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Spikes

The mean spike number averaged over all 400 flies showed a significant (p<0.001) decrease in a linear fashion from 65 spikes in the first to 29 spikes in the last 2 min period (Fig. 12). Between-group variation was not significant. Heisenberg and Wolf (1979) have reported a spike frequency of 0.5-1 spike/s which is confirmed by the present study.

Figure 12
Fig. 12: Mean spike numbers for all four groups (N=100 flies each) during unreinforced flight. Open symbols indicate standard groups, filled symbols indicate classical groups. Lines are drawn for better illustration only.

The average spike during unreinforced flight (periods 1, 2, 5, 8 and 9) had an amplitude of 1.19 ((0.01 S.E.M) ·10-11 Nm, which seems rather well in accordance with the data in Heisenberg and Wolf (1979), Heisenberg and Wolf (1984) and Mayer et al. (1988). Fig. 13 shows only little variation in spike amplitude during the experiment albeit the pre-test values of the flies in the standard experiment are significantly higher than those of the control group (p<0.001 at t1). However, the difference is only moderate compared to the absolute values (12%) and equalized during the course of the experiment.

Figure 13
Fig. 13: Mean spike amplitudes in arbitrary units (1 unit = 3.9·10-14 Nm) for all four groups (N=100 flies each) in the unreinforced periods. Note the high spike amplitude of the flies in the standard experiment at t1 (periods 1 and 2). Open symbols indicate standard groups, filled symbols indicate classical groups. Lines are drawn for better illustration only.

The mean spike duration of all 400 flies was 0.48s ((0.004s S.E.M) and in three groups it did not show much variation during the course of the experiment (p=0.526, Fig. 14). Only the classically conditioned flies showed a prolonged spike duration after training (periods 5, 8 and 9), compared to the control group (p<0.02). This is considered to be attributable to the heat, as discussed below (3.6). The measured mean duration of a spike (0.48s) is well in accordance with data given in Heisenberg and Wolf (1979). Such rather long spike duration, however, is only achieved in stationary flight without proprioreceptive feedback from angular acceleration or reafferent stimuli from air currents abruptly terminating the burst of torque (after 120-160ms) in free flight.

Figure 14
Fig. 14: Mean spike durations during periods 1, 2, 5, 8 and 9 for all four groups (N=100 flies each). The long duration in the classical conditioning group is obvious (see text). Lines are drawn for better illustration only.

The mean angular displacement caused by detected spikes was 21.7° ((0.25° S.E.M) averaged over all 400 flies. This value was rather constant throughout the experiment and showed little between-group variation (Fig. 15). This is a little less than the "roughly 30°" reported in Heisenberg and Wolf (1979), however, it is not clear whether the number given in this reference was meant to describe wildtype strain Berlin or Canton S or Drosophila in general.

Figure 15
Fig. 15: Mean angular displacement covered by the spikes of all four groups (N=100 each). Lines are drawn for better illustration only.

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