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Optimal searching behaviour generated intrinsically by the central pattern generator for locomotion


Berni, Jimena; Sims, David W.; Humphries, Nicolas E. (2020), Optimal searching behaviour generated intrinsically by the central pattern generator for locomotion, Dryad, Dataset,


Efficient searching for resources such as food by animals is key to their survival. It has been proposed that diverse animals from insects to sharks and humans adopt searching patterns that resemble a simple Lévy random walk, which is theoretically optimal for ‘blind foragers’ to locate sparse, patchy resources. To test if such patterns are generated intrinsically, or arise via environmental interactions, we tracked free-moving Drosophila larvae with (and without) blocked synaptic activity in the brain, suboesophageal ganglion (SOG) and sensory neurons. In brain-blocked larvae we found that extended substrate exploration emerges as multi-scale movement paths similar to truncated Lévy walks. Strikingly, power-law exponents of brain/SOG/sensory-blocked larvae averaged 1.96, close to a theoretical optimum (µ = 2.0) for locating sparse resources. Thus, efficient spatial exploration can emerge from autonomous patterns in neural activity. Our results provide the strongest evidence so far for the intrinsic generation of Lévy-like movement patterns.


The exploratory behaviour was monitored using a Frustrated Total Internal Reflection (FTIR)-based Imaging Method for high throughput locomotion analysis. The 240 X 240 mm arena was coated with a 2 mm thick layer of 0.8% agar and placed within a temperature controlled LMS220 chamber in the dark at 22oC or at 33 ± 1 oC. In each trial we tracked 10 young third instar larvae (mean lenght, 2.37 mm ± 0.57 S.D.; n = 90) for 1 h at 2fps with a Basler acA2040-180km CMOS camera using Pylon and StreamPix software, mounted with a 16mm KOWA IJM3sHC.SW VIS-NIR Lens and 825nm high performance longpass filter (Schneider, IF-093). The x,y coordinates of individual larvae exploring the agar were obtained using the FIM track free software (Risse, B., Thomas, S., Otto, N., Löpmeier, T., Valkov, D., Jiang, X., Klämbt, C. FIM, a novel FTIR-based imaging method for high throughput locomotion analysis. PLoS ONE 8, e53963 (2013)). A simple linear smoothing was applied to remove the jaggedness of the track caused by the integer (pixel) based recording. To achieve this two 1D filters were used, one for movement in x and one for movement in y, with parameters for both as follows: position state minimum variance = 0.5; velocity state minimum vari- ance = 0.5; measurement covariance = 1.0. These parameters smoothed the track while introducing a minimum change to the track locations



Usage Notes

Details on genotypes and nomenclature are available in manuscript. 

Treatments and their corresponding track file names are shown in Supplementary file 3, which is included in dataset.

CSV files show x, y coordinates in mm at 2Hz (disregard time column) after the application of the Kalman processing. 

Files called "15Hz ..." were collected at 15Hz. 



Wellcome Trust, Award: 105568/Z/14/Z