Light Tomography of the Brain

Hans-Ulrich Dodt of the Vienna University of Technology (formerly of the Max Planck Institute) has devised a way of creating a 3-D tomographic image of the brain using light and fluorescence.

Using rodents genetically engineered to produce florescent molecules in their nerve cells, the team extracted whole mouse brains and submerged them in alcohol to flush the water out of the tissues. The dehydrated brains were then placed into an oil mixture containing the solvents benzyl-benzoate and benzyl-alcohol.

Importantly, this medium has exactly the same light refractive index as protein – meaning that any light passing through the medium would continue to pass through the brain tissue at the same angle. Usually, when light enters a body tissue, it is scattered by the different refractive index of the tissue, in the same way that light is bent as it passes through water, making submerged items appear distorted.

The medium effectively made the organ transparent, much like a drop of oil on a piece of paper can make light pass more easily through the page, Dodt explains.

....The next step involved viewing cross-sections of the brain by shining a thin sheet of light through the organ. As this sliver of light about six micrometres thick passed through the brain, it caused all of the neurons in its path to fluoresce. A computer then integrated the images obtained from scanning the thin sheet of light across the brain to give a 3D picture of how the nerves connect (see the results pictured, lower right)

Dodt claims the technique is a significant advance over previous methods to image the brain. Typically, approaches have involved physically cutting the brain into thin slices, and then staining the neurons in each slice. But the act of physically slicing the organ can distort the position of the nerves, he explains.

By comparing the scans of mouse embryos with those of adult mice they hope to get a better view on how mammalian brain networks change during development. This could give new insight into how mammalian brains change over time and what happens to information networks as a result of disease.

Source

Hat tip Kurzweilai.net

Combining such techniques with new superlens technology, should provide information about the 3-D structure of the intact brain far beyond any other tomographic technology until now.