(a)Example high-speed (250 frames/s) video frame showing whiskers of a head-fixed rat during a juxtacellular recording experiment. The pivot point (red dot) and the whisker tracking ROI (green dots) are manually clicked for tracking each video.
(b)Example traces demonstrating the tracking procedure. We rotated adjacent frames around the pivot point shown in (a) to maximize the correlation between the frames within the whisking ROI (‘Pearson’s ρ‘, top trace) and estimated the mean change in angles between adjacent frames (‘ΔAngle’, middle traces). Datapoints with sudden spikes in the correlation between frames due to video artifacts were removed from the traces (example marked by black arrow). To estimate the whisking angle, we linearly interpolated, numerically integrated and band-pass filtered the change in angle between frames (‘Angle’, bottom trace). Grey bar indicates a nose-to-nose touch.
(c)Top: Distribution of βAmpl for all cells is not different from zero (P = 0.204, Wilcoxon signed-rank test, also shown in Fig 3c). Bottom: When we plot only significant cells (assessed by a likelihood ratio test), the pattern is mixed: 10 cells are suppressed (red bars) and 6 cells are activated (blue bars). As a population, they are not different from zero (P = 0.098, Wilcoxon signed-rank test), but we note that the suppressed cells tend to be more strongly modulated that the activated cells: (median |βAmpl|= 0.221/0.128 for suppressed/activated cells, P = 0.00025, Mann-Whitney U-test).
(d)Soma of example juxtacellularly labeled Ctip2-negative cell.
(e)Example recorded data and fitted model from the neuron shown in (d). The top traces show the occurrence of nose-no-nose touches (grey bars), the juxtacellular recording trace with spikes (high-pass filtered at 300 Hz, top trace) and the whisker angle and whisking amplitude (tracked by high-speed videography). Below we show the estimate of the instantaneous firing rate of the best fitted model (green line, smoothed with a Gaussian with σ = 75 ms) plotted on top of an estimate of the observed firing rate (grey area, calculated by convolving the spike train with a Gaussian with σ = 75 ms, clipped at 10 Hz for plotting). This cell was suppressed by nose touch, whisker protraction and by increased whisking amplitude (maximum likelihood estimates: β0 = 0.03, βNose = −0.70, βAngle = −0.30 (°)-1, βAmpl = −0.38 (°)-1)
(f)Fitted betas, when we run the model shown in Fig 3 on stepwise orthogonalized data. In this model, β’Nose measures how the spike rate depends on nose touch, β’Angle measures how the spike rate depends on ‘the variation in whisker angle, which is orthogonal to variations in nose touch’, and β’Ampl measures how the spike rate depends on ‘the variation in whisking amplitude, which is orthogonal to variations in nose touch and variations in whisker angle’. Bars indicate median β, error bars indicate 95% confidence intervals of the median.