001, Z test) These results also suggest that a DCMD firing rate

001, Z test). These results also suggest that a DCMD firing rate threshold plays a trial-by-trial role in determining the onset of cocontraction but that other neurons may contribute

as well. To quantify the steepness of the threshold, we plotted the extensor firing rate as a function of the DCMD firing rate and computed the DCMD firing rate change resulting in the extensor sweeping from 5% to 25% of its peak rate (Figure S4F). On average the corresponding relative DCMD firing rate change amounted to ∼5% and was thus approximately four times steeper than Romidepsin manufacturer that of the extensor (20%). So far, the results suggest that the DCMD strongly contributes to the execution of various phases of looming-evoked escape behaviors. We next asked:

Is the DCMD activity necessary for their generation? To address this question, we sectioned one of the two nerve cords (nL = 6) and presented looming stimuli to the eye ipsi- or contralateral to the intact nerve cord. We compared the timing and probability of take-off before and after this procedure. We found that, irrespective of the stimulated eye, these locusts still took off and that the timing of take-off remained as positively correlated with l/|v| as in control experiments (ρ = 0.9, p < 10−9). Moreover, the NVP-BGJ398 supplier take-off time was not significantly different when the stimulus was presented to the eye ipsi- or contralateral to the remaining nerve cord ( Figure 7A) and was significantly delayed only for l/|v| = 40 ms ( Figure 7B; a similar result was obtained at l/|v| = 30 ms, data not shown). The variability in the take-off time was however increased, as reported previously for the time of the initial flexion in tethered locusts ( Santer et al., 2008). Additionally, the probability of take-off was reduced on average by 51% (SD: 24%) for stimulation of

the eye ipsilateral to the intact cord and 64% (SD: 27%) for stimulation of the contralateral eye. These reductions were not significantly different from each other (pKWT = 0.42). Since locusts with a nerve cord sectioned contralateral to the stimulated eye jump at the same time as control animals, there must exist at least one looming sensitive neuron in the ipsilateral nerve cord whose activity is functionally equivalent to that of the DCMD. This neuron may be the very descending ipsilateral movement detector neuron (DIMD), which responds to the motion of small targets similarly to the DCMD ( Rowell, 1971 and Burrows and Rowell, 1973). The DIMD has not been identified anatomically but is known to generate spikes that in some animals are in one-to-one correspondence with those of the DCMD. Furthermore, based on electrophysiological recordings, it is thought to make a monosynaptic connection with the FETi, whose EPSPs summate with those induced by the DCMD. The DIMD is therefore a strong candidate for a mirror symmetric neuron with an equivalent role in generating escape behaviors.

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