Fig. 2.

Optical flows associated with nine different leech motoneurons. A–I show the optical flow computed on a 30 × 20 grid for the skin deformations caused by intracellular stimulation of motoneurons L, 3, 5, 107, 8, 108, 110, CV, and 109, respectively. The data were obtained from seven different preparations. Each motoneuron was stimulated with a depolarizing step of current causing a spike discharge between 30 and 40 Hz and lasting from 1 to 6 sec. Optical flows were obtained as described in Zoccolan et al. (2001)and Materials and Methods. A drawing of the segment annuli is shown ingray in each panel, and annulus width is between 0.5 and 0.8 mm. Scale bars, 2 mm. The top boundary of the preparation is the dorsal midline of the body; thebottom boundary is between the lateral line and the ventral midline. Anterior is to the left. The central annulus of the innervated segment is, starting fromleft: the sixth for A, G,H, and I; the fifth for B,D, and F; the fourth forC; and the eighth for E. The region of optical flow framed by the solid box was used to compute the linear approximations shown in Figure 3. To make the direction of the movement more clear, the fields shown in E,F, G, and I are drawn with a magnification respectively 1.5, 2, 1.5, and 2× larger.