The brain’s functional network is both highly complex and hard to peer into, making it difficult to understand how some neurons are related to others and what their interconnectivity is like. Researchers at the Max Planck Institute of Neurobiology in Martinsried, Germany have now developed a way to visualize the electrical activity that single neurons generate and how they affect other cells in the vicinity.
Relying on optogenetics, a technology developed in the last few years that permits light to be used to stimulate genetically reprogrammed brain cells, the team was able to engage individual neurons and then see which nearby neurons react. Moreover, the shape and the contacts of the neurons can also be seen.
Previously, finding a single electric pathway was an extremely tedious and somewhat expensive process, involving tiny electrophysiology needles and an electron microscope. And while the pathway was identified, the way that electricity actually makes its way through a pathway was unseen.
The recent work was performed on brains of zebrafish larva, as they’re transparent and easy to work with. Nevertheless, the findings that this technology will make possible should have a profound effect on our understanding of the human brain.
Some more detail about the research from Max-Planck Gesellschaft:
With the help of genetic technology methods, the researchers infiltrated the light-sensitive ChrimsonR ion channel into individual neurons in the brain of zebrafish larvae. They also caused the neurons in the surroundings of these ChrimsonR cells to produce GCaMP6, a calcium indicator. A bright fluorescent protein, with which the researchers could make the shape of the neurons, their intricate ramifications and synapses visible, was coupled in turn to GCaMP6.
Because zebrafish larvae and their brains are transparent, the Max Planck researchers were able to activate the ChrimsonR cells simply by focusing light on the fish.
This meant that the researchers were able to activate individual ChrimsonR cells in the living fish brain using light. When the ChrimsonR cell triggered an action potential in a neighboring cell, the calcium indicator there reacted to the associated ion influx and the fluorescent protein caused the cell to light up and thus stand out of the crowd through its change in brightness. This enabled the scientists to observe, live under the microscope, which neuron types were activated following the activation of the initial cell, and when and where they became active.
Image: Researchers can activate individual neurons in the zebrafish brain with light (magenta) and observe which neighboring cells are connected to the neuron in the same circuit (yellow). © MPI of Neurobiology/ Förster