Figure 2. Merkel and unidentified afferents respond to both active touch and self-motion.

(A) Zoomed region of a high-speed video frame showing a whisker in contact with the pole. Whisker-pole contact force (F⇀) can be decomposed into the force components acting along the axis of the whisker ( $\stackrel{\rightharpoonup }{F_{ax}}$) and lateral to the face ( $\stackrel{\rightharpoonup }{F_{\mathit{lat}}}$). Magnitudes of these forces and of the bending moment ( $\stackrel{\rightharpoonup }{M_0}$) induced by F⇀ were estimated for each video frame. (B) Example time series for a Merkel afferent. One second of electrophysiological recording (top trace) is shown with mechanical variables estimated from the high-speed video, including whisker angular position (θ), phase of θ within the whisk cycle (ϕ), whisker angular velocity (ω), whisker angular acceleration (α), whisker angular jerk (ζ), and magnitude of contact-induced moment (M₀), axial force (F_ax) and lateral force (F_lat). Periods of whisker-pole contact are indicated by lavender shading. (C) Mean spike rates of neurons during periods when the mouse was not whisking (light gray symbols), during whisking in free air (dark gray), and during whisker-pole contact (lavender). Error bars indicate 95% bootstrap confidence intervals of the means. Data points for each neuron are connected by black lines. Neurons are sorted along the horizontal axis by rapidly adapting (lower red bar) or slowly adapting (lower gray bar) properties, positive Merkel afferent identification (lower blue bar), and sensitivity to touch (T, upper dashed bars) or to both whisking and touch (WT, upper solid bars). A subset of afferents especially sensitive to whisking in air (referred to as “WT*” in the text) are indicated with asterisks. See also Video S1.