So how could focusing on your thoughts have such impressive physical effects? The assumption that meditation simply induces a state of relaxation is “dead wrong”, says Raison. Brain-imaging studies suggest that it triggers active processes within the brain, and can cause physical changes to the structure of regions involved in learning, memory, emotion regulation and cognitive processing.
The question of how the immaterial mind affects the material body remains a thorny philosophical problem, but on a practical level, “our understanding of the brain-body dialogue has made jaw-dropping advances in the last decade or two,” says Raison. One of the most dramatic links between the mind and health is the physiological pathways that have evolved to respond to stress, and these can explain much about how meditation works.
When the brain detects a threat in our environment, it sends signals to spur the body into action. One example is the “fight or flight” response of the nervous system. When you sense danger, your heart beats faster, you breathe more rapidly, and your pupils dilate. Digestion slows, and fat and glucose are released into the bloodstream to fuel your next move. Another stress response pathway triggers a branch of the immune system known as the inflammatory response.
These responses might help us to run from a mammoth or fight off infection, but they also damage body tissues. In the past, the trade-off for short bursts of stress would have been worthwhile. But in the modern world, these ancient pathways are continually triggered by long-term threats for which they aren’t any use, such as debt, work pressures or low social status. “Psychological stress activates these pathways in exactly the same way that infection does,” says Raison.