Image from The New York Times
Photo Credit: David Lyon and Edward Callaway
Using a modified form of the Rabies virus, a team of scientists was able to isolate a single neuron (shown above in red) and those connected directly to it (shown above in yellow). Neuroscientists have been frustrated for decades by their inability to observe only the neurons connected to a single neuron.
It explains on The New York Times website:
Francis Crick, who turned his attention to neuroscience after his seminal work on the structure of DNA, once wrote that a critical tool the field was still lacking was "a technique for injecting a single neuron in such a way that all the neurons connected to it (and only those) are labeled." Recently, a group of scientists have transformed the rabies virus into a tool to accomplish just this — by harnessing the virus's lethally efficient natural mechanisms and turning it around to address Crick's challenge. Here, his single neuron is in red and the ones connected to it are in yellow.
See the rest of the slide-show and learn more about the book here.