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Emotional states or moods are produced by the various neuropeptide ligands, and what we experience as an emotion or a feeling is also a mechanism for activating a particular neuronal circuit—simultaneously throughout the brain and body—which generates a behavior involving the whole creature, with all the necessary physiological changes that behavior would require.
Think of the brain as a machine for not merely filtering and storing this sensory input, but for associating it with other events or stimuli occurring simultaneously at any synapse or receptor along the way—that is, learning.
Cortisol takes over for epinephrine and signals the liver to make more glucose available in the bloodstream, while at the same time blocking insulin receptors at nonessential tissues and organs and shutting down certain intersections so the fuel flows only to areas important to fight-or-flight. The strategy is to make the body insulin-resistant so the brain has enough glucose. Cortisol also begins restocking the shelves, so to speak, replenishing energy stores depleted by the action of epinephrine. It converts protein into glycogen and begins the process of storing fat...If this process continues unabated, as in chronic stress, the action of cortisol amasses a surplus fuel supply around the abdomen in the form of belly fat.
“The mind is so powerful that we can set off the [stress] response just by imagining ourselves in a threatening situation,” writes Rockefeller University neuroscientist Bruce McEwen in his book The End of Stress as We Know It. In other words, we can think ourselves into a frenzy.
imagining an act and doing it are not as different as they sound. When people close their eyes and visualize a simple object, such as the letter a, the primary visual cortex lights up, just as it would if the subjects were actually looking at the letter a. Brain scans show that in action and imagination many of the same parts of the brain are activated. That is why visualizing can improve performance.
Pascual-Leone found that both groups learned to play the sequence, and both showed similar brain map changes. Remarkably, mental practice alone produced the same physical changes in the motor system as actually playing the piece. By the end of the fifth day, the changes in motor signals to the muscles were the same in both groups, and the imagining players were as accurate as the actual players were on their third day.
Pain and body image are closely related. We always experience pain as projected into the body. When you throw your back out, you say, “My back is killing me!” and not, “My pain system is killing me.” But as phantoms show, we don’t need a body part or even pain receptors to feel pain. We need only a body image, produced by our brain maps. People with actual limbs don’t usually realize this, because the body images of our limbs are perfectly projected onto our actual limbs, making it impossible to distinguish our body image from our body. “Your own body is a phantom,” says Ramachandran, “one that your brain has constructed purely for convenience.”
Merzenich thinks our neglect of intensive learning as we age leads the systems in the brain that modulate, regulate, and control plasticity to waste away.
And if maps could change, thought Merzenich, then there was reason to hope that people born with problems in brain map–processing areas—people with learning problems, psychological problems, strokes, or brain injuries—might be able to form new maps if he could help them form new neuronal connections, by getting their healthy neurons to fire together and wire together.
“…conversely, exercise unleashes a cascade of neurochemicals and growth factors that can reverse this process, physically bolstering the brain’s infrastructure. In fact, the brain responds like muscles do, growing with use, withering with inactivity. The neurons in the brain connect to one another through “leaves” on treelike branches, and exercise causes those branches to grow and bloom with new buds, thus enhancing brain function at a fundamental level.”