Structured Connectivity Across Multiple Drosophila Mushroom Bodies

In the world of learning and memory, neural circuits exhibit plasticity, yet the extent to which their architecture is consistent remains a mystery. Random connections might enhance stimulus discrimination, but structured connections could better direct behaviorally relevant information. Researchers have now compared five adult Drosophila melanogaster Mushroom Body hemispheres from three connectomes, establishing a unified framework for uniglomerular projection neurons, Kenyon Cells, Mushroom Body Output Neurons, and Lateral Horn Centrifugal Neurons.

Despite differences in Kenyon Cell abundance and detailed connections, they found that the organization of uniglomerular projection neurons to Kenyon Cells and Kenyon Cells to Mushroom Body Output Neurons remained consistent. This consistency was observed in food-associated projection neuron channels, which consistently connected a higher proportion of Kenyon Cells than would be expected by chance.

Furthermore, this preference was seen as being directed towards approach-promoting Mushroom Body Output Neurons. Even the sensory input remained consistent across sister Mushroom Body Output Neurons from the same hemisphere, regardless of the individual Kenyon Cell partners. Lastly, recurrent feedback from the Lateral Horn Centrifugal Neurons, which were predicted to be inhibitory, also targeted Kenyon Cells receiving these food-associated inputs.

These findings demonstrate that a memory network can maintain local variability while also preserving structured pathways that prioritize ethologically relevant sensory information.