国家地理-2008-07-24 生存危机下的人体反应（在线收听）

In animals, this part of the brain evolved around the time of the dinosaurs before mammals existed. It's hardwired to beat starvation. For three days Jean-Luc has been trapped underground. He hasn't had a morsel to eat. He doesn't know it, but his brain is changing how his body functions and how he behaves.

There are a couple of different brain centers that graduate feeding behavior as well as hunger. They’re in different parts of the central part of the brain called the hypothalamus. And in that part of the brain you are really driven to seek out food to eat almost anything to try to stop yourself from starving to death.

 To drive Jean-Luc’s search for food his brain first releases a hormone--orexin. Orexin comes in tiny doses, but it has a profound effect. This hormone makes us more alert, improves our muscle efficiency, making us better hunters. It even sharpens our problem-solving skills.

 For days Jean-Luc scours the caves. He finds water but nothing to eat. He starts to fear the worst.

 Even if when I had a little hope, I thought obsessively what would happen over the last few days or the last hours before dying. It was a big question: how I would die--was it going to be cold or hunger or… It was a question that I always had in my head.

 Sure that he's doomed, he records a message. But as hope fades, Jean-Luc’s brain switches strategy to help him survive with no food. With his fuel stores depleted, his body becomes even more efficient. It makes him slow down. Now his muscles use less energy, so do all his internal organs. New cells grow more slowly. Nonessentials—fingernails, toenails, hair—hardly grow at all. Jean-Luc is entering a survival state that evolved to keep starving animals alive until they could get to food.

 This enforced efficiency which kicks in when we're at our limit may have bigger implications. Some say, it could help us all live longer.