The Joy of Movement: How Exercise Helps Us Find Happiness, Hope, Connection, and Courage

by Kelly McGonigal

For many of us, the mind’s default has a negative bias. Its most familiar habits are to ruminate on past hurts, criticize ourselves or others, and rehearse reasons to worry. The default state can also become a mental trap. In theory, when you focus on something—a conversation, a movie, work—the default mode quiets down and allows the brain to enter a state of outwardly directed attention. But people who suffer from depression or anxiety don’t make this switch as easily. They show unusually high activity in the default mode network, and they get stuck in the default state, making it difficult to focus on anything or anyone else, or even to fall asleep. For some, the mind can even become addicted to rumination. The brain’s reward system—not a core part of the default mode network—can become highly connected to the structures within the default mode network that are associated with memories, worry, and thinking about yourself. Every time you revisit a familiar fear or judgment, the reward system says, “Yes, more of that!” It’s as though the brain is convinced that some good might come from the rehashing, worrying, or self-criticism. When this happens, you can find yourself as unable to escape these mental habits as a heroin user trying to suppress their cravings and compulsions.