Extended Data Figure 5: Connectomics analysis of inputs to PFNd and PFNv neurons.

a. Distribution of input synapses onto PFNd neurons from the hemibrain connectome²⁴, grouped by cell type. Shown are the top ten cell type inputs onto PFNd neurons; all other identified cell types are grouped into “Other.” Collectively, the distribution shown comprises 94.2% of all input synapses onto PFNd neurons. Numbers indicate the percentage of synapses contributed by each input cell type. Note that Δ7 neurons and FB3A/4C/4M neurons are major inputs to PFNd neurons, but we did not screen these neurons as part of our search for the origin of body-centric velocity signals in PFNd neurons, for the following reasons:

Δ7 neurons: Δ7 population activity is known to encode the fly’s heading direction, reflecting the strong input to Δ7 neurons from EPG neurons. It has been proposed that the function of Δ7 neurons is to reshape the heading bump into a cosine-shaped activity profile^5,34. Thus, much of the “compass input” that we refer to in our study as originating from EPG neurons is probably due to the combined action of EPG neurons (which constitute the primary computational map of the compass system) and Δ7 neurons (which reshape and reinforce the compass system output).

FB3A/4C/4M neurons: These neurons are FB tangential cells, meaning their axons run across the entire horizontal extent of the FB, perpendicular to PFNd dendrites⁵. Like other FB tangential cells, these neurons receive input from outside the central complex and they synapse onto a variety of cell types in the FB. There is evidence that FB tangential cells encode information about context, behavioral state, and internal physiological needs, including the need for sleep⁵.

b. Input connectivity matrix for PFNd neurons, shown for the top ten input cell types. Connections comprising 3 or fewer synapses are not shown. Note that the cell types that provide major unilateral input to PFNd neurons are LNO2, IbSpsP, EPG, SpsP, and LNO1.

c. Same as (a) but for PFNv neurons. Collectively, the distribution shown comprises 93.1% of all input synapses onto PFNv neurons.