March 9, 2011

Harvard Researchers Map Brain Circuitry

Tiffany Trader

The Harvard Medical School publication, Focus, has an intriguing feature article, which describes a cutting-edge neuroscience advance: brain mapping. Researchers at Harvard Medical School’s Department of Neurobiology say they’ve figured out a technique for crawling through the connections in the brain much like the way a computer algorithm crawls through network connections, like those in popular online apps, such as Google and Facebook. This is no easy task. Compared to computer circuits, with their fairly straightforward design, the brain’s neural system is a tangled mess. But if that mess could be unraveled, the applications are “too numerous to list,” according to Clay Reid, HMS professor of neurobiology and senior author on a paper in the March 10 edition of Nature, which details the findings.

Reid’s lab has been studying the cerebral cortex for some years, and they have had some success in isolating the activities of individual neurons. For example, they are able to observe them fire in response to external stimuli. But they have not yet been able to get inside a single cortical circuit and “probe the architecture of its wiring.” The article explains that just one of these circuits contains between 10,000 and 100,000 neurons, and each neuron makes about 10,000 interconnections. Which means a single circuit can contain more than one billion connections.

Determined to figure out not only what the circuit does, but how it does it, Reid’s team employed a two part approach. First, they developed an imaging technique, which they used to detail the vision processing center of a mouse brain. Advanced microsopy tools enabled them to view the neurons at nanometer-level resolution. After they’d recorded more than 3 million such high-resolution images, the data was sent to the Pittsburgh Supercomputing Center at Carnegie Mellon University, where it was reconstructed into 3D images. The second stage of the project was even more challenging: unravelling the mass of neurons. For this, the team selected 10 individual neurons for mapping. By carefully tracing each neuron, they were able create a partial wiring diagram.

A related video shows the wiring diagram. It also includes side-by-side videos: on the left is the movie shown to the mouse; on the right is the recording of the visual neurons. While not a perfect match, the similarity is evident. The next step for the researchers is to scale up the system to handle larger data sets.

Possible future applications sound like the stuff of science fiction. Reid believes that in as little as ten years, it could be possible to use the imaging technique to record the activity of thousands of neurons in a living brain, stating: “In a visual circuit, we’ll interpret the data to reconstruct what an animal actually sees. By that time, with the anatomical imaging, we’ll also know how it’s all wired together.”

Full story at Focus (a publication of Harvard Medical School)

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