The human brain is an incredible organ. Weighing a mere three pounds, it is the home of our entire essence: Our thoughts, fears, likes and dislikes, goals and dreams. The brain’s 100 billion neurons and quadrillion synapses are responsible for our ability to think, write, run, breathe, and laugh. We often take these abilities for granted, forgetting the complex cognitive processes that enable them to occur.

Take laughing, for example. Research shows that laughing involves activity in five different parts of the brain: the frontal lobe, the right and left hemispheres of the cortex, the occipital lobe, and the motor cortex.

Here are ten other surprising facts about the brain:

1. The average person has about 60,000 thoughts each day.

Of these thoughts, 70 percent are negative. So if you tend to see the glass half-empty, you’re not alone.

2. The brain is 73 percent water.

Even the slightest amount of dehydration can temporarily shrink the amount of grey matter in the brain, thereby affecting memory and attention, among other cognitive capacities. In fact, 90 minutes of sweating can shrink the brain the equivalent of one year of aging! (Have no fear – the brain returns to normal size and function with adequate fluids.)

3. Learning a new skill can change your brain in just one week.

A study in Germany found that learning a new skill, like juggling, creates visible changes in the brain after only seven days. After one week of practice, novice jugglers had increased activity in the V5 area of the occipital lobe, a region that is sensitive to motion. The researchers attributed the findings to neuroplasticity, the brain’s ability to form new neural connections throughout life.

4. The average attention span today is about eight seconds, which is one second shorter than that of a goldfish.

Yes, this is slightly alarming.

5. The first brain surgery was performed in 2000 B.C.

In prehistoric times, trepanation, a procedure that involved drilling a hole in the skull, was commonly performed for spiritual reasons or to treat headaches or mental illness. Hundreds of trepanized skulls from pre-Incan civilization were discovered by archeologists in South America. The skulls showed evidence of healing, which suggests that the patients likely survived the procedure.

6. Multitasking is impossible.

Most of us think that we can simultaneously listen in class while checking Facebook or Twitter. But when we think we are multitasking, we are actually engaging in context-switching, which means going back and forth between tasks. Context-switching is associated with double the amount of time to complete tasks as well as twice as many errors in the process. This is because multitasking involves dividing up precious brain resources among the multiple tasks in addition to the actual process of constantly switching our attention. Studies show that when people are given two or three tasks to complete, their performance suffers significantly.

7. The average person has about four to seven dreams every night.

We typically don’t remember our dreams because they are usually forgotten within 90 seconds of waking up.

8. Your taxi driver has a larger hippocampus than you.

A 2006 study conducted in London found that taxi drivers had more gray matter in their hippocampal region of their brains compared to bus drivers who follow routes. The hippocampus is associated with memory and navigation. The lead author of the study, Dr. Eleanor Maguire, says, "There seems to be a definite relationship between the navigating they do as a taxi driver and the brain changes-- The hippocampus has changed its structure to accommodate their huge amount of navigating experience." In other words, having to figure out directions and calculate the best routes to get around traffic contribute to brain development.

9. Your brain needs stimulation.

Studies show that people would rather receive electric shocks than sit quietly in a room and think.

10. There is no such thing as being “right-brained” or “left-brained.”

We use both hemispheres to perform daily tasks. Certain abilities like handedness and speech are located in one hemisphere more than the other, but all tasks require communication between both hemispheres. This communication is made possible via the corpus collosum, the fiber connections between the left and right hemisphere.