When it comes to brain speed, every millisecond counts. How quickly your brain can process events around you determines how effectively you can react to and remember those events.
But with age (and certain cognitive conditions), the brain slows down. This slowing is minute, but can have major effects. When you’re driving, for example, a few milliseconds is all it might take to turn a near miss into a bad crash.
Brain speed affects memory, too. A slower brain is a “fuzzier” brain—it has trouble creating and storing clear pictures of what you see, hear, and otherwise sense. That affects your ability to remember clearly later.