The brains of Alzheimer's patients may start changing years before symptoms of the disease show up.
Researchers followed 136 people for five years.
All had "normal" brain function at the start of the study.
By the end, 23 developed mild cognitive impairment.
Nine went on to have Alzheimer's disease.
When researchers compared them to those who kept normal brain function, they found structural differences in the brains that were noticeable from the start of the study.