A new process that makes brain tissue transparent allows scientists to study whole brains in detail, without having to slice them apart.
Typically, in order to examine the deeply buried structures in the post-mortem brain, scientists must cut the tissue into extremely thin slices. While this can reveal cells and neurons, it makes it impossible to follow the circuitry through the brain's complex architecture.
Working with mouse brains, researchers at Stanford University injected a clear substance called a hydrogel, which attaches to everything but the lipids, or fats, in the brain's biochemistry. When the lipids were washed out with the help of a soapy solution and an electric current, the gel remained, holding all the brain's important structures intact and in place. Researchers then could infuse chemicals or dyes to target specific structures and neural circuits, and analyze the details in three dimensions. The dye can be flushed away and the brain can be tested again, with no deterioration.
The technique works in a human brain that has been preserved in formalin for years, meaning long-stored human brains now can be studied anew.
Researchers say the transparency process, which they call CLARITY, could help uncover the physical underpinnings of devastating mental disorders like schizophrenia, autism, post-traumatic stress disorder and others.
Details of their work are described in an article in the journal Nature.
Although CLARITY is not part of the Obama administration's recently unveiled initiative to unlock the mysteries of the human brain, the Nature article's senior author, Stanford researcher Dr. Karl Deisseroth, has been closely involved in creating and planning that initiative. And Dr. Thomas Insel, director of the National Institute of Mental Health, which helped fund the initiative, told The New York Times that CLARITY will help to build an anatomical "foundation" for the new brain research project.