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

by Kelly McGonigal

Even more stunning was the finding that all human brains, at rest, slip into a similar state. Neuroscientists dubbed this pattern of brain activity the default. Left to its own devices, the human mind holds imaginary conversations, replays past experiences, and reflects on the future. It especially likes to think about you, your goals in life, and your relationships with others. This default state is essential for functioning in a social world. The brain’s baseline activity is also how we remember who we are. Its inner chatter and imagery provides the awareness that you exist as a specific individual, with preferences, aspirations, and problems, one who continues across time and context. You wouldn’t want the alternative—a brain that struggles to create a coherent sense of self or place in the world. That is what happens in late-stage Alzheimer’s disease, when pathological tangles ravage the core structures of the default network. However, the default state also has a downside. 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 acti...