Scientists have studied high-frequency brain waves, known as gamma oscillations, for more than 50 years, believing them crucial to consciousness, attention, learning and memory.
Now, for the first time, MIT researchers and colleagues have found a way to induce these waves by shining laser light directly onto the brains of mice.
The work takes advantage of a newly developed technology known as optogenetics, which combines genetic engineering with light to manipulate the activity of individual nerve cells. The research helps explain how the brain produces gamma waves and provides new evidence of the role they play in regulating brain functions - insights that could someday lead to new treatments for a range of brain-related disorders.
"Gamma waves are known to be [disrupted] in people with schizophrenia and other psychiatric and neurological diseases" says Li-Huei Tsai, Picower Professor of Neuroscience and a Howard Hughes Medical Institute investigator. "This new tool will give us a great chance to probe the function of these circuits."
Tsai co-authored a paper about the work that appears in the April 26 online issue of Nature .
Gamma oscillations reflect the synchronous activity of large interconnected networks of neurons, firing together at frequencies ranging from 20 to 80 cycles per second. "These oscillations are thought to be controlled by a specific class of inhibitory cells known as fast-spiking interneurons", says Jessica Cardin, co-lead author on the study and a postdoctoral fellow at MIT's McGovern Institute for Brain Research. "But until now, a direct test of this idea was not possible."
To determine which neurons are responsible for driving the oscillations, the researchers used a protein called channelrhodopsin-2 (ChR2), which can sensitize neurons to light. "By combining several genetic tricks, we were able to express ChR2 in different classes of neurons, allowing us to manipulate their activity with precise timing via a laser and an optical fiber over the brain," explains co-lead author Marie Carlén, a postdoctoral fellow at the Picower Institute.