FIG. 1.

The custom-built impact device (a). A, XY plate; B, stage for mouse; C, XYZ translator; D, linear actuator (provides electromagnetic force); E, flexure (restricts motion so impactor tip moves only at the desired z-direction); F, digital micrometer (used to set the impact distance); G, laser displacement transducer (measures the impact distance, i.e., displacement of the impactor tip); H, impactor tip (13 mm diameter); I, mouse holder. (b) Measured impact displacements during phantom impacts (n = 10) at various impact depths: 0.3 mm (□), 0.6 mm (△), and 0.9 mm (◯). Data are expressed as mean ± standard deviation. Since the impact is conducted from the dorsal to ventral direction, a negative sign represents upward motion. The solid, bold line represents the command pulse (voltage, not related to the y-axis units). The zero point is indicated with an arrow. These displacement profiles during phantom impacts show high correspondence with desired trajectories, at impact depths from 0.3 to 0.9 mm, for both upward and downward motion.