Event:

Working memory - the ability to keep information in mind for short periods of time - is a central building block of cognition, thought to be produced by cortical circuits and exclusive to mammals. Our work challenges this idea. We discovered that larval zebrafish, an animal with no cortex, keep directional information in memory to decide where to escape. Surprisingly, larvae share with mammals many of the key features of working memory. Similar to primates, they store memories up to 10s. Also, larvae reset the memory after escaping, showing that information is selected to be used for specific decisions. Finally, fish average information from distinct cues, suggesting that they can manipulate working memories. But, how is working memory stored in the larval brain?
To answer this question, we built a light-sheet microscope to perform brain-wide calcium imaging in larvae performing the working memory assay and mapped brain areas whose activity correlates with different features of the assay. In particular, we found neurons in the hindbrain oscillator that show persistent activity during the delay period, with a timescale matching that of working memory, and whose activity is reset after decision. Our results demonstrate the usefulness of zebrafish larvae as a model for the study of the subcortical brain regions involved in working memory.