February 20, 2013
Reading Minds: System Observes Real-time Brain Activity In A Live Mouse
[ Watch the Video: Scientists Read a Mouse´s Mind ]
April Flowers for redOrbit.com - Your Universe OnlineResearchers at Stanford University have revealed a new technique for observing hundreds of neurons firing in real time in the brain of a live mouse. They have linked this activity to long-term information storage. The unprecedented work, published in a recent issue of Nature Neuroscience, could provide a useful tool for designing new therapies for neurodegenerative diseases such as Alzheimer's.
The first step was to use gene therapy to cause the mouse's neurons to express a green fluorescent protein. This protein is engineered to be sensitive to the presences of calcium ions, which naturally flood the cell when a neuron fires. The protein is stimulated by the calcium, causing the entire cell to fluoresce bright green.
The team then implanted a tiny microscope just above the hippocampus — a region of the brain that is critical for spatial and episodic memories. The microscope, connected to a camera chip, captures the light of roughly 700 neurons and transmits a digital version of the image to a computer screen.
In near real-time, the computer displays a video of the mouse's brain activity as the animal runs around a small enclosure, called an arena by the researchers.
As the neurons fire, what looks like tiny green fireworks burst in a seemingly random manner against a black background. The researchers, however, have discerned clear patterns.
"We can literally figure out where the mouse is in the arena by looking at these lights," said Mark Schnitzer, an associate professor of biology and of applied physics.
A specific neuron will fire and flash green when a mouse is scratching at the wall in a certain area of the arena. As the mouse moves to a new area, the original cell will fade to be replaced by a new spark.
"The hippocampus is very sensitive to where the animal is in its environment, and different cells respond to different parts of the arena," Schnitzer said. "Imagine walking around your office. Some of the neurons in your hippocampus light up when you're near your desk, and others fire when you're near your chair. This is how your brain makes a representative map of a space."
Even if a month passes between tests, the mouse's neurons fire in the same patterns.
"The ability to come back and observe the same cells is very important for studying progressive brain diseases," Schnitzer said.
If a particular neuron stops functioning, for example, as a result of normal neuronal death or a neurodegenerative disease, the scientists could apply an experimental therapeutic agent to the region. The mouse would then be exposed to the same stimuli to see if the neuron's function returns.
This technology cannot be tested on humans at this time, however, mouse models are common starting points for new therapies for human neurodegenerative diseases. The system could be a very useful tool in evaluating pre-clinical research.