Top 10 Mysteries of the Mind

Debated for centuries, the human mind still holds a mystery or two in modern times. Here are LiveScience's top 10:

1. Consciousness. Still the biggest human puzzle since Socrates.
2. Cryonics. Can gray matter be revived from a 320-degree deep freeze?
3. Aging. An unappreciated benefit, or simply cell decay with no purpose?
4. Nature/nurture. DNA, peer pressure, upbringing—scientists disagree on why we do the things we do.
5. Laughter. Three brain zones like it, but scientists wonder why people giggle at different things.

6. Memories. Scientists have spotted the brain's memory regions, but true and false memories mysteriously zap the same gray matter.
7. Biological clock. Melatonin alters it; could supplements of the hormone reduce jet lag?
8. Missing limb feelings. Nerves may relink to the spinal cord—unless the brain is permanently hardwired to think we're all there.
9. Sleeping. A time for brain hibernation, or the cataloging of memories?
10. Dreaming. Are synapses exercising as we dream, or are feelings being worked out?

(More brain stories.)