We have previously demonstrated that individual Kenyon cells of the mushroom body receive input from an apparently random set of glomeruli, seven on average. The glomeruli connected to a given Kenyon cell share no common biological features and the projection neurons detecting odors as diverse as pheromones and food smells often converge on individual Kenyon cells. Such random connections probably serve to maximize the memory function of the mushroom body, and may be a fundamental property of certain brain centers also in vertebrates. How such random connections are established during development is not known. This is one question our lab is actively investigating.
Despite the randomness, not all glomeruli are equal: some glomeruli make more connections to Kenyon cells than others, for instance DA1, a glomerulus activated by the pheromone 11-cis-vaccenyl acetate. This bias may reflect the lifestyle of a species. Connections to a glomerulus involved in detecting an important odor, such as that of a fruit, pathogen or pheromone, might become overrepresented or underrepresented during evolution. Our lab is investigating whether and how structured and unstructured wiring strategies emerge during evolution in different fly species.