Fig. 6: Taking into account response nonlinearity reveals that irregular otolith afferents similarly encode locomotion and passive motion.
a During running, the example irregular otolith afferent’s response as a function of acceleration was well fit by a sigmoid (black sigmoid). The same nonlinearity accurately described this afferent’s responses during high amplitude passive head motion (inset, R2 = 0.83). b The population-averaged response as a function of acceleration was comparable during high amplitude passive head motion (gray dots) and running (red sigmoid). Shaded area represents ± 1 STD of the population average nonlinear function during running. c Schematic of the linear-nonlinear cascade model. In this model the output firing rate is calculated by first linearly filtering the input stimulus and then passing the resulting linear prediction through a static nonlinear function. d Top panel: The bias estimated using the linear-nonlinear cascade model was comparable between conditions (walking: slope = 1.01, p = 0.002, CI = 0.45, intercept = 5.9 sp/s, p = 0.6; running: slope = 1.06, p = 3.2 × 10−4, CI = 0.35, intercept = 6.9sp/s, p = 0.07). Inset: population-averaged bias values for each condition (ANOVA, F(2,26) = 1.7, p = 0.25). Bottom panel: The modulation of irregular otolith afferents is comparable across conditions when using a nonlinear model that accounts for the afferent’s responses to large-amplitude head accelerations (walking: slope = 1.06, p = 3.0 × 10−6, CI = 0.25; running: slope = 1.09, p = 2.8 × 10−7, CI = 0.20; inset: ANOVA, F(2,26) = 2.1, p = 0.14). e Schematic showing that the responses of semicircular canal afferent and regular otolith afferent responses remain in their linear coding range during all conditions (striped green area), but irregular otolith afferent responses extend into a nonlinear coding range during running. Shaded areas represent ± 1 STD of the population average firing rate. 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.
