The boutons that mark the end of one nerve almost touch the dendrites of the next nerve. But they don’t quite touch. “It takes a courageous person,” the poet Kay Ryan once wrote, “to leave spaces empty”—and Cajal, the draftsman-scientist, was anything but timorous. That space—about twenty to forty nanometers in distance—is left blank. It is tiny; you could wave it away. Perhaps it’s an artifact of microscopy or staining. But like the negative space in a Chinese painting, that space might represent the most important element of the whole drawing—and arguably, of the entire physiology of the
...more
