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BrainBows: Neurons in the hippocampus, a brain area involved in memory, are labeled in different colors, with their neural projections pointing downward.
Credit: Tamily A. Weissman
In experiments so far, Lichtman's group has used the technology to trace all the connections in a small slice of the cerebellum, the part of the brain that controls balance and movement. Other scientists have already expressed interest in using the technology to study neural connections in the retina, the cortex, and the olfactory bulb, as well as in non-neural cell types.
Generating maps of even a small chunk of the brain will be a huge challenge: the human brain consists of an estimated 100 billion neurons, with trillions of synapses. Scientists will need to find ways to store, annotate, and mine the volumes of data they create, and to meld information about connectivity with findings about the molecular and physiological characteristics of neurons in the circuits. But now, at least, they have a key tool with which to begin the massive effort of creating a wiring diagram of the brain.