It should have been a good day for Joe Biden. After all, no charges are to be filed against the US president after an inquiry into his mishandling of classified files. But the official report from Robert Hur, the special counsel at the Department of Justice, was devastating nonetheless. Hur’s description of Biden, 81, as an “elderly man with a poor memory” who had “diminished faculties in advancing age” provoked an outraged defence from the White House. The incident has shone fresh light on the sensitive issue of older politicians and the risks that come with leaders who are long past what most countries regard as the standard age of retirement. The brutal fact is that the brain is not spared the physical decline that comes with old age, though the degree of decline varies enormously. Brain scans over the human lifespan reveal a rise and fall in brain size. From adulthood onwards, the brain starts to shrink as people lose grey and white matter. The grey matter is largely brain cell bodies, while white matter is the bundles of nerve fibres that connect neurons into functional brain circuits. In healthy ageing, the shrinkage is gradual, though it tends to speed up when people reach their 70s or 80s. In dementia, the decline becomes rapid. Even in healthy ageing, the shrinkage has consequences. “If you have less brain matter, that’s going to affect cognition, because you are losing neurons and the connections between them. The network is not going to be in as good a shape as we age,” says Prof Tara Spires-Jones at the UK Dementia Research Institute at the University of Edinburgh. “You don’t lose a huge number of neurons, but you do lose connections between them in various regions of the brain, and that probably plays a big part in why we are not thinking as well.” There is no wholesale decline in mental capability, however. Memory and cognition tests paint a more nuanced picture. People vary tremendously, but general knowledge tends to hold up. Vocabulary often improves past retirement age. Many other skills do worsen, though. Working memory – tasks such as remembering phone numbers – tends to weaken. People find it harder to learn new information. Old brains simply work more slowly. The consequences can be most stark when people try to recall information. The knowledge is buried somewhere in the brain, but retrieval can get sluggish in older age. It is sometimes seen when an older team takes on a younger team on University Challenge, says Dennis Chan, a consultant neurologist and professor at University College London’s Institute of Cognitive Neuroscience. “You can hear the older people groaning. They know the answer, but they can’t recall it,” he says. Hur makes specific, unflattering mention of Biden’s memory in his 345-page report, noting it would be hard to persuade jurors that Biden knew he was wrong, speculating that his lawyers would probably stress the “limitations of his recall”. Another skill that declines with age is attention; our ability to focus on a particular thought or task. Ever found yourself in the kitchen with no recollection why you went there? Or forgotten where you put your car keys? Or put the milk back in the cereal cupboard rather than the fridge? Such lapses tend to become more common in older age, though there can be other reasons beyond a faltering brain. “It can happen more often when you’re older because you have more things to think about,” says Chan. “It can be ageing, but there are other factors, such as having lots of things on your mind, stress, or lack of sleep. It isn’t necessarily pathological.” While some mental decline is on the horizon for most, research points to a number of actions people can take to ensure their brain remains healthy into old age. Doctors advise that what is good for the heart is good for the brain. That means no smoking or excessive drinking, a healthy diet and regular physical exercise. This helps to keep the cardiovascular system healthy, which is crucial for a healthy brain. But stimulation is vital, too. Chan recommends people keep challenging themselves mentally and encourages frequent socialising, because social interactions are so mentally demanding. He stresses the importance of novel activities because these force the brain to make new connections. “Doing something different to the usual is much more challenging for the brain,” Chan says. “And the more we engage our brain, the more we encourage it to grow new synapses, new connections, and that will all help.”