Computation for navigation in the insect brain

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

Categories: Papers from 2017

Navigation in cockroaches

On this site we do have a bias towards social insects, but navigation is, of course, valuable for all insects. Some insects, like cockroaches, have a long history of neuroscientific investigation and in recent times, really exciting neuroscience has been showing the cellular basis of orientation in insects. In this review, Varga et al. review what we know about insect navigational circuits and they are compared to the well-studied cellular basis of navigation in rodents.
Abstract: “Cockroaches are scavengers that forage through dark, maze-like environments. Like other foraging animals, for instance rats, they must continually asses their situation to keep track of targets and negotiate barriers. While navigating a complex environment, all animals need to integrate sensory information in order to produce appropriate motor commands. The integrated sensory cues can be used to provide the animal with an environmental and contextual reference frame for the behavior. To successfully reach a goal location, navigational cues continuously derived from sensory inputs have to be utilized in the spatial guidance of motor commands. The sensory processes, contextual and spatial mechanisms, and motor outputs contributing to navigation have been heavily studied in rats. In contrast, many insect studies focused on the sensory and/or motor components of navigation, and our knowledge of the abstract representation of environmental context and spatial information in the insect brain is relatively limited. Recent reports from several laboratories have explored the role of the central complex (CX), a sensorimotor region of the insect brain, in navigational processes by recording the activity of CX neurons in freely-moving insects and in more constrained, experimenter-controlled situations. The results of these studies indicate that the CX participates in processing the temporal and spatial components of sensory cues, and utilizes these cues in creating an internal representation of orientation and context, while also directing motor control. Although these studies led to a better understanding of the CX’s role in insect navigation, there are still major voids in the literature regarding the underlying mechanisms and brain regions involved in spatial navigation. The main goal of this review is to place the above listed findings in the wider context of animal navigation by providing an overview of the neural mechanisms of navigation in rats and summarizing and comparing our current knowledge on the CX’s role in insect navigation to these processes. By doing so, we aimed to highlight some of the missing puzzle pieces in insect navigation and provide a different perspective for future directions.”
Varga, A. G., Kathman, N. D., Martin, J. P., Guo, P., & Ritzmann, R. E. (2017). Spatial Navigation and the Central Complex: Sensory Acquisition, Orientation, and Motor Control. Frontiers in Behavioral Neuroscience11.
Categories: Papers from 2017

How to interpret interactions between PI and vision

The classic components of the insect navigation toolkit are Path Integration and guidance by learnt visual cues. We know that the interaction between these cues is not a simple hierarchy. Both can be active at the same time and there are interesting interactions when ants are moved to a visually novel location with a Path Integration home vector. Ants will follow the direction of their PI home vector for a while before starting to search. The distance for which ants follow their PI vector is greater for species that live in environment with reduced visual information (like a desert for instance). In this paper, Freas et al. investigate the insect navigational toolkit with a nocturnal ant. These ants are shown to use PI and visual information and in tests where they are put in novel environment with a full PI vector, they follow it for a short distance before searching. This demonstrates the value of visual information, even in a nocturnal species.

Freas, C. A., Narendra, A., & Cheng, K. (2017). Compass cues used by a nocturnal bull ant, Myrmecia midas. Journal of Experimental Biology, jeb-152967.

Categories: Papers from 2017

Visual navigation in dim light

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.”

Categories: Papers from 2017

Path Integration on a track-ball

Across many areas of neuroscience and neuroethology, track balls have been used to allow close inspection of behaviour in animals that think they are freely-moving. This paper shows a really elegant solution for ants. Using a tether that allows the ant to rotate, then allows ants to perform naturalistic path integration with accurate direction, length and search phases. This techniques is going to be crucial in the fine-study of navigation behaviours.
Hansjürgen Dahmen, Verena L. Wahl, Sarah E. Pfeffer, Hanspeter A. Mallot, and Matthias Wittlinger (2017) Naturalistic path integration of Cataglyphis desert ants on an air-cushioned lightweight spherical treadmill. J Exp Biol 2017 220:634-644. doi:10.1242/jeb.148213
Categories: Papers from 2017

Mushroom Body Modelling

These papers might not be concerned with navigation directly, but they are both nice examples of how computational modelling can help us pursue a bottom-up approach to understanding the insect brain. Behavioural experiments investigating learning often result in descriptions of the “cognitive” capabilities of insects. However, without mechanistic grounding, the follow-up to these papers can often be semantic bickering or a contrarian attempt to think of different experimental stimuli, that might offer a different conclusion. With modelling one can at least demonstrate how certain “cognitive” properties can emerge from a particular architecture.
Here we have two papers from Lars Chittka’s group. Both take biological realistic models of the nervous architecture of insect and simulate a learning paradigm. Without specific tuning of the models, we see emergent properties. In simulations of olfactory experiments (Peng and Chittka) the network naturally shows peak shift and can deal with positive and negative patterning. In the visual domain (Roper et al.) we see visual generalisation and location invariance.
Peng, F., & Chittka, L. (2016). A Simple Computational Model of the Bee Mushroom Body Can Explain Seemingly Complex Forms of Olfactory Learning and Memory. Current Biology.
Roper, M., Fernando, C., & Chittka, L. (2017). Insect Bio-inspired Neural Network Provides New Evidence on How Simple Feature Detectors Can Enable Complex Visual Generalization and Stimulus Location Invariance in the Miniature Brain of Honeybees. PLOS Computational Biology13(2), e1005333.
Categories: Papers from 2017

Natural Experiments

How does the ecological niche of a species affect cognitive abilities? This is a hard question to answer, but occasionally there is a “natural experiment” waiting that can help with this. Here we have a pair of closely related ant species living in the same trees, but with different foraging style – how does this affect navigation skills?
Abstract: “Cognitive abilities evolve by natural selection to help an organism cope with problems encountered in the organism’s typical environment. In acacia ants, coevolution with the acacia tree led workers to forage exclusively on the host plant (“in-nest” foraging), instead of the central-place foraging typical for most social insects. To test whether foraging ecology altered the orientation skills of acacia ants, we developed a novel field disorientation assay to evaluate the ability of foraging workers to quickly reorient after being disoriented (rotated) in an experimental arena. We compared 10 behaviors among disoriented and sham-treated workers of three in-nest foraging species (Pseudomyrmex nigrocinctus, P. flavicornis, and P. spinicola) and two central-place foraging species that regularly forage off the host tree (P. gracilis, P. nigropilosus). We predicted that experimental disorientation of workers should affect in-nest foraging species (acacia ants) more than central-place foraging species. Behavioral differences between control and disoriented ants were not consistently associated with foraging ecology, although the species least able to recover after disorientation was an acacia ant (P. nigrocinctus), and the species performing best after disorientation was a central-place forager (P. gracilis). Only one of the 10 behaviors studied consistently differed in experimentally disoriented workers compared to controls in all three species of acacia ants, whereas none of the experimentally disoriented central-place foragers differed from control workers for this specific behavior. Future studies could evaluate additional ant species living in obligate associations with plants, to further compare the cognitive abilities of in-nest versus central-place foraging organisms.”

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.

Categories: Papers from 2017