Wang and the team then used the microscope to track changes in the visual cortex of mice in response to different visual stimuli. The researchers could detect when Arc was turned on in the visual cortex over the course of several days, and they could also get clues about Arc’s function by looking for differences between the mice that still expressed Arc and those that didn’t.
The researchers found that Arc changes the way neurons respond to the visual world. For example, when mice that expressed Arc were repeatedly exposed to either horizontal or vertical lines, their visual systems were more “in tune” to that stimulus, responding more specifically to the stimuli they had been exposed to.
Wang believes that because Arc is active throughout the brain, it can be used as a general marker of activity in brain cells. These engineered mice, he says, can be used “to locate cells in a variety of regions that are activated by normal sensory experience.”
The technique could also be used to monitor cell activity in animal models of neurological disease or degeneration, or to test the effects of therapies in treating these conditions.
Josh Huang, a neuroscientist at Cold Spring Harbor Laboratory in New York, says that this study is an innovative way to study plasticity, the ability of neurons and their connections to change in response to experience. “It’s very clever and certainly shows in the fluorescent neurons that some cellular plasticity event is going on,” he says. But he says that Arc would be more useful if more were known about how it is activated; otherwise it’s difficult to know exactly what its activity represents.
Huang says his lab is developing ways to study brain circuitry through other genes or cellular processes regulated by activity or experience. He adds that scientists would like to find ways to visualize the brain’s activity on several different levels, from the instantaneous firing of a neuron to the long-term changes that help the brain form memories.