Entries in circuitry (1)

Monday
Apr072014

Street view for the Brain: mapping the connectome

The race to understand the human brain is vaguely reminiscent of that to map the human genome 10 years ago. Since last year’s presidential announcement of the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, there seems to be an omnipresent interest in understanding the complexities of the mind. Similar to the human genome project, there is a major effort to demystify the brain by creating a map of the underlying connections and circuitry—the connectome. A clear reference picture of how things look and work when they are functioning properly in a healthy human brain affords the ability to identify differences that arise with damage and disease. Although this may sound like a straightforward task, you must consider the number of variables involved: mapping 80+ billion neurons, 10,000+ neural connections, throughout each stage of development, learning and aging - it is an image of a dynamic process. Here at the Martinos center, scientists are hammering away at the human connectome using various MR-based imaging tools like diffusion tractography, which traces axonal fiber bundles throughout the brain indicating the path connecting functionally-related regions.

Animal models offer the advantage of manipulability and permit much more invasive techniques, which scientists are using to create a “mesoscale” connectome map. Researchers at USC (www.mouseconnectome.org) and the Allen Brain Institute (www.brain-map.org) are creating atlases of individual axonal projections by injecting anterograde/retrograde tracers and fluorescent protein producing virus, respectively, directly into specific brain regions. By following the path of the tracer or the virus, they can define the network of potential connections each neuron can make within the brain. Both of these projects take a systematic approach, breaking the brain down into a navigable, albeit massive, data sets. The best part being that these data are publically available online for use by other scientists- or for anyone to peruse! Both of these studies were recently published and will surely serve as an invaluable resource during continued efforts to understand the brain and learn to repair damages to it.

MAPPING THE MOUSE CONNECTOME

a, The data generation and processing pipeline. QC, quality control. b, The two main steps of informatics data processing: registration of each image series to a 3D template (upper panels) and segmentation of fluorescent signal from background (lower panels). c, Distribution of injection sites across the brain. The volume of the injection was calculated and represented as a sphere. Locations of all these injection spheres are superimposed together (left panel). Mean injection volumes ( ± s.e.m.) across major brain subdivisions are shown (Image from Oh et al, 2014)

References

SW Oh et al. “A mesoscale connectome of the mouse brain,” Nature, 000, 1-8, 2014. 

www.brain-map.org

 

B. Zingg et al., “Neural networks of the mouse neocortex,” Cell, 156:1096–1111, 2014.

www.mouseconnectome.org