Seeing seeing in action

Harvard Medical School researchers are seeing what seeing does to the brains of animals and making images that show for the first time single brain cells working together.

The work, by Professor of Neurobiology Clay Reid and colleagues from Harvard Medical School, combines existing imaging techniques to create high-resolution movies of the working brain.

Previous techniques have been able to measure the firing of single brain cells, but have done so blindly. Reid said the old technology is like walking through a cocktail party with one's eyes closed and hearing conversations but never being exactly sure who's speaking. The new techniques take those blinders off, allowing researchers to even make time-lapse images of groups of nerve cells firing in response to visual stimulation.

"The new technology allows us to see it all at a glance," Reid said. "We can look at all 200 neurons [at once]."

The advance opens doors for researchers to understand the brain's functioning at a level of detail not possible before and has potential applications in the understanding of brain diseases, such as Alzheimer's.

Reid said his own work will continue on the visual cortex, a well-studied part of the brain that still holds many secrets.

"We'll see things we haven't thought of," Reid said.

Reid conducted the research together with research fellows Kenichi Ohki and Sooyoung Chung, graduate student Yeang H. Ch'ng, and instructor in neurobiology Prakash Kara. The group combined two techniques in newly powerful ways, thanks to a recent advance by German researchers.

Specifically, Reid and colleagues employed two-photon-microscopy, which uses lasers to take images from deep inside of tissues. They combined that with a dye that glows in relation to a cell's level of calcium. Since calcium levels rise when a nerve cell fires, the dye allows researchers to see active nerve cells grow brighter and then fade.