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#inizurich

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Albert Cardona

"Theoretical principles explain the structure of the insect head direction circuit" by Pau Vilimelis Aceituno et al. 2024 from #INIZurich
elifesciences.org/articles/915

Loved the ending of the discussion, on why the head-direction circuit is organised in 8 columns:

"not all numbers of neurons enable a working circuit. The circuits for N=2 and N=4 are degenerate – either producing a single dimensional encoding, or two disconnected circuits that do not enforce the required circular topology. N=8 is the smallest power of two that could result in a non-degenerate circuit. This hints at the possibility that the eight-column architecture is not a chance evolutionary artefact, but rather that it is the genetically simplest circuit capable of performing heading integration."

Comparison to biological data. The biological network models of (A) the locust and (B) the fruit fly, with four distinct neural populations each were simplified to equivalent networks with one population by counting paths of lengths 1, 2, and 3 between EPG neurons (which encode the integrated heading) and using the net signed path count as a proxy for connectivity strength. The average connectivity profile for each neuron to its neighbours around the ring was compared to the sinusoidal connectivity predicted by our theory. The locust network has no standard deviation because the data in Pisokas et al., 2020, are based on light microscopy which couldn’t resolve variations between columns. Excitatory connections are shown in red and inhibitory connections in blue, while the strength of a connection is indicated by the line width.
Requirements for a heading integration circuit. 1. Circular topology: The activity should have the same topology as the variable it is encoding to prevent discontinuities. To encode heading, the activity should have the topology of a 1D circle. 2. Rotational symmetry: The heading integration circuit should work similarly, irrespective of the direction in which the insect travels. There should not be a bias for any direction. 3. Noise minimisation: The circuit should minimise the noise of the neural representation so the insect can navigate as precisely as possible.
#neuroscience#Drosophila#locust
Public
Albert Cardona

"we illustrate that in our theory, the consistent presence of the eight-column organisation of head direction circuits across multiple insect species is not a chance artefact but instead can be explained by basic evolutionary principles."

Interesting take on possible constraints that defined the circuit architecture of the #Drosophila central complex in its role as a brain centre for spatial navigation.

"The insect compass system: From theory to circuitry", by Pau Vilimelis Aceituno et al. 2023 at #INIZurich biorxiv.org/content/10.1101/20

bioRxiv · The insect compass system: From theory to circuitryTo navigate their environment, insects need to keep track of their orientation. Previous work has shown that insects encode their head direction as a sinusoidal activity pattern around a ring of neurons arranged in an eight-column structure. However, it is unclear whether this sinusoidal encoding of head direction is just an evolutionary coincidence or if it offers a particular functional advantage. We address this question by establishing the basic mathematical requirements for direction encoding and show that several potential circuits with different activity patterns can perform the same function. We prove that among these activity patterns, the sinusoidal one is the most noise-resilient, but only when coupled with a specific connectivity pattern between the encoding neurons. We compare this optimal connectivity pattern with experimental data from the head direction circuits of the locust and the fruit fly, finding a remarkable agreement between our theory and experimental evidence. Furthermore, we demonstrate that our predicted circuit can emerge naturally using Hebbian plasticity, which means the neural connectivity does not need to be explicitly encoded in the genetic program of the insect but rather can emerge during development. Finally, we illustrate that in our theory, the consistent presence of the eight-column organisation of head direction circuits across multiple insect species is not a chance artefact but instead can be explained by basic evolutionary principles. ### Competing Interest Statement The authors have declared no competing interest.
#neuroscience#CentralComplex
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