The mechanism of coupling of the locust flight oscillator to oscillatory inputs

Summary

• 1. A flying locust responds to a rhythmically flashing light by adopting a wingbeat frequency equal to the flash frequency, if the flash frequency is not too different from the initial wingbeat frequency (Fig. 2). During this response, the wingbeat cycle maintains a particular timing relative to the light cycle (Fig. 1).

• 2. This oscillator coupling occurs because each light flash, by exciting the elevator motor neurons and/or the depressor motor neurons, causes an acceleration of the flight cycle by an amount that depends on the timing of the flash relative to the flight cycle (Figs. 4 and 5). The phase of the flight cycle relative to the flashes changes until it reaches a value at which the acceleration in each cycle is just sufficient to result in a flight system frequency equal to the stimulus frequency. The resulting constant phase relationship is stable only if slight fluctuations in the timing of the flight cycle are self-correcting. As predicted theoretically self-correction occurs in that portion of the cycle in which later stimuli result in smaller accelerations of the flight cycle.

• 3. This mechanism of oscillator coupling has been demonstrated by a similar method of analysis for other biological oscillators (Moore et al., 1963; Enright, 1965). It is shown here how the method of analysis can be extended to certain cases of reciprocally coupled oscillators.

• 4. Some of the data suggest that there may be only one or two layers of neurons in the central nervous network which generates the motor output pattern in flying locusts.