-millisecond AVOVA are also shown for OTid (H; blue) and Imc sites (J; red), respectively. Columns, Relative strength bins; IFR, instantaneous firing rate. Horizontal dashed lines, p value cutoffs (0.05, bottom line; 0.01, top line); vertical dashed arrows (and colored text), time to suppression; Materials and Methods). K, Scatter plot of time to suppression measured at aligned Imc versus OTid sites recorded simultaneously. Each dot, time to suppression pair for a different relative strength bin; data correspond to the colored numbers in G and I. Dashed line: line of equality. Pearson's ρ = 0.99, p = 0.0007.

Article Snippet: To characterize the responses to the paired presentation of S1 and S2 (i.e., competitor response profiles), we calculated the correlation (Pearson, corrcoef command in MATLAB) as a function of the strength of S2.

Techniques: