The great American poet Ralph Waldo Emerson once said, “Finish each day before you begin the next, and interpose a solid wall of sleep between the two.”

That endorsement for sound sleep was written in the nineteenth century, but no matter the era, a solid night’s slumber has always been the stuff of lullabies.

But why do people become frazzled when they don’t have a wall of sleep to protect them?

Scientists with the University of California Berkeley and Harvard University set out to find the answer.

In an experiment using functional magnetic resonance imaging, twenty-six young adult volunteers were kept awake for a day, a night and another full day. Twenty-six others slept normally.

Scans showed that shutting down the shut-eye short-circuited thought.

The brain’s fear center… the amygdala [Ah-MIG-dah-la]… kicked into gear, while the calm, rational prefrontal cortex appeared to fall asleep on the job.

In effect, the sleep-deprived brains fell into a primitive “fight or flight” state.

Not only did the scans show the subjects’ emotional centers surging, lab workers noticed the sleep-deprived volunteers behaved erratically, upset at one moment, giddy the next.

Apparently, even healthy brains seem to develop psychiatric symptoms when lacking sleep.

That interplay between sleep and psyche [sike-ee] underscores the value of the seven to nine hours of sleep that most adults should get each night.

But we like the way the great English poets Lennon and McCartney said it:

“When golden slumbers fill your eyes, smiles awake you when you rise.”