Have you ever wondered what happens in the brain during sleep? Or what regulates which substances can enter your brain and which can’t? When we think of the brain, we think of neurons. However, neurons can’t do all of this work by themselves! The cerebrospinal fluid (CSF) is a significant player in the brain and helps carry out vital functions, such as cleaning your brain during sleep! So why do we know so little about it? Learn more about the CSF and its fundamental roles in the brain with Dr. Madeline A. Lancaster, a Group Leader in the Cell Biology Division of the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, UK. She explains why we should pay more attention to the CSF and how, thanks to the recent in vitro models developed in her lab, we can now study this vital fluid like never before.