Behind the controls of the Metro-North train that derailed in New York earlier this week was a tired driver, according to new reports that engineer William Rockefeller fell asleep at the wheel.
Could lack of sleep cause such a fatal mistake?
Biologically speaking, experts said, yes. Sleep deprivation affects the brain in multiple ways that can impair judgment, slow reaction times and increase the likelihood of drifting off during monotonous tasks.
"When you're sleep deprived, your brain reverts to a teenager -- it's all gas and no brake," said Michael Howell, a neurologist at the University of Minnesota, Twin Cities. "Suddenly the part of the brain that says, 'Let's think through this,' is not functioning well."
The purpose of sleep has long mystified scientists, said Maiken Nedergaard, a neuroscientist at the University of Rochester Medical Center in New York. In an evolutionary conundrum, lying unconscious for hours on end makes people and other animals vulnerable to predators. Yet, not sleeping for long enough can actually lead to dementia and death. Chronic sleep-deprivation can cause obesity, diabetes, heart disease and other ills.
Studies have shown that exhausted people do worse on tests of memory and have more trouble learning. Tired basketball players sink fewer free throws. Even golfers who fail to get enough shut-eye take more strokes to finish a round.
"Almost everything researchers have looked at," Howell said, "they've demonstrated is impaired if you don't get enough sleep."
When it comes to accidents, sleep matters because failure to get enough rest hampers functioning of the brain's frontal lobes, which are responsible for executive judgment, or the ability to pay attention and make good decisions.
In overtired people, Howell said, imaging studies have shown that there is less blood flow to these areas in the front of the brain and brainwaves there move more slowly.