252 — Synaptic circuits and their variations within different columns in the visual system of Drosophila

This is one of the seminal connectomics papers and I wanted to be sure I got a chance to read it as one of my 365.

The columnar medulla that sits behind the fly’s eye acts as a sort of first-pass visual area, representing highly stereotyped circuitry (an analogue of what we might expect to see in mammalian visual cortex).

In this research, Takemura et al sample from seven of these columns, densely reconstructing the neural circuitry at a synaptic level. This enabled them to determine which cells in the circuit were consistent between columns, and where were not (which further informs the stereotypy measures between animals, in future research).

One particularly salient point is this first sentence of the Results section:

Reconstruction of a single circuit cannot differentiate between wiring errors, reconstruction errors, and natural variations.

This is hugely important not just for this paper, but for all of neural circuit reconstruction work, in any brain, in any animal.

The researchers used seven columns because these columns tile hexagonally; so in total, this research recorded and reconstructed a Home column, as well as its (hexagonal) six direct neighbors.

This enabled them to look at discrepancies between the columns, characterizing them as reconstruction errors or variations on the columnar circuit theme. Additionally, it informed new conclusions about proposals such as Peter’s Rule, which suggests that shared surface area between two cells correlates positively with the synapse count between them.