Max Planck Institute (MPI) for Medical Research scientists are developing a complete circuit diagram of the brain of the mouse using an electron microscope to make fine extensions of almost every single neuron visible.
Most axons are less than one micron thick, some even smaller than 100 nanometers. “The electron microscope is the only microscope with a high enough resolution to enable individual axons lying next to each other to be distinguished from each other,” says MPI scientist Winfried Denk.
In 2004, scientists working with Denk developed a new method that enabled “serial block-face” scanning electron microscopy. To examine tissue using this method, it must be fixed, stained and embedded in synthetic material.
This works for small pieces of tissue, but up to now it was not possible for tissue the size of a mouse brain.