Google and Harvard researchers present the most detailed map of the human brain to date

To create the new map, described in the journal Science, the researchers had to overcome several difficulties, including tracing the connections between neurons. In the outer layer of the brain alone there are about 16 billion neurons connected to each other by hundreds of billions of synapses. One neuron can connect to several thousand axons to (receive and) send information to thousands of other neurons. This makes constructing a connectome extremely difficult for even a very small part of the brain. The second challenge was obtaining a high-quality, reasonably well-preserved sample of brain tissue. However, given that the brain deteriorates very quickly after autopsy, cadaveric samples were out of the question. To overcome this obstacle, the team was lucky enough to obtain a fresh one-cubic-millimeter sample from the anterior temporal lobe of a patient with epilepsy. The fragment was removed during surgery to reduce seizures. The sample was then treated with resin and cut into several layers, which were examined using a high-speed electron microscope built specifically for this project.