What do the mushroom bodies do for the insect brain? Twenty-five years of progress

Abstract

In 1998, a special edition of Learning & Memory was published with a discrete focus of synthesizing the state of the field to provide an overview of the function of the insect mushroom body. While molecular neuroscience and optical imaging of larger brain areas were advancing, understanding the basic functioning of neuronal circuits, particularly in the context of the mushroom body, was rudimentary. In the past 25 years, technological innovations have allowed researchers to map and understand the in vivo function of the neuronal circuits of the mushroom body system, making it an ideal model for investigating the circuit basis of sensory encoding, memory formation, and behavioral decisions. Collaborative efforts within the community have played a crucial role, leading to an interactive connectome of the mushroom body and accessible genetic tools for studying mushroom body circuit function. Looking ahead, continued technological innovation and collaborative efforts are likely to further advance our understanding of the mushroom body and its role in behavior and cognition, providing insights that generalize to other brain structures and species.

Figure 1.

The Drosophila mushroom body. The mushroom body is a paired central brain area consisting of ∼2000–3000 neurons, termed Kenyon cells, whose dendrites reside in the calyx and whose axons form parallel bundles which make up the three main lobes: the horizontal γ-lobe, bifurcating and α′-lobes, and β and β′-lobes.

Figure 2.

Technology and advances in mushroom body research. Technological innovation often precedes major advances in our understanding of the structure and function of the mushroom body. Advances in microscopy, genetics, and computation have driven progress in our understanding of how the mushroom body develops and changes with an animal's experience. Open access resources have played a large role in progress: Online databases of Drosophila brain sections (https://jfly.uni-koeln.de/html/figures/Brain_K_Ito/brain_k_ito.html), fluorescent GAL4 patterns of Drosophila neurons (https://www.janelia.org/project-team/flylight [Jenett et al. 2012; Aso et al. 2014a]), available cell-type–specific drivers (https://bdsc.indiana.edu), connectomes (https://blog.flywire.ai [Zheng et al. 2018; Dorkenwald et al. 2022], https://www.janelia.org/project-team/flyem/hemibrain [Li et al. 2020], http://docs.neurodata.io/bilateral-connectome/define_data.html [Winding et al. 2023]), and platforms that connect identified connectome neurons to existing Drosophila resources (https://www.virtualflybrain.org [Court et al. 2023], https://neuronbridge.janelia.org [Meissner et al. 2023]) have allowed all researchers access to valuable resources, driving innovation through collaboration. Predicted future directions involve understanding the circuit basis of behavior with high resolution, biological validation of computational models to predict behavior (Gkanias et al. 2022), and using Drosophila to model neurological pathologies.