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If your long path is short-circuited by stress, and your brain is using the short path instead, you might be so alarmed at the mere thought of a shark that you have a panic attack just thinking about taking a swim in the ocean. All the body’s machinery of FFF then gets engaged by this imaginary threat, just as if you were nose to nose with Jaws. Your gut clenches, your heart races, your breathing becomes fast and shallow, and your focus narrows to the point where you can’t think about anything other than the threat. This takes a huge biological toll on the body. High adrenaline produces dramatic reductions in life span. Stressed people have much more disease and live much shorter lives than unstressed people. Whatever form stress takes—depression, anxiety, or PTSD—correlates with higher rates of cancer, diabetes, and heart disease. The deficits in the life spans of stressed people are measured in decades rather than years. In meditators, the amygdala is quiet. It becomes even quieter with practice. The difference in amygdala activation between the longest-term meditators and their less-experienced peers has been measured. The adepts show 400% less reactivity to stressful events. But even in novices who practice mindfulness for 30 hours over 8 weeks, decreased amygdala activity is found. Other structures within the midbrain or limbic system work together with the hippocampus and amygdala. One of them, the thalamus, is like a relay station. Close to the corpus callosum, it identifies information coming in from the senses like touch, hearing, and taste, and directs it to the consciousness centers of the prefrontal cortex. The thalamus typically becomes more active during meditation, as it works harder to suppress sensory input (like “that buzzing mosquito” or “this chair is too hard”) that pulls us out of Bliss Brain. With the hippocampus regulating emotion, the thalamus regulating sensory input, and the long path in good working order, stress-inducing signals aren’t sent to the amygdala. In turn, all the body’s FFF machinery remains offline. This produces corresponding biological benefits. Heart rhythm is even. Respiration is deep and slow. Digestion is effective. Immunity is high. That’s why so many studies show pervasive health and longevity benefits among meditators.
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Dawson Church (Bliss Brain: The Neuroscience of Remodeling Your Brain for Resilience, Creativity, and Joy)