Figure 1.
Schematic representation of the heat maze apparatus.
Note: The floor of the maze consists of a 5×5 array of Peltier elements, below an opaque sheet of paper, that provides the maze with both negative reinforcement and one safe zone (analogous to the platform of the Morris water maze). Ground landmarks (in non-spatial experiments) or wall patterns (in spatial experiments) provide visual cues. The paths of flies were video-tracked using a USB camera and computer software.
Figure 2.
Experimental apparatus and setups.
Note: (A) Heat reinforcement of the maze. (B) Proximal and distal cues setup of experiment 1. (C) Training procedures of control, test and random flies during experiment 2.
Figure 3.
Performance of flies in locating the safe zone using either proximal cues (i.e., non-spatial task; n = 20) or distal visual cues (i.e., spatial task; n = 20).
Note: Flies presented either the non-spatial and spatial tasks improved their performance in locating the safe zone: the latency before a 20 s contact with the safe zone decreased (proximal: F(1,52) = 11.57, p = 0.001; distal: F(1,224) = 16.32, p<0.001), the time spent in the safe zone increased (proximal: F(1,52) = 16.03, p<0.001; distal: F(1,223) = 10.67, p = 0.001), the mean distance to the safe zone decreased (proximal: F(1,52) = 10.23, p = 0.002; distal: F(1,224) = 13.81, p<0.001) and the distance moved outside the safe zone declined (proximal: F(1,52) = 9.33, p = 0.003; distal: F(1,224) = 8.37, p = 0.004) with trials. The comparison between non-spatial and spatial tasks revealed no significant differences (latency before a 20 s contact: F(1,294) = 0.17, p = 0.68; time in safe zone: F(1,293) = 0.01, p = 0.93; mean distance to the safe zone: F(1,294) = 3.18, p = 0.08), except for a larger distance travelled in the spatial task (F(1,294) = 12.96, p<0.001). Male and female flies were pooled. Error bars indicate standard errors.
Figure 4.
Spatial learning in Drosophila flies.
Note: (A) Latency before 20 s contact, time spent in the safe zone and mean distance to the safe zone showed a significant improvement after six 5 minute trials for both control and random groups of flies. Most measured variables showed this trend: the latency before a 20 s contact diminished linearly (linear within subject contrast: F(1,77) = 19.6, p<0.001), the time spent in the safe zone increased (F(1,79) = 20.6, p<0.001), the mean distance to the safe zone declined (F(1,78) = 24.84, p<0.001). In contrast, the distance moved outside the safe zone did not improve (F(1,78) = 3.8, p = 0.06). Wall pattern reversal significantly altered the ability for test flies to locate the safe zone as shown by their latency to reach the safe zone and their overall distance moved (Dunnett's test for multiple comparison: latency fo first 20 s contact: p = 0.004; distance moved: p = 0.002). Test flies were also undistinguishable from naïve flies for three variables (latency before 20 s contact: t(115) = 0.01, p = 0.99; time in safe zone: t(112) = −0.75, p = 0.45; distance moved outside safe zone: t(115) = −1.67, p = 0.10). Control flies were significantly different from naïve flies for all variables (latency before 20 s contact: t(117) = 2.17, p = 0.03; time in safe zone: t(112) = −2.36, p = 0.02; distance to safe zone: t(117) = 3.51, p = 0.001; distance moved outside safe zone: t(117) = 2.02, p = 0.05). Performance from the random group of flies improved throughout trials (linear within subject contrast: latency before 20 s contact: F(1,38) = 11.6, p = 0.002; time in safe zone: F(1,39) = 9.89, p = 0.003; distance to safe zone: F(1,39) = 10.3, p<0.001; distance moved outside safe zone: F(1,39) = 0.3, p = 0.92). Statistical significance is indicated with asterisks for linear within subject contrasts and Dunnett's tests (***: p<0.001; **: p<0.01; NS: non-significant). N = 120 female flies. (B) Presence probability plots of control, test and random groups during each 5 minute trials of experiment 2. All groups developed a positional preference for the safe zone through trials. During the seventh trial, test flies displayed a reduced positional preference for the safe zone in comparison to control flies. The white dashed square represents the expected position of the safe zone relative to distal visual cues. (C) Presence probability plots of control and test flies during each minute of the seventh trial of experiment 2. Wall pattern reversal resulted in a both delayed and less intense positional preference for the safe zone in test flies when compared to control flies.
Figure 5.
Parameter-based classification of search strategies.
Note: (A) Detailed presentation of the algorithm-based classification of search strategies, including their key parameters and cut-off values. Exclusion of different strategies was performed in a particular order (from the most to the least spatial) because of the less specific nature of certain strategies. [stdU] represents radius length. (B) Control flies significantly decreased their use of thigmotaxis and random search in favor of non-spatial and spatial search strategies. In contrast, random flies failed to show a significant trend toward using a particular strategy, despite abandoning thigmotaxis. Our algorithm successfully classified more than 96% of the trials performed. N = 120 female flies.