The physicist and mathematician Freeman Dyson once noted, “New directions in science are launched by new tools much more often than by new concepts.” This week marks the publication of a new tool that may alter the way we look at the brain. Karl Deisseroth and his colleagues at Stanford University have developed a method they call CLARITY. Yes, CLARITY is an acronym, for Clear Lipid-exchanged Anatomically Rigid Imaging/immunostaining-compatible Tissue hYdrogel.
By replacing the brain’s fat with a clear gel, CLARITY turns the opaque and impenetrable brain into a transparent and permeable structure. Most important, the hydrogel holds the brain’s anatomy intact. And because the hydrogel is permeable, the brain can be stained to localize proteins, neurotransmitters, and genes at a high resolution (see images below). Unlike other recent breakthroughs in neuroanatomy, this one can be used in human brains.
This technique is only for post-mortem tissue. And it measures structure not function. But I predict this new tool will revolutionize neuropathology, opening a new era for studying the neural basis of mental disorders. Indeed, in this initial report Deisseroth and his colleagues describe findings from a brain of someone who had died with autism 6 years earlier. With CLARITY they detected an unusual pattern of bridging connections from a particular class of inhibitory cells in this brain. Of course, this finding from a single brain needs to be replicated. The beauty of CLARITY is that other brains can now be tested, even tissue that has been stored for years.
by Thomas Insel, NIMH