Preparing for escape: An examination of the role of the DCMD neuron in locust escape jumps

Many animals begin to escape by moving away from a threat the instant it is detected. However, the escape jumps of locusts take several hundred milliseconds to produce and the locust must therefore be prepared for escape before the jumping movement can be triggered. In this study we investigate a locust's preparations to escape a looming stimulus and concurrent spiking activity in its pair of uniquely identifiable looming-detector neurons (the descending contralateral movement detectors; DCMDs). We find that hindleg flexion in preparation for a jump occurs at the same time as high frequency DCMD spikes. However, spikes in a DCMD are not necessary for triggering hindleg flexion, since this hindleg flexion still occurs when the connective containing a DCMD axon is severed or in response to stimuli that cause no high frequency DCMD spikes. Such severing of the connective containing a DCMD axon does, however, increase the variability in flexion timing. We therefore propose that the DCMD contributes to hindleg flexion in preparation for an escape jump, but that its activity affects only flexion timing and is not necessary for the occurrence of hindleg flexion.