Certain brain disorders, such as schizophrenia, autism and mental retardation are thought to be caused by a malfunction in brain cell communication and have no easy-to-detect physical signs leading to diagnosis. In fact, even fMRIs and PET scans are able to offer only limited detail of brain activity in these cases.
Now neuroscientists at the University of California, Los Angeles (UCLA) have joined forces with physicists to develop a non-invasive, extremely high speed microscope that instantly captures the firing of thousands of neurons in the brain as they communicate — or in these cases — miscommunicate with one another.
“In our view, this is the world’s fastest two-photon excitation microscope for three-dimensional imaging in vivo,” said UCLA physics professor Dr. Katsushi Arisaka, who developed the optical imaging system with Dr. Carlos Portera-Cailliau, UCLA assistant professor of neurology and neurobiology, and colleagues.
Since neuropsychiatric diseases like autism, schizophrenia and mental retardation do not usually display any physical brain damage, they are believed to be caused by conductivity problems — neurons not firing properly. Normal cells have patterns of electrical activity, said Portera-Cailliau, but irregular cell activity as a whole doesn’t create useful 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.”
Recently, Portera-Cailliau had been using calcium imaging, a method in which neurons take up fluorescent dyes. When the cells fire, they “blink like lights in a Christmas tree,” he said. “Our role now is to decipher the code that neurons use, which is buried in those blinking light patterns.”
However, says Portera-Cailliau , that technique has its limitations.
“The signal of the calcium-based fluorescent dye we used faded as we imaged deeper into the cortex. We couldn’t image all the cells,” he said.
Also, Portera-Cailliau and his team believed they were missing important information because they couldn’t capture a big enough section of the brain fast enough to measure the group-firing of individual neurons. That was the key factor that drove Arisaka and Adrian Cheng, one of his graduate students, to seek a faster method of recording neurons.
The microscope they developed is a multifocal two-photon microscopy with spatio-temporal excitation-emission multiplexing (STEM). It is a modified version of two-photon laser-scanning microscopes that record fluorescent calcium dyes inside the neurons, but with the main laser beam split into four smaller beams.
This technique lets them record four times more brain cells than the original version, four times faster. Also, a different beam was used to record neurons at various depths inside the brain, giving the image a completely novel 3-D effect.
“Most video cameras are designed to capture an image at 30 pictures per second. What we did was speed that up by 10 times to roughly 250 pictures per second,” Arisaka said. “And we are working on making it even faster.”
The result, he said, “is a high-resolution three-dimensional video of neuronal circuit activity in a living animal.”
Portera-Cailliau is already reaping the benefits of this imaging technique in his studies of Fragile X syndrome, a form of autism. Using this new technology, he is able to compare the cortex of a normal mouse with a Fragile X mutant mouse, and witness the misfiring of neurons in the Fragile X brain.
The study can be found in the Jan. 9 edition of the journal Nature Methods.
Source: University of California