Fig. 5: Irregular otolith afferents show nonlinear responses during running.
a A hypothetical linear neuron’s response to low (top) and high (bottom) amplitude stimulation. In response to high amplitude stimulation, the model predicts negative values resulting in physiological inhibitory cutoff that causes an increase in overall mean firing rate relative to the afferent’s resting discharge. The higher probability of having negative values that result in inhibitory cutoff increases the mean firing rate. b Actual and linear model-predicted probability distributions all afferent classes. The passive-based linear model (Eq. 3) predicts impossible negative firing rates (yellow shaded area; in panels a, b, and c). The probability of zero firing rate (black arrow) was significantly higher for irregular otolith afferents than the other classes of afferents (one-way ANOVA, F(3,45) = 13.45, p = 2.5 × 10−6). c Actual firing rates and linear model predictions across conditions. As shown in panel b, neuron’s nonlinear response (i.e., inhibitory cutoff) resulted in an increase in mean firing rate during high amplitude passive stimulation and running (VAF = 0. 35, and 0.37) for the high amplitude passive pitch and running respectively, while this was not the case for the lower-amplitude stimulation (i.e., walking and walking-matched passive pitch, (VAF = 0.89 and 0.86, respectively). Top right insets: Population-averaged mean firing rates were significantly higher than resting discharges during high amplitude passive motion and running (ANOVA, F(4,52) = 7.8, p = 0.002), which did not differ from each other (p = 0.85). Mean firing rate and resting discharge were comparable for low-amplitude passive pitch and walking were comparable (p = 0.20). For all boxplots, the central mark indicates the median, the middle box indicates the 25th and 75th percentiles and the whiskers extend to the most extreme data points not considered outliers. Source data are provided as a Source Data file.
