Ght in the Locust

after deviatio extensions of the contralate position (Get 1970; Arbas, (Camhi, 1970 (Zarnack and Möhl, 1977; Taylor, 1981b; Thüring, 1986; Schmidt and Zarnack, 1987) and compensatory head rolling (Camhi, 1970; Hensler, 1988; Robert and Rowell, 1992) are also involved in flight steering. The motor system of hindleg ruddering has only been grossly described, whereas the motor system which produces modulation in the wing stroke is relatively well understood. The latter is brought about by phase shifts in the discharge time of flight motoneurones within the wingbeat cycle. These are caused by convergent summation of exteroceptive sensory information about deviation from course, mainly from windsensitive head hairs (Weis-Fogh, 1949; Goodman, 1959), from the compound eyes and from the ocelli (Taylor, 1981a,b; Thüring, 1986), with information from the neuronal oscillator flight ed by ex nsory in g cereb ak con 80; Row l as str interneurones (TINs). These TINs are also postsynaptic to the neuronal oscillator for flight (Reichert and Rowell, 1985; Rowell and Reichert, 1991). This has two important consequences. First, TINs and flight motoneurones will only fire action potentials in response to sensory information if they also receive input from the neuronal oscillator, i.e. only during flight. Second, because the oscillator signal is rhythmically modulated, summation will cause action potentials only during the depolarising phases of the cycle, i.e. the phase-independent sensory information becomes coupled to the flight motor, preventing disruption of the rhythmicity of the behaviour (Reichert and Rowell, 1985; Reichert, 1989). Recordings during fictive flight from neck or abdomen motoneurones in dissected animals, as well as from associated The Journal of Expe Printed in Great Brit