They say time flies when you’re having fun, but new research shows this isn’t exactly the case. Duke University researchers have figured out why time seems to stand still when we’re kids and speed up as we age.

The differences between memories as a child versus memories as an adult really come down to how images are observed. The researchers say images are observed and processed by the brain at a slower speed as we age. This helps explain why some memories from childhood seem deeper or more vivid than newer ones.

In the same way that our relationships and lives have gotten arguably more complex since childhood, so have our neurons. As the web of neurons becomes tangled in our heads, it leads to a longer path for the signals to take.

Truth be told, these signals are pretty lazy. And we create more work for them as we age by increasing the length of the paths they want to take to our brains. The result? Older people view fewer images than a child in a similar amount of time, leading to the misconception that time is moving faster as we age.

Our minds function off a different record of time than a traditional clock. Our brain doesn’t run on hours and minutes like the rest of our lives. Instead, it relies on mental images from sensory organs to give it the perception of passing time.

The researchers looked at the eye movements of infants compared with those of adults and found children move their eyes significantly more often as they process information at a much faster rate.

So, it turns out that slowing down time has more to do with age and neurons than it does with having less fun. But at least as you get older, you appreciate it more.