Figure 56. Central complex (CX) to CX connections in the gall (GA), bulb (BU), round body (ROB) and rubus (RUB).

(A) Downstream synapses of potential CX output neurons, colored by the fraction of their target pathways that contribute to pathways coming back to the CX (see Materials and methods). The GA, BU, ROB, and RUB contribute most of their outputs to the CX and the lateral accessory lobe (LAL) almost none, while the upper neuropiles are mixed. (Ai) Frontal view; (Aii) side view. (B) Pathway weights of all pathways that start in the GA, BU, ROB, and RUB and end on another CX neuron. The weights are normalized for each type of origin. If the normalized pathway weight is 1, it corresponds to a neuron for which all output pathways come back to the CX. Connections are separated by the supertypes that these recurrent pathways reach. EB neurons mostly reach other EB neurons, whereas FB neurons mostly reach other FB neurons. (C) Morphological renderings of seven selected neuron types that innervate the GA, gall surround (GAs), ROB, and RUB. (Ci) Closeup of the four structures. (Cii) Illustration of the full morphology of the seven neuron types, showing the left population only. (D) Connectivity matrix of neurons that arborize in the right GA and GAs region. All connections outside of the CX regions (ellipsoid body [EB], protocerebral bridge [PB], fan-shaped body [FB], noduli [NO]) were considered because the GA region of interest does not capture the GAs. PFGs neurons were included in the analysis, but did not make any significant connections. (E) Illustration of selective connectivity between EPG neurons to PEG neurons from odd and even wedges of the EB in the dorsal and ventral GA, respectively. Left: schematic. Middle: rendering of EPG cells targeting the right GA with those from odd wedges colored in orange and those from even wedges colored in brown. Right: rendering of PEG neurons shown analogously as EPG cells (maroon: even-numbered PB glomeruli; pink: odd-numbered PB glomeruli). (F) Connectivity graphs on the level of neuron types showing any connections with at least 0.05 relative weight. (Fi) Connectivity in the GA and GAs. (Fii) Connectivity in the EB between the same neuron types as in (Fi), including the neurons from the other hemisphere.

Figure 56—figure supplement 1. Gall (GA) and gall surround (GAs).

(A) Neuron-to-neuron connectivity matrix of all neurons that make connections in the right GA. (B) Neuronal profiles of PFGs, EL, and PEG neurons in the electron microscopy (EM) micrographs taken from the fan-shaped body/ellipsoid body (FB/EB) regions (left panels) and the GA/GAs output terminal regions (right panels). The presynaptic densities that are observed for PFGs and EL neurons (circled in white) are not traditional T-bar-style synapses, while those in PEG neurons have clear T-bars (white arrowheads). Dense-core vesicles (DCVs) in PFGs and EL neurons are larger than those in PEG (yellow arrows). The fills correspond to the neuron segmentation. Scale bars: 500 nm. (C) Zoom in on a non-T-bar synapse (top), and a T-bar synapse next to a dense core vesicle (bottom). Views correspond to the areas in dashed rectangles in (B). Scale bars: 200 nm. (D) Table summarizing the finding of DCVs and synapse types for various output neurons.

Figure 56—figure supplement 2. Round body (ROB).

(A) Neuron-to-neuron connectivity matrix of PFR-to-PFR connections in the round body. PFR_b neurons contact both PFR_a neurons and themselves in the ROB in a homogeneous manner. (B) Connectivity graph of output pathways from PFR_a and PFR_b. (C) Morphological rendering of LAL002_R, the only non-central complex (non-CX) neuron targeting the ROB in a very targeted manner, and the main relay for PFR_b outputs.

Figure 56—figure supplement 3. FR connectivity in the rubus (RUB).

(A) Neuron-to-neuron connectivity matrix of FR-to-FR connections in the RUB. FR1 neurons form all-to-all connections between themselves, FR2 is not involved in direct central complex (CX) to CX connections in the RUB. (B) Neuron-to-neuron connectivity matrix of non-CX targets of FR neurons in the RUB. FR1 and FR2 neurons have largely different targets. (C) Connectivity graph of output pathways from FR1 and FR2.