Activity of an identified wind interneurone in a flying locust

Abstract

LOCUST flight has been intensively studied by behavioural physiologists. The basic flight rhythm seems to be generated within the thoracic ganglia¹, although its timing is modified from wing beat to wing beat by phasic input from the wing sense organs². In this way, the basic motor score is possibly tuned to operate at the resonant, most energetically efficient frequency of the individual insect, and adjusted to accomodate changes in wing movements caused by variations of the external air current. Sensory influences on the flight motor neurones do not only originate at the wings. Weis-Fogh has demonstrated that stimulation of the wind-sensitive head hairs causes tonic excitation of these motor neurones³. Here, we have recorded in the locust during flight, the activity of two of the interneurones that convey wind information from the head hair afferents to the thoracic ganglia. These interneurones, the tritocerebral commissural giants (TCG)^4,5, receive their afferent wind hair input in the brain and make excitatory connections with flight motor neurones in the thoracic ganglia⁶. We show that these cells are rhythmically active during flight, synchronous with the wing beat, as a result of periodic stimulation of the head hairs. It is therefore possible that the wind-hair sensory system has a phasic influence on the flight motor as well as the already clearly established tonic influence.