Stress can be memory’s best friend. But when you forget where you put the car keys, stress can also make you feel stupid. One expert, Rajita Sinha, a professor of psychiatry and neurobiology at Yale University, sorts through the effects of stress on memory, and its troubling relationship to dementia.

The Basics

People use the term “stress” loosely. Dr. Sinha defines it as the process by which we react to stimuli that are threatening, challenging or overwhelming. “It is a complex system of cortisol, adrenaline, peptides and other hormones and chemicals that help us respond, adapt and bring our bodies back to a stress-free baseline,” says Dr. Sinha, who is director of the Yale Stress Center.

Stress works on a spectrum, the psychiatrist says. At one end is controllable stress, where if you take the correct action you can regain control. “Imagine you notice the fridge is almost empty, but if you hurry you can get to the store before a forecast snowstorm hits,” she says. At the other end is uncontrollable stress. Losing your home or ending a significant relationship would fit in this category, she says. The two types often overlap.

Leaving its Mark

The brain grasps an uncontrollable threat very quickly and can retrieve relevant information immediately when presented with the same acute stress again, Dr. Sinha says. When you are out alone on a street at night, your stress response might help keep you alert the next time you are alone and feel in danger. “That experience sharpens the mind and encodes an impression,” she says.

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