Firing-rate tuning by running speed in the entorhinal cortex of rats differs across time scales. Time scale-dependent speed scores allow clustering of neurons recorded in the rat entorhinal cortex into different speed-cell categories. A, Clustergram showing hierarchical clustering of 665 single units recorded in MEC of 11 rats. Each row depicts color-coded speed scores calculated for each time scale ranging, exponentially increasing, from 1 to 2 s up to 256–512 s (see Materials and Methods). Distinct clusters of clearly speed-modulated neurons can be identified. B, Mean ± SEM of time scale-dependent speed scores of clusters identified in A. C–E, Data on one speed-modulated example cell in Cluster B. C, Time scale-dependent speed tuning. Black dots show binned data (time-scale filtered firing rate vs time-scale filtered running speed); red lines show the least-square linear fits to binned data, r = Pearson correlation coefficient. D, The overall speed tuning curve of the example cell. Black dots and gray shading show mean values and 95% confidence intervals of speed-binned firing-rate data; blue and red lines show the best MLE linear (blue) and saturating exponential (red) fit functions obtained by temporal binning of firing rate, shadings indicate 95% confidence intervals. E, Slopes of observed time scale-dependent speed tuning curves for the example cell (orange curve) compared with mean ± SEM of slopes derived from 100 artificially created linearly tuned Poisson-distributed spike trains (blue line, SEM within line). F, Mean ± SEM of mean-normalized speed tuning curve slopes across all cells (orange, positively speed-modulated cells of Clusters A and B; blue, artificially created Poisson-distributed spike trains, one Poisson train per cell, n = 182). Observed spike trains differ significantly from artificial ones, F(11,4344) = 26.00, p = 0.0000, two-way ANOVA interaction effect. G, Left, Distribution of optimal bandwidths for firing-rate estimation. Right, Population average (mean ± SEM) of bandwidth-dependent log-likelihoods of firing-rate estimates. H, Population average (mean ± SEM) of bandwidth-dependent speed-score distributions.
