Fig. 2. (A) Simultaneous recordings from EMG signals and wing position during tethered flight (see Fig. 1C,D). Note the slow time course and variable amplitude of EMG events. The first burst of neural events had a frequency (44 Hz; this is presumably an artifact of tethered flight) that resulted in relatively little wing motion. The second burst is at a lower frequency, which resulted in a higher wingbeat amplitude and an average vertical force that was 1.87 times body weight (measured simultaneously from a strain gauge; that trace is not shown here). (B) Examples of recordings made by Simmons (Simmons, 1977b), which have been reproduced here to match the relative amplitude and time scale of the EMG traces shown in A. Simmons’ data are (i) from intracellular electrodes in a flight muscle motor neuron during low-frequency wing flapping, (ii) from intracellular electrodes in a motor neuron caused to fire by peripheral electrical stimulation at the muscle and (iii) from an extracellular suction electrode attached to a small group of muscle fibers during tethered flight. Both intra- and extracellular recordings show variability in the time course and amplitude of spikes. The time base shown in A applies also to B.