Hardwiring Happiness: The Practical Science of Reshaping Your Brain—and Your Life

This is a problem because the hippocampus helps you put things in perspective while also calming down your amygdala and telling your hypothalamus to quit calling for stress hormones.29

Because they lived in small bands, it was uncommon for them to meet people they didn’t know, and often dangerous when they did. While some bands interacted peacefully with each other, on average about one in eight men died in conflicts between bands, compared to one in a hundred men who died due to warfare in the twentieth century.

the cortisol in your brain overstimulates, weakens, and eventually kills cells in your hippocampus, gradually shrinking it.

Our ancestors could make two kinds of mistakes: (1) thinking there was a tiger in the bushes when there wasn’t one, and (2) thinking there was no tiger in the bushes when there actually was one. The cost of the first mistake was needless anxiety, while the cost of the second one was death.

positive experiences use standard-issue memory systems, in which new information must be held in short-term buffers long enough for it to transfer to long-term storage. “Long enough” depends on the experience and the person, but loosely speaking it’s at least a few seconds, and the longer the better.

to help our ancestors survive, the brain evolved a negativity bias that makes it like Velcro for bad experiences but Teflon for good ones.

As they say in neuroscience: Neurons that fire together wire together. Mental states become neural traits.

Over time, negative experiences make the amygdala even more sensitive to the negative. This snowballing effect occurs because the cortisol that the amygdala signals the hypothalamus to call for enters the bloodstream and flows into your brain, where it stimulates and strengthens the amygdala.

If you fail to get a carrot today, you’ll have another chance to get one tomorrow, but if you fail to avoid a stick today—whap!—no more carrots forever.

each person has the power to change his or her brain for the better—what Jeffrey Schwartz has called self-directed neuroplasticity.