 This tiny brain structure is known as the claustrum. For more than a hundred years, scientists have speculated about what exactly the claustrum does. But only recently has state-of-the-art biological technology allowed researchers to probe its anatomy and connections to the rest of the brain. Francis Crick, of DNA fame, and neuroscientist Christophe Koch hypothesized the claustrum to be the seat of consciousness, a conductor of sorts, orchestrating the activity of neurons in charge of higher brain functions from deep within. Now, new research from Rekin's Center for Brain Science in Japan appears to confirm that hypothesis. Only instead of arousing neurons to action, the claustrum lulls them to sleep. The claustrum is both an appropriate and unfortunate name for this important part of the brain's anatomy. Latin for hidden or shut away, the claustrum has long defied close examination due to its thin, irregular shape and placement deep within the brain. In fact, it was only by accident, or serendipity perhaps, that Rekin's scientist, Yoshihiro Yoshihara, stumbled upon the claustrum in action. Yoshihara and colleagues had initially set out to understand the science of smell using light to genetically visualize and manipulate neurons in the olfactory circuit of mice. But in one group of mice, that circuit unexpectedly went dark. Yoshihara briefly considered dismissing the negative findings, but ultimately chose to take a closer look. It turned out that instead of targeting olfactory neurons, Yoshihara's team had accidentally locked onto neurons in the claustrum. That unexpected discovery was followed by a series of much more unexpected results. The claustrum was found to be connected to neurons in the brain's cortex, the outer gray matter, part of the brain, in charge of various higher functions. But instead of activating them, as Crick and Koch had postulated, the claustrum silenced those neurons. The long period of silence induced by the claustrum is characteristic of slow waves in the brain, which occur during the deep sleep that precedes rapid eye movement sleep. That the claustrum coordinates this slow wave activity and does so broadly across large regions of the brain is critical. Probing this silencing function could help researchers better understand neural mechanisms underlying slow wave sleep. The Rekin team looks forward to further demystifying the workings of the elusive claustrum. In particular, the team plans to explore the role the claustrum plays in memory consolidation and consciousness.