Nanoscopy in a Living Mouse Brain

Cells, the functional units of life, are beststudied in vivo. This is particularly truefor neurons, which perform their basic function of information processing by connect-ing with their neighbors. Therefore, unraveling the inner workings of the brain requires the im-aging of neurons in the living animal. Although confocal and multiphoton microscopy can vi-sualize neurons tagged with fluorescent proteins in transgenic living systems, they cannot discern features closer than half the wavelength of light (200 to 300 nm) (1). By causing such features to fluoresce sequentially, stimulated emission de-pletion (STED) microscopy and other emerging superresolution techniques have now overcome this barrier (2). Whereas these techniques have been applied throughout the life sciences, in viv