New research shows brain training could play an important role in helping to prevent dementia.

Computer-based brain training can improve memory and mood in older adults but is no longer effective once a person has dementia, according to new research.

Brain training is a treatment for enhancing memory and thinking skills by practising mentally challenging computer-based exercises, which are designed to look and feel like video games.

Researchers from the University of Sydney's Brain and Mind Centre reviewed more than 20 years of research that in total involved 17 randomised clinical trials and nearly 700 participants.

They have shown brain training led to improvements in cognition, memory, learning and attention.

Improvements were also reported in psychosocial functioning, that is a person's mood and self-perceived quality of life.

The findings, published in the American Journal of Psychiatry, were not so positive when the researchers analysed data from 12 studies of brain training in people with dementia.

With the number of Australians living with dementia expected to increase to 400,000 in less than five years, Dr Amit Lampit from the School of Psychology says brain training could be an inexpensive and safe tool in the fight against the debilitating brain disease.

"Our research shows that brain training can maintain or even improve cognitive skills among older people at very high risk of cognitive decline," said Dr Lampit.

People with mild cognitive impairment - a decline in memory and other thinking skills despite generally intact daily living skills - are at one-in-10 risk of developing dementia within a year.

Dr Lampit believes there is enough evidence to introduce brain training within a clinical setting in the aged-care sector.