In what some have labeled as mass hysteria, nearly 150 pilgrims to a mountain temple in India perished Sunday in a stampede that local officials say was triggered by rumors of a landslide.
There was no landslide, but one expert was quick to caution that the incident should not simply be written off as an instance of mass hysteria.
"What would be one person's hysteria is another person's genuine belief," said Anthony Mawson, an epidemiologist at the University of Mississippi Medical Center in Jackson, and the author of "Mass Panic and Social Attachment."
"I don't necessarily think there's a difference between false beliefs and true beliefs in the way people behave," he said. "Any belief, true or false, which causes people to move in threatening directions, causes adverse consequences."
Mawson explained that, while a few people may have panicked by the fear of a landslide, most responded to the genuine concern of being stampeded.
Mawson and other experts say there is a complex mind-set that occurs in people during disasters, which may explain why mass panics are the exception, rather than the rule.
But what allows fears -- true or false -- to spread so quickly in crowds?
"One of the concepts underlying mass hysteria is the idea that emotions can be contagious," said Dr. Srini Pillay, an assistant professor of psychiatry at Harvard Medical School and McLean Hospital, and the former director of the panic disorders program there.
"Brain imaging studies have shown that the emotions that we experience from other people can actually have a direct impact on our brains," he said.
The region of the brain known as the amygdala is particularly instrumental in fear responses, Pillay said.
"For example, if you show a person a fearful face ... the fearful face itself will activate the amygdala in your own brain, thereby setting off the fear circuits in your brain," he said. "So, you can imagine in a crowd, all it takes is for a few people to have fearful faces to set off the fear circuits in the brains of other people."
Pillay explained that people have two circuits for fear. The quicker one comes from the amygdala, which causes a small amount of panic, when, say, you step near a suspicious-looking coil on the ground. The second, from the cortex, is more rational, and will halt your panic when you realize the coil is just rope, and not a snake.
In a situation when a person is surrounded by a panicked crowd, Pillay said, the cortex does not have the chance to stop the amygdala's panic, because the brain is getting fearful input from those other people.
But both Mawson and Pillay were quick to point out that the fight-or-flight response, to which most attribute these panics, is not the primary reaction. For most people, the first thought is about their loved ones who might be nearby, they said.
"I think people often think about fight or flight being the typical response to danger," Mawson said. "Affiliation ... is a much stronger motivating factor."
Pillay agreed. "Contrary to what it often looks like ... people are usually trying to take care of each other or looking for loved ones in those contexts," he said.
He added that, in human psychology, social attachment has a very high position in the hierarchy of priorities.
"Because it has a strong position, it takes precedence over the need to protect oneself only," Pillay said.