As wise as the counsel to "finish what you've started" may be, it is also sometimes critically important to do just the opposite -- stop.
And the ability to stop quickly, to either keep from gunning the gas when a pedestrian steps into your path or to bite your tongue mid-sentence when the subject of gossip suddenly comes into view, may depend on a few "cables" in the brain.
Researchers led by cognitive neuroscientist Adam Aron, an assistant professor of psychology at the University of California, San Diego, have found white matter tracts -- bundles of neurons, or "cables," forming direct, high-speed connections, between distant regions of the brain -- that appear to play a significant role in the rapid control of behavior.
Published in the April 4 issue of the Journal of Neuroscience, the study is the first to identify these white matter tracts in humans, confirming similar findings in monkeys, and the first to relate them to the brain's activity while people voluntarily control their movements.
"Our results provide important information about the correspondence between the anatomy and the activity of control circuits in the brain," Aron said. "We've known for some time about key brain areas involved in controlling behavior and now we're learning how they're connected and how it is that the information can get from one place to the other really fast."
"The findings could be useful not only for understanding movement control," Aron said, "but also 'self-control' and how control functions are affected in a range of neuropsychiatric conditions such as addiction, Tourette's syndrome, stuttering and Attention Deficit Hyperactivity Disorder."
To reveal the network, Aron and researchers from UCLA, Oxford University and the University of Arizona performed two types of neuroimaging scan on healthy volunteers.
They used diffusion-weighted MRI, in 10 subjects, to demonstrate the "cables" between distant regions of the brain known to be important for control, and they used functional MRI, in 15 other subjects, to show that these same regions were activated when participants stopped their responses on a simple computerized "go-stop" task.
One of the connected regions was the subthalamic nucleus, within the deep-seated midbrain, which is an interface with the motor system and can be considered a "stop button" or the brake itself. A second region was in the right inferior frontal cortex, a region near the temple, where the control signal to put on the brakes probably comes from.
"This begs the profound question," Aron said, "of where and how the decision to execute control arises."