It may be that loneliness may affect systems in the brain dealing with cognition and memory, making lonely people more vulnerable to effects of age-related decline in neural pathways, he suggested.

BBC: NEWS | Health | Loneliness link with Alzheimer's

Dr Matthew Brett, of the MRC Cognition and Brain Sciences Unit in Cambridge. said there had only been limited research into the long-term effects of motherhood in humans.

BBC: Mothers 'get Alzheimers boost'

Researchers from the MRC's Cognition and Brain Sciences Unit, in Cambridge, found some children with ADHD, who had no brain damage and perfectly normal intelligence, showed left neglect as severe as that seen in some adults with substantial damage to the right side of the brain.

BBC: NEWS | Health | Left blind-spot 'gives ADHD clue'

If bapi is doing what it is supposed to in terms of reducing the levels of beta amyloid and phospho-tau, and yet not improving cognition nor reversing brain shrinkage, perhaps the whole amyloid hypothesis is flawed.

FORBES: For Pfizer-JNJ Alzheimer's Drug, It May Be Too Late To Try

In addition, we might be able to play immersive apps that incorporate the best video game mechanics into brain training programs to enhance cognition, perhaps allowing people to correct neural deficiencies and even delay the development of dementia.

CNN: How mobile tech can influence our brain

But he said the detrimental effect on cognition could be due to be attributable to poor heart and lung function affecting the brain, or directly harmful effects of smoking on brain - as well as lung - tissue.

BBC: NEWS | Health | Smoking 'is bad for your brain'