The Grete Lundbeck European Brain Research Foundation has announced this year’s winners of The Brain Prize, a €1m neuroscience prize. It has been awarded to four scientists, Winfried Denk and Arthur Konnerth (Germany) and Karel Svoboda and David Tank (United States), for the invention and development of two-photon microscopy, a transformative tool in brain research.

Two-photon microscopy uses pulsed infrared lasers to focus the illumination only on the target area, which is the only area that then emits light. “It’s like the difference between looking at a movie in daylight and looking at a movie in a dark hall. If you take away the unwanted light, you can see what you want to see much better,” says Maiken Nedergaard, a professor at the University of Rochester Medical School, New York.

With regard to sleep research, in 2013, a combination of optical techniques shed light on the brain’s “slow waves,” rhythmic signal pulses that sweep through the brain during sleep and are assumed to play a role in processes such as the consolidation of memory. The slow waves can be observed in very early stages of development, and they may be disrupted in Alzheimer’s and other diseases. In this study, two-photon microscopy was used in conjunction with optogenetics, an approach that enabled spatially defined stimulation of small numbers of neurons. Konnerth’s group showed conclusively that slow waves start in the cerebral cortex, ruling out other long-standing hypotheses. The researchers also found that such a wave can be set in motion by a single tiny cluster of neurons. “Out of the billions of cells in the brain,” Konnerth says, “it takes not more than a local cluster of fifty to one hundred neurons in a deep layer of the cortex, called layer 5, to make a wave that extends over the entire brain.”