"A lot of people do notice changes and get upset," Loewenstein said. "But there are others who don't notice them at all. The changes are really seen by those around them. We don't know what other colleagues saw and we may never know. But even when certain people are aware, they tend to downplay it."
Age is a risk factor for Alzheimer's. And at 69, Ronald Reagan was the oldest man to be elected president. During his campaign, he pledged to resign if he became "senile" – a term that refers to age-related dementia – while in office.
But without a clinical evaluation by a neuropsychologist, Alzheimer's disease in its early stages is difficult to detect, Loewenstein said.
"We're coming up with better biomarkers. And in the future, we may have better medical tests," he said.
But if you do notice cognitive changes in yourself or someone else, talking to a doctor early can make a significant difference.
"Even though there's no cure, there are treatments. The earlier you get started, the better the outcome," said Dr. Small.