The brain is a black box. A complex circuitry of neurons fires information through channels, much like the inner workings of a computer chip. But while computer processors are regimented with the deft economy of an assembly line, neural circuits are impenetrable masses. Think tumbleweed.
In the March 10 issue of Nature, Clay Reid, an HMS professor of neurobiology, reports a technique that unravels these masses and allows researchers to “crawl” through the individual connections of a neural network.
The cerebral cortex, arguably the most important part of the mammalian brain, helps us to perceive, remember, and plan. The ultimate prize for researchers would be to probe the architecture of a single cortical circuit—which contains between 10,000 and 100,000 neurons, each of which makes about 10,000 interconnections.
Reid’s team embarked on a two-part study of the pinpoint-sized region of a mouse brain that is involved in processing vision. They injected the brain with dyes and recorded the flashes as specific neurons fired. The team then used electron microscopy to take nanometer-resolution images of the same neurons, which they used to trace the connections of ten individual neurons.
The team found that neurons that inhibit brain activity seem to be randomly wired, shutting down groups of neurons rather than individual ones. Such findings are important; epilepsy and other neurological conditions result from neural inhibition gone awry.
“This is just the iceberg’s tip,” says Reid. “Within ten years I’m convinced we’ll be imaging the activity of thousands of neurons in a living brain.”
Image: Kris Snibbe/Harvard News Office