The findings suggested we lose about one per cent of our brain cells per year through adulthood, meaning that the brains of the elderly were estimated to have lost between 35 per cent to 55 per cent of their peak number.

But when neuroscientist Suzana Herculano-Houzel devised a new way to count brain cells, she came up with a different number — 86 billion. Herculano-Houzel, now an associate professor of psychological science at Vanderbilt University, describes her research and explains how we “lost” 14 billion neurons overnight.

Every second, 32,000 neurons — brain cells — die; that’s 1.9 million in a minute. In that same minute, your brain loses 14 billion synapses, the vital intersections between neurons. Also lost in that minute are 7.5 miles of myelinated fibers through which thoughts pass.

When these neurons die, people lose their capacity to remember and their ability to do everyday tasks. Physical damage to the brain and other parts of the central nervous system can also kill or disable neurons.

The overall volume of the brain begins to shrink when we’re in our 30s or 40s, with the rate of shrinkage increasing around age 60. But, the volume loss isn’t uniform throughout the brain — some areas shrink more, and faster, than other areas.

Not getting a good night’s sleep might be linked to shrinkage of the brain’s gray matter over time, new research suggests. Faster deterioration of three parts of the brain was seen in mostly older adults who had poor sleep quality, though not necessarily too little sleep.

So on average, we don’t get “dumber” as we age—but numerous replicated studies reveal we do take longer to be as smart as we always were and we have a harder time concentrating.

12 ways to keep your brain young

1. Get mental stimulation.
2. Get physical exercise.
3. Improve your diet.
4. Improve your blood pressure.
5. Improve your blood sugar.
6. Improve your cholesterol.
7. Consider low-dose aspirin.
8. Avoid tobacco.