New tests in UK Biobank trial
2 May 2014 Last updated at 10:38 BST
A third of a million adults in the UK are to be invited to take part in the world's biggest study of cognitive function.
The aim of the trial, funded by the Medical Research Council, is to try to predict what factors may increase the risk of developing dementia.
All the participants will be part of UK Biobank, and previously gave DNA samples and lifestyle information.
They will be asked to do a series of memory and reasoning tests online.
The BBC's Medical Correspondent Fergus Walsh was the first person to take the latest test.