Neural drift during rest drives walking direction and memory consolidation in Drosophila

Heading is represented in head direction systems across species, including Drosophila. However, how navigation decisions are made and how goal memories are maintained, particularly during rest, is little understood. Here, using a navigation learning assay for flies walking in virtual reality, we describe neural dynamics for direction selection and memory. Activity of a subset of neurons in the fan-shaped body, a navigation and memory-related structure, continually drifts when the animal is at rest, centered 180 degrees opposite to the walking direction. Optogenetic activation during rest biases subsequent walking direction. Learning shifts rest activity, revealing a memory of goal direction. Downstream neurons correct the 180 degree shift, reactivating walking directions during rest; the connectome reveals a compact circuit consistent with reactivation, validated by computational modeling. Thus, rest activity drives behavior, reactivates walking directions, and is shaped by memory, suggesting shared principles for memory consolidation in navigation circuits across species.