The tritocerebral commissure giant (TCG) wind-sensitive interneurone in the locust

Summary

• 1. The TCG interneurone of the locust integrates information from the wind-sensitive head hairs and the antennae. The cell is rhythmically active in tethered flight and is sensitive to a yaw imposed on the animal in a laminar stream of air — the left TCG is more sensitive to a yaw to the left and vice versa (Figs. 1, 5).

• 2. Successively waxing over the different windhair fields (fields 1...5) and immobilising the antennae reveals that all these sense organs contribute to the sensitivity of the neurone to the angle of yaw (Figs. 2, 3). There is no mutual inhibition between the right and left TCG (Fig. 4).

• 3. The cell shows a phasic-tonic reaction when either the resting or the flying animal is subjected to a stepwise yaw. However, the tonic component is stronger when the animal is flying (Fig. 7).

• 4. During flight the TCG fires rhythmically in bursts synchronised with depressor muscle potentials, i.e., at about the time when the wing is in its top position. Yaw angle is coded by the number of spikes per burst and their timing within the wing-beat cycle. An increase of the TCG activity is correlated with an earlier beginning of the burst (Figs. 8, 9). There is no change in the interspike interval within the TCG burst during a yaw stimulus: the 1st and 2nd interspike intervals remain at an average of about 4 ms (Fig. 9).

• 5. In straight flight, electric stimulation applied to the right TCG neurone (thus mimicking a yaw to the right) evokes antagonistic time shifts in downstroke muscles, equivalent to those observed in response to an actual right yaw being imposed on the animal (Figs. 10, 11). The results suggest that the TCG is an important pathway in mediating yaw-correcting behaviour.

• 6. A small resetting of the flight rhythm is produced when the TCG is electrically stimulated during flight (Fig. 13).