Quiz: How Well Do You Know Your Brain?

Your brain doesn't really do several tasks at once when you multi-task. It switches very quickly from one task to another. Because switching takes time, multi-tasking isn't a very effective or efficient way to work.

Scientists are still puzzled about why people have déjà vu -- the feeling that you've been somewhere or done something before even when you haven't. But new research suggests that déjà vu occurs when people are somewhere new that's similar to a place they've been or do something similar to something they did before. For a moment, they mistakenly think they were there or did it in the past. 

A bigger brain doesn't always mean bigger thoughts. In fact, human brains were larger back when we were living in caves, but our bodies were also larger then. As we evolved, more of the space in our brains became used for complex processes such as language, thinking, and memory. 

A 1999 study of Einstein’s brain, based on photographs taken of it after he died in 1955, showed that the parietal lobes, which are linked to math ability, appear 15% wider than normal. But the size of his brain was a little smaller than average.

We may be the smartest creatures on the planet, but others have bigger brains. Larger brains are needed partly to control larger muscles. A sperm whale's brain weighs about 17 pounds and an elephant's weighs a little more than 10 pounds. An owl's brain weighs 0.005 pounds and a bullfrog's about one-tenth of that.

When researchers looked at brain scans of Buddhist monks meditating, they found that the parts of the brain that help people concentrate and make decisions became more active. The burst of activity was very strong in young monks learning to meditate. But it was smaller in monks who had meditated more. This could mean the older monks' brains had learned to focus more easily.

The right side of your brain controls movements on the left side of your body whether you're right or left handed. The left side of your brain controls movements on the right side. That's why damage on one side of your brain affects the other side of your body. So if you have a stroke in the left part of your brain, your right arm or leg could be paralyzed.

The two sides of your brain, called hemispheres, look almost identical. But they handle different tasks. When you form words or do math, you use mostly the left side. Face recognition, spatial abilities, and music are tied to the right side.

To keep your brain fit, you need to exercise it. Learning new skills or doing mental tasks makes the connections between brain cells stronger. Staying curious can help it stay sharp as you age. Exercise also appears to help us keep brain power.

A stroke happens when a blood vessel in your brain breaks or gets blocked. High blood pressure -- along with diabetes and smoking  -- can damage blood vessels including those that supply your brain, raising the risk for a stroke.

Brain cells, or neurons, are separated by tiny gaps, called synapses. When a signal reaches the end of a nerve fiber, it releases neurotransmitters, which cross the gap to the receiving neuron. Movements, thoughts, memories, sensations, and feelings are all due to signals passed by neurons.

Gray matter includes neuron cell bodies in the thin outer layer of the brain. White matter appears white because it mainly contains nerve fibers coated with a sheath called myelin.  The sheath allows neurons to send messages, or nerve impulses, faster.

Your brain is only about 2% of your body weight, but brain cells use twice as much energy as other cells in your body. Brain cells are always active, even when you sleep.

Studies suggest that your brain is aware of subliminal, or hidden, messages even when you aren't. Human faces that express emotions, such as smiling or frowning, seem to have the strongest impact. Words are weaker at conveying hidden messages.

The average adult human brain has about 100 billion cells. Linked by synapses, each brain cell can connect to tens of thousands of other brain cells. It's still a mystery exactly how these connections work together to create all the marvels of our brains.

Researchers think that sleep gives the brain time to process and store memories. We seem to save memories of how to do things such as play piano or ride a bike during sleep. People who don’t get enough sleep have trouble concentrating and recalling memories.

Brain cells are the longest living cells in the body. Research shows that some parts of the brain may be able to grow new neurons as we age. But most of our brain cells are present from birth to death. The wiring of these cells changes constantly through our lives.