Snakes on the brain

Researchers now can say what would happen in Samuel L. Jackson’s brain if he really were to confront snakes on a plane. In a terrifying sequel to that movie scenario, researchers convinced volunteers to bring a slithery serpent within centimeters of their heads while they lay trapped in a brain scanner.

The experiment, published June 24 in Neuron, allowed researchers to watch brain activity as people chose to quell their fear and bring the snake closer to their heads, offering a glimpse into the courageous brain. Understanding how the brain chooses to overcome fearful impulses may help scientists treat people with phobias, panic disorders or PTSD. 

“This is a breakthrough study that will set the stage for a whole new area of work related to the brain and fear,” says neuroscientist Joseph LeDoux of New York University, who was not involved in the research.

Scientists have figured out much of what happens in the brain during fear, LeDoux says, but almost nothing is known about the ability to overcome the reaction.

To see what happens in the courageous brain, researchers led by Yadin Dudai of the Weizmann Institute of Science in Israel enlisted brave volunteers who admitted to being afraid of snakes but still agreed to try to overcome their fear in a laboratory experiment.

Dudai and his colleagues designed a conveyer belt that carried a large, writhing snake strapped to the top of a box with a single piece of Velcro. Sixteen volunteers were confined inside an fMRI scanner with the snake behind their heads and were repeatedly given the choice to push a button that brought the snake 11 centimeters closer, or moved it 11 centimeters away. After each choice, a mirror showed the person the snake’s location.

The meter-and-a-half-long corn snake in the experiment is “actually quite a benevolent snake,” says Dudai. “It’s not a poisonous snake, but for people who fear snakes, it’s enough.”

As the subjects chose to advance the snake, a move interpreted as courageous, Dudai and his team scanned their brain activity. The team then compared which brain regions were active to the parts that lit up when a subject succumbed to fear and moved the snake away. This comparison turned up a region in the front of the brain called the subgenual anterior cingulate cortex, or sgACC, that was active when courage was on display, but quiet when fear took over. This brain region may have many functions, including regulating fear, studies suggest.

Surprisingly, when the sgACC revved up, the researchers noticed that bodily indicators of fear, such as increased sweating, were reduced. Dudai and his team hypothesize that this brain region is crucial for directing the body to ignore fear. Stimulating or activating this region might one day help people with phobias to overcome their fears. 

The new study is “certainly beginning to touch on understanding courage, but it might not necessarily explain all aspects of courage,” comments neuroscientist Mohammed Milad of Harvard Medical School, who studies how the brain gets rid of fear. Milad points out that the lab experiment lacks the altruistic components sometimes found in courage, for example the drive to run into a burning building to save a child.

But Milad adds that this study is the closest researchers have come to studying real courage in the lab. “The design is so clever, and daring, and novel, in many respects,” he says. “To be able to take a live snake, tie it to Velcro and put it in a room is just insane. It’s really amazing that they were able to do that.”