<i>Drosophila</i> maintain a consistent navigational goal angle for days to weeks

Past work has demonstrated that <i>Drosophila</i> can keep to a consistent navigational bearing for minutes to hours. Here, we ask whether they can do so over days to weeks. First, we describe an experimental rig that allows individual head-fixed <i>Drosophila</i> to live for at least two weeks within a virtual-reality environment. Flies walk on a spherical treadmill and receive sugar drops at defined moments as food. Individuals express robust circadian and sleep rhythms on these rigs. We further show that flies freely navigating an environment containing a single visual orienting cue (akin to the sun) will often pick a unique direction and walk forward along that direction for tens to hundreds of meters over days to weeks. This preferred direction can be considered a goal angle because individuals will repeatedly correct for experimentally induced virtual rotations away from this angle. Flies rely on the visual cue to effectively progress forward along the goal angle-walking in circles without it-and they return to walking forward along the same angle in the morning after spending a full night (twelve hours) in darkness without the cue. These results argue for the existence of navigation goals in the <i>Drosophila</i> brain with a persistence time of days to weeks. Furthermore, the technology introduced here may enable trained behaviors across thousands of reinforcement trials in <i>Drosophila</i>, a paradigm central to mammalian neuroscience yet absent in flies.