The brain is always prepared for the event that’s likely to materialize in the next moment. Most of the time the expected outcome occurs. On the infrequent occasions when predictions fail—say, a light doesn’t turn on when the switch is flipped—a number of connected brain sites immediately release a cocktail of molecules that enhance a state of alertness and award the unexpected event a salience that renders it more memorable. Some events can activate a brain that’s not in a conscious state. The brains of sleeping newborns, for example, respond when the sound of a bell occurs after a series of identical tones because the bell sound is unexpected.
The detailed features of unexpected events that evoke strong feelings—for example, seeing a plane strike the World Trade Center on September 11, 2001—are remembered for many years. A team of scientists led by William Hirst studied the preservation of the schemata and thoughts that many Americans formed that day. Although less salient features were lost during the succeeding years, most adults retained remarkably accurate memories of where they were, what they were doing, who they were with, and other details about the falling buildings for as long as 10 years. These faithful representations are called “flashbulb” memories.
Unexpected events that aren’t understood evoke a state of uncertainty in infants long before snakes or spiders generate a similar state. Four-month-olds don’t expect to hear a blend of recorded…
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