Today, we return to the lab of neuroscientist Li-Huei Tsai, which brought us one of our favorite stories from four years ago - about the power of flashing lights on an Alzheimer’s-addled (mouse) brain. In this update, Li-Huei tells us about her team’s latest research, which now includes flashing sound, and ways in which light and sound together might retrieve lost memories. This new science is not a cure, and is far from a treatment, but it’s a finding so … simple, you won’t be able to shake it. Come join us for a lab visit, where we’ll meet some mice, stare at some light, and come face-to-face with the mystery of memory. We can promise you: by the end, you’ll never think the same way about Christmas lights again. Or jingle bells. This update was reported by Molly Webster, and produced by Rachael Cusick. The original episode was produced by Annie McEwen, Matt Kielty, and Molly Webster, with help from Simon Adler.  Special thanks to Ed Boyden, Cognito Therapeutics, Brad Dickerson, Karen Duff, Zaven Khachaturian, Michael Lutz, Kevin M. Spencer, and Peter Uhlhaas. Support Radiolab by becoming a member today at Radiolab.org/donate.     Molly's note about the image: Those neon green things in the image are microglia, the brain’s immune cells, or, as we describe them in our episode, the janitor cells of the brain. Straight from MIT’s research files, this image shows microglia who have gotten light stimulation therapy (one can only hope in the flicker room). You can see their many, super-long tentacles, which would be used to feel out anything that didn’t belong in the brain. And then they’d eat it! Further reading:  Li-Huei and co’s gamma sound and light paper: Multi-sensory Gamma Stimulation Ameliorates Alzheimer’s-Associated Pathology and Improves Cognition