Fig. 5. Left/right coupling mediated through the L3–L6 segments. A, Rhythmic activity (left; induced by 6 μm 5-HT and 6 μm NMDA) before the lesion in a Th12–L6 preparation, shown together with alinear plot of 25 consecutive phase values (middle) and a circular plot of 25 random cycles covering the whole episode of rhythmicity (right). B1, B2, Rhythmic activity (B1, B2, left), linear (B1, B2, middle) and circular (B2, right) phase plots in the same preparation after a hemisection of the Th12–L2 segments (indicated in the schematic, B1, right). During the first part of the recording, sudden changes in period, not affecting contralateral bursting, appeared on both sides. As a result, two bursts could occur on one side that were not separated by a contralateral burst onset (B1, left andmiddle). Later, the period became more constant, but phase drift now occurred (B2, left andmiddle). These features indicating looser coupling were not observed before the lesion. Coupling was still significant, although the concentration of phases around the mean was reduced (compare A, right andB2, right). C, Rhythmic activity induced by lower drug concentrations (5.5 μm5-HT, 5.5 μm NMDA) after the lesion in the same preparation as in A, B1, andB2. The concentration of phase values around the mean again increased (C, middle andright), and the coupling was not significantly lower than during bursting in the higher concentration before the lesion (compare A, right and C,right).