Thanks for asking.

Check out -> https://www.sciencealert.com/the-brain-literally-starts-eating-itself-when-it-doesn-t-get-enough-sleep for better explanation.

Try thinking of it like the garbage being cleared out while you're asleep, versus someone coming into your house after several sleepless nights and indiscriminately tossing out your television, fridge, and family dog.

Like the cells elsewhere in your body, the neurons in your brain are being constantly refreshed by two different types of glial cell - support cells that are often called the glue of the nervous system.

The microglial cells are responsible for clearing out old and worn out cells via a process called phagocytosis - meaning "to devour" in Greek.

The astrocytes' job is to prune unnecessary synapses (connections) in the brain to refresh and reshape its wiring.

We've known that this process occurs when we sleep to clear away the neurological wear and tear of the day, but now it appears that the same thing happens when we start to lose sleep.

But rather than being a good thing, the brain goes overboard with the clearing, and starts to harm itself instead.

As to your question -->
So are those 3 hour people getting mentally destroyed quicker than the 8 hour people?

My Answer: - Yes, the astrocytes are more active in their case than those having 8 hours of sleep.