How Negative Thoughts Affect Brain Health + What To Do About Them

Here's something to ponder. Every time you have a thought—and it's estimated that about 60,000 of them ricochet through your mind each day—your brain pumps out chemicals that influence the way you feel. And it happens almost instantly.

Whenever you have a sad thought, an unkind thought, or a hopeless thought—such as "I'm never going to land my dream job"—your brain pumps out a dose of chemicals that make you feel bad. On the flip side, conjure a happy, loving, or encouraging thought, and your brain gives you a blissful jolt of feel-good chemicals.

It seems obvious that if you want to feel better, you should consciously fill your head with hopeful thoughts. But most of us have no control over our thoughts. They pop in automatically, and they're overwhelmingly negative. These automatic negative thoughts (ANTs) infest the brain and steal your happiness.

Think of these ANTs as you would the ants that might bother you if you were on a romantic picnic. One ANT, like one pesky critter at your picnic, is no big problem. Two or three ANTs, like two or three insects at your picnic, become a bit more irritating. But having hundreds of ANTs, like hundreds of creepy-crawlers at your picnic, can ruin your day. 

Several years ago, I did a brain imaging study comparing the effects of both ANTs and gratitude on brain function. For this study, we performed two brain scans on the same woman—one while she was contemplating everything she was grateful for in her life and another while her head was filled with negativity—ANTs.

The first scan revealed that gratitude and healthy thinking enhanced brain function. The regions of her brain associated with mood looked calm with optimal activity.

For the second scan, we asked her to focus on sad, frightening, worrisome ANTs. She imagined her beloved dog getting sick and dying. She worried about losing her job and running out of money. And she envisioned becoming homeless. Scary stuff.

Her second scan showed that her brain on negativity looked vastly different from that healthy scan. In particular, two important brain regions showed a serious and concerning decrease in activity.

First, it looked like her cerebellum, usually one of the most active areas of the brain, had gone on strike. Located at the back of the brain, the cerebellum is involved in motor coordination and thought organization and is essential for processing complex information. When this region is underactive, people tend to be clumsier—both in their physical movement and in their cognitive processes.

The link between our thoughts and brain activity has been noted for decades. As early as 1995, researchers at the National Institute of Mental Health were using neuroimaging to investigate how thoughts affect brain function1. They put healthy women in a functional brain scanner and peered inside their skulls to see what happened when they filled their minds with happy thoughts, sad thoughts, and neutral thoughts.

When thinking happy thoughts, activity in their emotional brain cooled off, and they reported feeling better. When they focused on sad thoughts, their emotional brain fired up with more activity, a pattern that is associated with depression.

These effects aren't short term. Negative thinking effectively rewires our neural networks2, strengthening pathways in the brain to make us more likely to continue seeing the glass as half-empty. Our brain-imaging work shows that feeling bad further affects the brain, reducing activity in an area involved with self-control, judgment, and planning. This increases the odds of making bad decisions, which leads to more ANTs, which makes you feel worse. It's a downward spiral that can take a serious toll on your well-being.

Don't believe everything you think. Not only do ANTs disrupt optimal brain function, but they also tend to lie. Actually, they lie a lot and can wreak havoc in your life. In my new book, Change Your Brain, Change Your Grades, I write about Marcus, a 14-year-old who thought he was stupid and berated himself daily for having trouble with his schoolwork and doing poorly on tests. But he had an IQ of 135, placing him in the top 1% of all people. He wasn't stupid, but he did need to stop believing every stupid ANT that popped into his head.

With practice, you can learn to eliminate the ANTs. An easy way to do so is to take notice of your thoughts and recognize any negative thoughts. Whenever you feel sad, mad, worried, nervous, or out of control, write down the negative thought, identify the ANT species, and talk back to it. Talking back to the thought takes away its power.