Each participant was over the age of 60, and half had practiced yoga - an ancient Indian science - for at least 15 years, Healthday reports.
Study author Elisa Kozasa said: 'The yoga group presented a greater cortical thickness in brain regions involved in executive functions such as attention.'
The findings remained true after adjusting for various factors that may influence size, including education levels.
Dr Kozasa suggested the discovery, based solely on one-time brain scans, could be because yoga involves concentration - which helps to keep the brain active.
The effects of ageing
Ageing is associated with less volume in cortical areas of the brain, most notably those responsible for attention tasks.
Various evidence uncovered in recent years points to a strong link between good memory and a thicker prefrontal cortex.
But Dr Kozasa was quick to stress that it's 'too soon to state that yoga can protect your brain against dementia'.
But researchers were skeptical of the findings, published in the journal Frontiers in Aging Neuroscience.
However, they said that more research is needed to accurately measure the effects of yoga on the brain.
Other studies saying the same
It isn't the first time that yoga has been found to keep the mind sharp. Australian scientists made a similar discovery last May.
They noted how stretching and meditation appeared to work better at preventing dementia than brain training games.
YOGA TO PREVENT CANCER
Yoga and meditation reduce our risk of cancer by changing our DNA, research revealed in June.
People who practice so-called mind-body interventions produce lower amounts of molecules that activate inflammation-causing genes.
Inflammation has long been linked to cancer, accelerated ageing and poor mental health.
Lead investigator Ivana Buric from the University of Coventry, said: 'Millions of people around the world already enjoy the health benefits of MBIs like yoga or meditation.
'But what they perhaps don't realise is that these benefits begin at a molecular level and can change the way our genetic code goes about its business.'
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