Mild cognitive impairment

Mild cognitive impairment is a middle ground between normal aging and dementia. Memory, or some other mental ability, slips more than age alone would explain. But it doesn't reach the level of dementia: the person still handles daily life on their own. It's classified as a neurocognitive disorder, meaning a problem with the functions the brain uses to think and remember.

What's going on inside? It isn't the same in everyone, but when researchers compare brains with this impairment to brains without it, they find changes in specific areas. In the entorhinal cortex, a strip of the brain right next to the hippocampus, there are more neurofibrillary tangles: the protein tau clumps together and forms snarls, like yarn knotted up in a ball. That same area also has fewer neurons, the cells that carry the brain's signals. And in the hippocampus, a small, curled structure deep inside the brain, there are fewer synapses, the contact points where one neuron passes a message to the next.

Where it goes from here isn't set in stone, either. Sometimes it's the early stage of dementia, but other diseases can cause it too. Think of it as a station halfway down the line: from there, some people keep going all the way to dementia, some stay right where they are, and some go back to normal.