Fig. 1. (A) Positioning of electrodes for recording the activity in RS pathways. One array (electrodes 1 and 2) was implanted at the level of the third gill, and the other array (electrodes 3–6) 20–30 mm more caudally. (B) Arrangement for recording vestibular responses in RS neurons. The lamprey was positioned in the tube and rotated around its longitudinal axis (, roll tilt angle). (C) A representative example of vestibular responses in RS pathways and individual RS axons in the animal compensated after the left unilateral labyrinthectomy (UL). Two sequential full turns (clockwise and counterclockwise) were performed in 45° steps. Shaded rectangles indicate the normal (horizontal) orientation of the animal. Positions of the animal in successive steps (in relation to the direction of gravity force) are shown. The left half of the lamprey body is shaded. Vestibular responses were measured separately for each of the three intervals of a step (inset); the activity in interval 1 (during rotation) will be considered as a dynamic response, the activity in intervals 2 and 3, as early and late static responses, respectively. Traces E1 and E2 show the mass activity in RS pathways recorded by the left and right electrodes of the rostral array, respectively (electrodes 1 and 2 in A). Seven neurons were separated from the mass activity using the spike-sorting program. The neurons L1–L3 had their axons located on the left, ipsilateral to the UL side of the spinal cord (i-UL group). The neurons R1-R4 had their axons located on the right, contralateral to the UL side (co-UL group).