Changes in locomotor activity parameters with variations in cycle time in larval lamprey.

In larval lamprey, locomotor activity recorded from whole animals and in vitro brain/spinal cord preparations was analyzed to determine how two parameters of locomotor activity, burst proportion (BP; relative duration of motor burst activity) and intersegmental phase lag (phi; normalized delay of burst activity along one side of the body), vary with changes in cycle time (T). In individual animals, the slopes of BP and phi versus T were compared using linear regression analysis, followed by statistical analysis of the slopes to determine whether the parameters changed significantly with variations in cycle time. For locomotor muscle activity in whole animals, the BP values increased significantly with decreases in T (i.e. negative slopes), while the slopes for phi values versus T were not significantly different from zero. For locomotor activity in preparations in vitro, the mean slopes for BP values versus T, although negative, were not significantly different from zero, and phase lags were also relatively constant with changes in cycle time. Increases in BP with decreases in cycle time and increases in swimming speed can be expected to generate proportionately more force per cycle, presumably to compensate for the increase in viscous resistance of moving the body more rapidly through water. By contrast, constant intersegmental phase lags will ensure that the relative timing of locomotor burst activity is constant and that an approximately single S-wave along the body is retained during different swimming speeds.