Your brain has billions of neurons (brain cells) and trillions of connections between those neurons.  Brain cells are not physically connected directly with each other like the wires in your house or car.  The neurons are connected indirectly through special chemicals called neurotransmitters.

When one brain cell talks to another, it sends the message using neurotransmitters.  The sending cell releases a tiny packet of chemicals that carries the message to the receiving cell.  This scenario repeats itself trillions of times each day.  The amount and distribution of the neurotransmitters is critical to the normal functioning of your brain.

The health of your brain cells and the amount of neurotransmitter chemicals available have a great deal to do with your state of mind.  People who have severe depression are often found to have a deficiency in the amount of neurotransmitters available for use.  Drugs that deplete the supply of neurotransmitters often lead to depression.  Drugs that elevate the supply tend to alleviate depression.

For thousands of years, people have experimented with the chemistry of their brain.  Alcohol, LSD, peyote, hallucinogenic mushrooms, ecstasy, amphetamines, crack cocaine, heroine, and marijuana are all chemicals that people use to change their brain chemistry to achieve a different mental state.  These chemicals alter the physiology of your brain, and if you abuse them long enough, they alter the anatomy as well.

Changing the physiology of your brain takes your mind on a temporary trip to another location.  Changing the anatomy not only takes you to a different mental destination, it leaves you there with permanent brain damage.

While it is obvious to most people that you can alter your brain chemistry using chemicals, it's much less obvious that you can alter it by changing what you put into your mind.  Although further research needs to be done in this area, one thing is clear.  Whatever your state of mind, there is a brain chemistry that corresponds to it.

Excerpt from :

Zero Tolerance To Negative Thinking : Good-by Depression - Hello Positive Mind

David J Abbott M.D.