Issue link: http://cp.revolio.com/i/5039
55 www.hplusmagazine.com The ATLUM2 machine Today only tiny volumes of neuropil (the Free Dictionary: "the complex network of unmyelinated axones, dendrites, and glial branches that form the bulk of the central nervous system's grey matter and in which nerve cell bodies are embedded") can be traced at electron microscopy resolution using painstaking manual techniques. Mapping the neuronal network of the nematode worm C. Elegans was a decade- long Herculean task, even though it is less than 0.01mm 3 in volume. Hayworth wants to use his device to cut an entire mouse brain into such thin slices that an electron microscope can scan virtually all of the structures within the tissue. As small as a mouse brain is, at 30 nm thickness, that would require approximately 2 million slices! To accomplish this, the mouse brain would be chemically fixed and embedded in plastic. Then, using a special slicing device which Ken is also designing, the plasticized brain would be cut into approximately 400 sub-blocks. Each sub-block would then be loaded into Ken's ATluM2 and it would be cut into 5,000 incredibly thin slices. Each slice would be picked up on a long carbon- coated tape for later staining and imaging in a scanning electron microscope (SEM). Because the process is fully automated, volumes as large as tens of cubic millimeters (large enough to span entire multi-region neuronal circuits) can be quickly and reliably reduced to a tape of ultrathin sections. Ken's original ATluM machine has already collected over 1,000 sections of embedded mouse cortex, each 30nm thick and 1mm x 5mm in area. SEM images of these ATluM-collected sections can attain lateral resolutions of 5nm or better, which is sufficient to image individual synaptic vesicles and to identify and trace all circuit connectivity. Following collection, the ATluM tape can be stained with heavy metals (or other markers), and cut into shorter lengths. This allows rows of sections to be attached to large (200mm diameter) imaging plates that can be loaded into a standard SEM for automated random access imaging of any location within any of the hundreds of sections on the plate's surface. A few dozen of these plates could hold an entire 10mm 3 volume representing an incredible 1x10 16 voxels of raw image data. Bulk imaging of such a large volume at the highest resolution would take hundreds of years, but having the ultrathin sections laid bare on a set of tissue plates solves this problem. luckily, a researcher can quickly produce a lower-resolution image set of the entire volume, setting up a unified coordinate system for the sample volume and plates, and then use robotic loading and positioning of plates to zoom in on any part to obtain the highest resolution SEM images. In the near future, multi-beam scanning electron microscopes will shorten the time it takes to scan such samples in high resolution, and efforts similar to the Human Genome Project, whereby hundreds of sequencing machines were used at once, might allow researchers to use hundreds or thousands of electron microscopes simultaneously to map entire brains within days rather than years. Once Ken's ATluM2 is perfected, it will hopefully go into production and copies of the device will find their way into neuroscience labs around the world. At first, these devices will be used to section areas of the brain that are of particular interest to the individual researchers. The circuitry could be used to emulate those brain functions, run experiments emulating a brain section, and possibly even test pharmaceuticals or therapies. In the future, we might understand brain circuitry so well that such devices could be used to scan and "upload" an individual's mind to any type of substrate (a new body, robot, or artificial environment). This Matrix-like immortality would be the ultimate backup of ourselves. Ken Hayworth http://geon.usc.edu/~ken/ Ralph Merkle on "large Scale Analysis of Neural Structures" http://www.merkle.com/merkleDir/brainAnalysis.html resources