Marcel Sayre

Marcel Sayre

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    Many central place foragers, like bees and ants, have impressive navigational capabilities. Honeybees, bumblebees, and some solitary bees can travel distances in the tens of kilometres to unfamiliar areas and, despite the convoluted nature of their outbound path, return to their nest in a straight line. Many ant species are capable of similar navigational feats, often foraging in novel terrain at great distances relative to their size. What's fascinating about these insects is that this robust navigational behaviour is all computed within the confines of a brain that could fit on the tip of a pen. Compared to the roughly 80 billion neurons in the human brain, insect brains typically contain in the range 100,000 – 1,000,000 total neurons. Yet, despite this limitation insects exhibit remarkable navigational (and non-navigational) behaviours.

    Within the insect brain, an area known as the central complex (CX) houses circuits that compute navigational decisions. More specifically, overwhelming evidence suggests that the CX is a biological compass that integrates self-motion and context dependent cues to initiate steering and movement commands. Every insect studied to date has a CX which appears to be anatomically well conserved, even across insects that diverged hundreds of millions of years ago. Yet despite the conserved nature of the CX, many species of insects have been shown to use different strategies for navigating in their surrounding environments. How can such a seemingly conserved brain area give rise to such diverse navigational behaviour? 

    We are pursuing the answer to this question by comparing the circuitry underlying the CX across six species of bees and ants, each of which either has a different strategy of navigation (path integration, landmark navigation, pheromone tracking), or differs in its preferred mode of locomotion (flying versus walking). By tracing all major CX neurons across these species using block-face electron microscopy, we are delineating neural projection patterns, as well as establishing local connectomes of computational modules within the CX. This will illuminate the information flow within the CX and allow to construct anatomically constrained models of the fundamental computational processes in this brain region. With these neuroanatomical maps, we can intracellularly record from major CX neurons in species which show the most anatomically divergent traits. And by revealing the role of specific neural elements in the CX, we can lead the way in understanding how sensory information is transformed into behavioural decisions within the context of navigation.

    Keywords

    • connectomics
    • neuroscience
    • insect
    • navigation

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