Researchers from the Howard Hughes Medical Institute, Google and other institutions have published the neuron level connectome of a significant part of the brain of the fruit fly, what they called the hemibrain. This may become one of the most significant advances in our understanding of the detailed structure of complex brains, since the 302 neurons connectome of C. elegans was published in 1986, by a team headed by Sydney Brenner, in an famous article with the somewhat whimsical subtitle of The mind of a worm. Both methods used an approach based on the slicing of the brains in very thin slices, followed by the use of scanning electron microscopy and the processing of the resulting images in order to obtain the 3D structure of the brain.
The neuron-level connectome of C. elegans was obtained after a painstaking effort that lasted decades, of manual annotation of the images obtained from the thousands of slices imaged using electron microscopy. As the brain of Drosophila melanogaster, the fruit fly, is thousands of times more complex, such an effort would have required several centuries if done by hand. Therefore, Google’s machine learning algorithms have been trained to identify sections of neurons, including axons, bodies and dendritic trees, as well as synapses and other components. After extensive training, the millions of images that resulted from the serial electron microscopy procedure were automatically annotated by the machine learning algorithms, enabling the team to complete in just a few years the detailed neuron-level connectome of a significant section of the fly brain, which includes roughly 25000 neurons and 20 million synapses.
The results, published in the first of a number of articles, can be freely analyzed by anyone interested in the way a fly thinks. A Google account can be used to log in to the neuPrint explorer and an interactive exploration of the 3D electron microscopy images is also available with neuroglancer. Extensive non-technical coverage by the media is also widely available. See, for instance, the article in The Economist or the piece in The Verge.
Image from the HHMI Janelia Research Campus site.