Did you know you have around 100 trillion nerve cells in your brain? Each one is capable of growing up to 70,000 branches called dendrites. Scientists have been able to understand more about the nature and function of dendrites with advances in imaging technology, electrophysiology and molecular approaches. They have discovered that the brain builds a double memory of the content of every thought, one on the left side of the brain and one on the right.
The left brain's perspective on information processes it detail to big picture, while the right side processes it big picture to detail. Both sides of the brain take part in every activity, just from different perspectives. Referring to left-brain function as academic, and the right-brain function as creative no longer makes sense.

In the physical, biochemical and neurological process involved in the formation of thought there is a certain point when you can control the thought and decide whether to accept or reject it. Once the thought is beyond this cut-off point, it is no longer controllable and if negative, has the potential to become a constant internal stressor with all the negative implications for your health in body and mind.

Reference: “Who Switched off my Brain” by Dr. Carolyn Leaf.
http://drleaf.com/thought_life.php