The concept of cognitive reserve originated in the late 1980s, when researchers described individuals with no apparent symptoms of dementia who were nonetheless found at autopsy to have brain changes consistent with advanced Alzheimer’s disease. These individuals did not show symptoms of the disease while they were alive because they had a large enough cognitive reserve to offset the damage and continue to function as usual. Since then, research has shown that people with greater cognitive reserve are better able to stave off symptoms of degenerative brain changes associated with dementia or other brain diseases, such as Parkinson’s disease, multiple sclerosis, or a stroke. A more robust cognitive reserve can also help you function better for longer if you’re exposed to unexpected life events, such as stress, surgery, or toxins in the environment. Such circumstances demand extra effort from your brain—similar to requiring a car to engage another gear.