Circuit reorganization in the Drosophila mushroom body calyx accompanies memory consolidation

The formation and consolidation of memories are complex phenomena involving synaptic plasticity, microcircuit reorganization, and the formation of multiple representations within distinct circuits. To gain insight into the structural aspects of memory consolidation, we focus on the calyx of the Drosophila mushroom body. In this essential center, essential for olfactory learning, second- and third-order neurons connect through large synaptic microglomeruli, which we dissect at the electron microscopy level. Focusing on microglomeruli that respond to a specific odor, we reveal that appetitive long-term memory results in increased numbers of precisely those functional microglomeruli responding to the conditioned odor. Hindering memory consolidation by non-coincident presentation of odor and reward, by blocking protein synthesis, or by including memory mutants suppress these structural changes, revealing their tight correlation with the process of memory consolidation. Thus, olfactory long-term memory is associated with input-specific structural modifications in a high-order center of the fly brain. [Display omitted] •Synaptic microglomeruli linked to a specific odor can be identified in Drosophila•Microglomeruli represent complex microcircuits involving different types of neurons•Long-term memory results in increased microglomeruli in an input-specific manner•Newly formed microglomeruli participate in conditioned odor representation Baltruschat et al. investigate structural modifications upon memory consolidation in a center essential for olfactory memory in Drosophila, in which second- and third-order neurons connect via synaptic microglomeruli. Although short-term memory reveals no evidence of structural plasticity, appetitive long-term memory is associated with increased microglomeruli in an input-specific manner.