To understand the root of the problem of these latter diseases, visualizing brain activity is the key. But even the best imaging devices available — fMRIs and PET scans — can only give a "coarse" picture of brain activity.

Neuroscientists have now collaborated with physicists to develop a non-invasive, ultra–high-speed microscope that can record in real time the firing of thousands of individual neurons in the brain as they communicate, or miscommunicate, with each other.

"In our view, this is the world's fastest two-photon excitation microscope for three-dimensional imaging in vivo," said Professor Katsushi Arisaka, who designed the new optical imaging system with UCLA assistant professor of neurology and neurobiology Doctor Carlos Portera-Cailliau and colleagues.

Because neuropsychiatric diseases like autism and mental retardation often display no physical brain damage, it's thought they are caused by conductivity problems — neurons not firing properly. Normal cells have patterns of electrical activity, said Portera-Cailliau, but abnormal cell activity, as a whole does not generate relevant information the brain can use.

"One of the greatest challenges for neuroscience in the 21st century is to understand how the billions of neurons that form the brain communicate with one another to produce complex behaviors," he said. "The ultimate benefit from this type of research will come from deciphering how dysfunctional patterns of activity among neurons lead to devastating symptoms in a variety of neuropsychiatric disorders."

The imaging technology they developed is called multifocal two-photon microscopy with spatio-temporal excitation-emission multiplexing — STEM for short. The researchers modified two-photon laser-scanning microscopes to image fluorescent calcium dyes inside the neurons, and came up with a way to split the main laser beam into four smaller beamlets. This allowed them to record four times as many brain cells as the earlier version, or four times faster. In addition, they used a different beam to record neurons at different depths inside the brain, giving a 3-D effect, which had never been done previously.

The use of calcium imaging in research is already providing dividends. Portera-Cailliau studies Fragile X syndrome, a form of autism. By comparing the cortex of a normal mouse with a Fragile X mutant mouse, his group has discerned the misfiring that occurs in the Fragile X brain.; Source: University of California - Los Angeles