Opening the black box to see how brains perform path integration (PI) is out of reach of our current techniques. To better understand fundamental processes like path integration requires a creative touch with analytical and experimental approaches; Rob Vickerstaff and Allen Cheung have taken a modelling approach to their studies of PI. By assessing the impact of noise on various models of PI, they are able to rate the robustness of various co-ordinate frames for PI – surely a major factor in rating their biological plausibility.
Cheung A, Vickerstaff R, 2010 Finding the Way with a Noisy Brain. PLoS Comput Biol 6(11): e1000992. doi:10.1371/journal.pcbi.1000992
A recurring theme of posts here is that an understanding of behaviour requires knowledge of (amongst other things) the sensory apparatus available to the navigating animal. Ugolini et al add to their extensive studies of the Sandhopper with a characterisation of the spectral photoresponses of its compound eyes. A strong UV-blue sensitivity is confirmed, which may be the channel for celestial compass information. Allied with a green channel, this is likely to provide the sandhopper with a visual system ideally suited for identifying terrestial landmarks, the use of which has been previously demonstrated by this group.
Ugolini A, Borgioli G, Galanti G, Mercatelli L, Hariyama T. (2010) Photoresponses of the compound eye of the sandhopper Talitrus saltator (Crustacea, Amphipoda) in the ultraviolet-blue range. Biol Bull. 2010 Aug;219(1):72-9.
Being able to genetically dissect the brain process and structures involved in insect spatial behaviour would be a massive opportunity for our research field. This research requires the correct behavioural assays to probe spatial behaviour and it is this endeavour that leads Foucaud et al (2010) to develop an analog of the water maze for Drosophila.
Foucaud J, Burns JG, Mery F (2010) Use of Spatial Information and Search Strategies in a Water Maze Analog in Drosophila melanogaster. PLoS ONE 5(12): e15231. doi:10.1371/journal.pone.0015231
There is a gap in the literature between insect and vertebrate navigation. This gap seems to result more from the use of different approaches and a lack of comparative studies than from actual differences in the animals’ navigational mechanisms. The recent study of Pecchia et al. provides a bridge between vertebrate and insect cognition by demonstrating the use of an egocentric view-based strategy in chicks.
The authors trained chicks to relocate a reward within a rectangular array of 4 cylindrical landmarks. The reward was located inside one of the landmarks and could be reached through a head-sized circular opening in the cylinder. Chicks could learn the spatial arrangements of the landmark scene as long as the circular opening pointed in the same direction throughout training, but failed if the circular opening was rotated around the rewarded landmark from trial to trial. Interestingly, the learning of the rewarded landmark identity was not affected by such rotation of the circular opening. The authors conclude that a stable view at the goal is required for “place navigation” (i.e., learning of the landmarks’ spatial arrangement) but not for “non-spatial learning” (i.e., individuallandmark recognition). Post by Antoine Wystrach
Pecchia, T. and Vallortigara, G. (2010). View-based strategy for reorientation bygeometry. J. Exp. Biol. 213, 2987-2996.
The cost of searching for an inconspicuous nest entrance in the scorching heat is all the incentive that a desert ant needs to rapidly learn any landmark information that is available. In this paper Wehner and Muller show how even a single pebble can decrease time spent searching for the nest by a factor of 5 or more. Wehner and Muller go on to investigate how searching time relates to the direction of nest approach when a nest is marked by two artificial cylinders. They find that searching time is lowest (i.e. most accurate return) when ants inbound route goes close to a landmark, thus generating the largest change in retinal appearance of the landmarks during the final approach. These final routes are smooth and the paper throws up fascinating questions about how smooth inbound routes might be guided by discrete views stored during the learning walks of these ants. The learning walks were described in a paper earlier in the year (re-posted below).
Rüdiger Wehner and Martin Müller (2010) Piloting in desert ants: pinpointing the goal by discrete landmarks J Exp Biol 213, 4174-4179
Muller and Wehner have described a fascinating behaviour in their recent Current Biology paper (“Path Integration Provides a Scaffold for Landmark Learning in Desert Ants”). Outbound foragers perform a series of pirouettes that seem structured in order to fixate their nest entrance.
Muller and Wehner (2010) Current Biology, Volume 20, Issue 15, 1368-1371,
As a follow up to the paper, Graham et al. discuss the ways that path integration and snapshots could be combined.
Here is a really useful paper that I missed earlier in the year: Sanes and Zipursky (2010) Design Principles of Insect and Vertebrate Visual Systems Neuron 66(1) 15-36. The authors look at the similarities between the early layers of visual processing in insects and vertebrates, suggesting that there is a large degree of phylogenetic conservation.
Abstract: “A century ago, Cajal noted striking similarities between the neural circuits that underlie vision in vertebrates and flies. Over the past few decades, structural and functional studies have provided strong support for Cajal’s view. In parallel, genetic studies have revealed some common molecular mechanisms controlling development of vertebrate and fly visual systems and suggested that they share a common evolutionary origin. Here, we review these shared features, focusing on the first several layers—retina, optic tectum (superior colliculus), and lateral geniculate nucleus in vertebrates; and retina, lamina, and medulla in fly. We argue that vertebrate and fly visual circuits utilize common design principles and that taking advantage of this phylogenetic conservation will speed progress in elucidating both functional strategies and developmental mechanisms, as has already occurred in other areas of neurobiology ranging from electrical signaling and synaptic plasticity to neurogenesis and axon guidance.”
Those malevolent creatures, the parasitoid wasps, need precise orientation in order to locate hosts, but the optimum strategies and the value of learning for a wasp may vary as a function of ecology. Hoedjes et al, in their recent review, suggest that this variation makes them an ideal model for studying the interaction between learning and ecology.
In the authors’ own words ” … …the neural and genetic pathways underlying learning and memory formation seem strikingly similar among species of distant animal phyla, several more subtle inter- and intraspecific differences become evident from studies on model organisms. The true significance of such variation can only be understood when integrating this with information on the ecological relevance. Here, we argue that parasitoid wasps provide an excellent opportunity for multi-disciplinary studies that integrate ultimate andproximate approaches.”
Hoedjes et al (2010) Natural variation in learning rate and memory dynamics in parasitoid wasps: opportunities for converging ecology and neuroscience PRSB
I imagine that everybody has a story about a particular experiment where the animals didn’t do the thing that was expected. Well, this paper shows how nice discoveries can still come from surprising outcomes. Desert ants were provided with prominent landmark information that predicted a successful exit direction from an arena. However, this information was not exploited by the ants. Rather, the experiments demonstrated another intriguing mechanism by which ants recalled arena-exit directions as local vectors dependent on context provided by the arena.
Legge, E.L., Spetch, M.L., & Cheng, K. (2010). Not using the obvious: desert ants, Melophorus bagoti, learn local vectors but not beacons in an arena. Animal Cognition. 13, 849-860