WBUR’s moderator for a drowsy driving webcast that included Mark Rosekind, Arianna Huffington, Charles Czeisler, and Jay Winsten shares highlights from the discussion.

Czeisler, who’s the head of the division of sleep and circadian disorders at Brigham and Women’s Hospital, says the sleep-deprived brain can split itself in two. One part goes through the motions of a “highly over-learned task” such as driving. Meanwhile, cognitive centers involuntarily transition from wakefulness to sleep.

“So it’s particularly concerning that 56 million Americans a month admit that they drive when they haven’t gotten enough sleep and they’re exhausted,” Czeisler says. “Eight million of them lose the struggle to stay awake and actually admit to falling asleep at the wheel every month.”

My powerful mid-afternoon drowsiness was typical. “It used to be thought that [drowsiness-related crashes] only happened at night, but that’s because people weren’t looking,” Czeisler says. “Most sleep-deficient driving incidents happen during the daytime because there are so many more drivers on the road.”