Descending Interneurones of the Locust Reporting Deviation from Flight Course: What Is Their Role in Steering?

Some descending intemeurones (DNs) in insects encode deviation from flight course. Intracellular recording reveals their inputs (from eyes, wind hairs, proprioceptive information from the neck and in some cases ocelli). Intracellular stimulation during flight reveals their motor effects. All components of steering (modification of wing stroke, ruddering with the hind legs, ruddering with the abdomen and head rotation) can be initiated by single DNs. Steering in flight involves the concerted action of at least 10 pairs of DNs synapsing with motor neurones and premotor intemeurones. The whole system forms an autopilot, well suited for corrective steering. It is modulated principally by head movements, which have both optical and proprioceptive effects: compensatory head movements increase the accuracy of correctional steering by reducing overshoot, and disable the autopilot during turns evoked by directional pulsed ultrasound for purposes of bat-evasion. DNs responding specifically to visual flow fields are also known, but appear to be related to control of velocity rather than to steering.