The findings are based on 312 New Yorkers aged 65 and older, who were diagnosed with Alzheimer's disease and monitored for over 5 years.

All the patients underwent around four neurological assessments, each of which comprised a dozen separate tests of brain function.

Overall mental agility declined every year among all the patients. But each additional year of education equated to an additional 0.3 per cent deterioration.

The level of this drop off was particularly evident in the speed of thought processes and memory.

It was independent of age, mental ability at diagnosis, or other factors likely to affect brain function, such as depression and vascular disease.

One of the possible explanations for this finding is 'cognitive reserve' theory, suggest the authors.

This theory holds that the brain's ability to cope with Alzheimer's disease varies from person to person. But the amount of nerve connections (neurons) and information hubs (synapses) are likely to be more numerous in people who are highly educated.

Alternatively, the theory suggests that even if the quantity of neurons and synapses is no different, the synapses are likely to be more efficient and/or alternative circuitry is likely to be operating in those who are highly educated.

Therefore, higher education (or higher cognitive reserve) means that the brain develops the decreased mental agility of Alzheimer disease later, because it can "tolerate" changes for longer.

But the subsequent impact is likely to be greater than it would be in less educated brains, because of the higher levels of accumulated damage.

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Contact: Emma Dickinson
edickinson@bmj.com
44-207-383-6529
BMJ Specialty Journals
15-Feb-2006