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The world is full of people doing Sudoku or crosswords hoping to stave off dementia. The problem? You just get good at puzzles rather than improving your thinking and memory overall. This is a much broader issue in cognitive training called distant transfer: whether you derive benefits in brain functions not closely related to the training itself.

The largest, longest study of cognitive training has recently reported its findings 20 years from the original intervention. Nearly 3,000 older people were divided into four groups: controls, memory training, cognitive speed training, and reasoning (problem-solving) training. Over several weeks, they were taught their assigned technique and given practice. After a year, some received booster sessions, and again at three years.

By 20 years, cognitive speed training still showed lower dementia risk, but Sudoku and crosswords just make you better at puzzles.

After 10 years, people who’d had reasoning and speed training had significantly maintained their cognitive performance in those areas, especially if they’d had top-up sessions. Memory training didn’t have lasting effects.

But what was really interesting was that those who’d had cognitive speed training had a lower risk of Alzheimer’s and related dementias. By 20 years, the benefits of reasoning training had faded, but the speed training group still showed a lower dementia risk.

The speed training involved a visual recognition task, and crucially, it was adaptive. The person’s skills were measured at the beginning, the programme was tailored to their starting speed, then it got progressively harder as they improved. The reason for the dementia protection isn’t known, but it may be that the brain built extra nerve circuits that acted as a defence against cognitive decline.

When choosing a cognitive training program, there are three things to look for: does it focus on processing speed, is it adaptive to ability level, and what’s the evidence base? Be wary of programs that just improve on specific tasks like crosswords or Sudoku.

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