In recent years the central complex of insects has emerged as a particularly interesting brain area for those of us interested in spatial behaviours. Exciting neuroscience from flies has offered a tantalising glimpse of a future where we can describe the circuits that underpin navigation. To bring about that future we need a creative combination of behavioural, modelling, and neuroscience efforts. In this spirit, Cope et al., take recent neuroscience findings and produce a computational model which captures the way that visual cues can be used to maintain a sense of relative orientation.
Abstract: “The insect central complex (CX) is an enigmatic structure whose computational function has evaded inquiry, but has been implicated in a wide range of behaviours. Recent experimental evidence from the fruit fly (Drosophila melanogaster) and the cockroach (Blaberus discoidalis) has demonstrated the existence of neural activity corresponding to the animal’s orientation within a virtual arena (a neural ‘compass’), and this provides an insight into one component of the CX structure. There are two key features of the compass activity: an offset between the angle represented by the compass and the true angular position of visual features in the arena, and the remapping of the 270° visual arena onto an entire circle of neurons in the compass. Here we present a computational model which can reproduce this experimental evidence in detail, and predicts the computational mechanisms that underlie the data. We predict that both the offset and remapping of the fly’s orientation onto the neural compass can be explained by plasticity in the synaptic weights between segments of the visual field and the neurons representing orientation. Furthermore, we predict that this learning is reliant on the existence of neural pathways that detect rotational motion across the whole visual field and uses this rotation signal to drive the rotation of activity in a neural ring attractor. Our model also reproduces the ‘transitioning’ between visual landmarks seen when rotationally symmetric landmarks are presented. This model can provide the basis for further investigation into the role of the central complex, which promises to be a key structure for understanding insect behaviour, as well as suggesting approaches towards creating fully autonomous robotic agents.”
Cope AJ, Sabo C, Vasilaki E, Barron AB, Marshall JAR (2017) A computational model of the integration of landmarks and motion in the insect central complex. PLoS ONE 12(2): e0172325. doi:10.1371/journal.pone.0172325
Freas, C. A., Narendra, A., & Cheng, K. (2017). Compass cues used by a nocturnal bull ant, Myrmecia midas. Journal of Experimental Biology, jeb-152967.
The ability of insects to use visual information for navigation, even at very low light levels, shows the fundamental robustness of visual cues for navigation. In a special issue of Phil Trans, themed arounf vision in dim light, two papers show how insects use vision for navigation, even in the most testing circumstances.
Ajay Narendra and Fiorella Ramirez-Esquivel (2017) Subtle changes in the landmark panorama disrupt visual navigation in a nocturnal bull ant. Phil. Trans. R. Soc. B April 5, 2017 372 20160068; doi:10.1098/rstb
Abstract: “The ability of ants to navigate when the visual landmark information is altered has often been tested by creating large and artificial discrepancies in their visual environment. Here, we had an opportunity to slightly modify the natural visual environment around the nest of the nocturnal bull ant Myrmecia pyriformis. We achieved this by felling three dead trees, two located along the typical route followed by the foragers of that particular nest and one in a direction perpendicular to their foraging direction. An image difference analysis showed that the change in the overall panorama following the removal of these trees was relatively little. We filmed the behaviour of ants close to the nest and tracked their entire paths, both before and after the trees were removed. We found that immediately after the trees were removed, ants walked slower and were less directed. Their foraging success decreased and they looked around more, including turning back to look towards the nest. We document how their behaviour changed over subsequent nights and discuss how the ants may detect and respond to a modified visual environment in the evening twilight period.”
James J. Foster, Basil el Jundi, Jochen Smolka, Lana Khaldy, Dan-Eric Nilsson, Marcus J. Byrne, and Marie Dacke (2017) Research article: Stellar performance: mechanisms underlying Milky Way orientation in dung beetles. Phil. Trans. R. Soc. B April 5, 2017 372 20160079; doi:10.1098/rstb.2016.0079
Abstract: “Nocturnal dung beetles (Scarabaeus satyrus) are currently the only animals that have been demonstrated to use the Milky Way for reliable orientation. In this study, we tested the capacity of S. satyrus to orient under a range of artificial celestial cues, and compared the properties of these cues with images of the Milky Way simulated for a beetle’s visual system. We find that the mechanism that permits accurate stellar orientation under the Milky Way is based on an intensity comparison between different regions of the Milky Way. We determined the beetles’ contrast sensitivity for this task in behavioural experiments in the laboratory, and found that the resulting threshold of 13% is sufficient to detect the contrast between the southern and northern arms of the Milky Way under natural conditions. This mechanism should be effective under extremely dim conditions and on nights when the Milky Way forms a near symmetrical band that crosses the zenith. These findings are discussed in the context of studies of stellar orientation in migratory birds and itinerant seals.”
Amador-Vargas, S., & Mueller, U. G. (2017). Ability to reorient is weakly correlated with central-place versus non-central-place foraging in acacia ants. Behavioral Ecology and Sociobiology, 71(2), 43.