Many conversations with friends include some reference to sleep. In particular, I and my peers often wake around 3:00 am and lie there, worrying about something trivial until it is time to get up. A few years ago, I was relieved to read that the experience is widespread. Once again, the discovery arose from studies of the brain using the "functional MRI." Once again, theories of evolution cast light on the possible origin and adaptive value of a behavior pattern we now find troubling.
As a species vulnerable to predators, early humans were constantly on the lookout for foes. Many of the the four-legged hunters who coveted our caloric content were programmed to forage at night. The primitive humans who slept lightly and worried about every sound were more likely to live and pass along their genes. Those who slept more soundly enabled the predatory species to do so.
Scanning for danger comes naturally to us. So does over-reacting. We may obsess over minor physical symptoms, signs of disapproval by others, an invasion of personal space, weather, politics, and the evening news. Our responses range from becoming more cautious and self-protective to activating the aggressive instinct, challenging our perceived enemies with proactive force.
Reflexive reactions to threat in "real time" are one outcome of evolutionary attunement to negative signs. In addition, our brains are inclined to emphasize unhappy memories over happy ones, and to project that negativity into the future. Neuroscience once again looks for an evolutionary explanation. We are wired to recognize and react more intensely to "sticks" than to "carrots." Avoiding harm is a more powerful impetus to action than pursuing rewards. The threat of being killed by a predator calls for more urgent action than the desire for a full stomach or a restful nap. Storing information about past harms prepares us to see new ones quickly and to fight, freeze, or flee when they appear. Vivid and emotional memories of abuse by strangers, rejection by peers, and criticism by parents or teachers stick with us longer and rise to the surface more quickly than memories of achievement, loving encounters, beauty, and joy.
Dr. Rick Hanson calls this broad human trait the "negativity bias of the brain." He further describes the brain as having "Velcro for the bad and Teflon for the good." Hanson attributes our gloomy patterns of thought and emotion to deeply entrenched neurological pathways in the brain. Inherited connections between one neuron and the next are strengthened by experience. They powerfully affect the way we see and respond to daily events. We are born fearful, and each time we perceive and react negatively to another threat, we reinforce the neural pathways that took us there. Neurons that fire together are said to wire together.
