In Neural Migration, the artist and neuroscientist Greg Dunn depicts radial glia (black) creating new neurons (white). On page 26 , Charles Nicholson focuses not on brain cells but on the gaps between them. Unlike the vast open spaces shown on the cover, most extracellular space in real brain tissue is only tens of nanometers wide and thus difficult to probe. Diffusion analysis and imaging techniques have gradually been able to characterize that space, which is essential for passing electrical and chemical signals. (Neural Migration, 2021, Greg Dunn, www.gregadunn.com .)