Going to university, then choosing a mentally demanding job may help protect the brain from the devastating impact of Alzheimer's disease on memory.
Scientists found tissue damage was much quicker to lead to memory loss in the less intellectually stimulated.
They suggest mentally tough work, or genes which help people achieve such careers, may help the brain compensate for disease.
The Italian research was published in the journal Neurology.
While there are a number of studies which, based on age and symptoms, suggest that mental stimulation can ward off Alzheimer's, there are fewer which look directly at the damage wreaked by the illness on the brain.
The team from the San Raffaele University in Milan used brain scanners to look for the distinctive "tangles" and protein deposits characteristic of Alzheimer's in 242 older people, 72 who had mild cognitive impairment, and 144 with no memory problems.
Over a 14-month period, 21 of the people with mild impairment went on to be diagnosed with Alzheimer's.
However, when the MRI scans of people with the same level of memory problems were compared, the damage was significantly more extensive in those who had been university educated, then progressed to mentally-tough careers.
According to the researchers, this meant that, somehow, the brain was managing to cope better with the disease, perhaps by creating a "cognitive reserve" which buffered against its effects.
Dr Valentina Garibotta, who led the research, said: "The brains are able to compensate for the damage and allow them to maintain functioning in spite of damage.
"There are two possible explanations - the brain could be made stronger through education and occupational challenges, or, genetic factors that enabled people to achieve higher education and occupational achievement might determine the amount of brain reserve."
A spokesman for the Alzheimer's Society said that more research was "urgently needed" to build on the findings, and perhaps find ways to help people manage their symptoms.
"This research is exciting as it is the first study to use MRI scanning extensively to show that in early Alzheimer's, people with higher education have fewer symptoms of dementia than others with the same level of damage to the brain.
"Previously, research has suggested that people with "cognitive reserve" do better at managing the symptoms of dementia, but until now there has been little physical evidence."