U.S. scientists hint the world may soon hear of how a "separate form of memory" works, after getting sufficient data that shows some people carry on learning while they sleep as their brain gets busy while supposedly at rest.

"We speculate that we may be investigating a separate form of memory, distinct from traditional memory systems," said Kimberly Fenn, assistant professor of psychology and lead researcher on the sleep and dreams study at Michigan State University.

The subconscious mind is often mentioned in self-help and inspirational books as a source of drive and determination to realize goals. Fenn's study backs this up with the idea that brains can carry on processing information even after dozing off, which means anything that was difficult for a person while awake could be easier after a night's rest if the brain had processed information about it while that person was asleep.

The findings are highlighted in the Journal of Experimental Psychology: General.

"There is substantial evidence that during sleep, your brain is processing information without your awareness and this ability may contribute to memory in a waking state," the study says.

However, this "sleep memory" does not work in the same manner for everyone.

In their study involving over 250 people, Ms. Fenn and Zach Hambrick, associate professor of psychology, saw that some memories improved dramatically and others not at all. The study notes, this is a separate memory from that which we already know, and this is an undefined form of memory.

"You and I could go to bed at the same time and get the same amount of sleep," Ms. Fenn said, "but while your memory may increase substantially, there may be no change in mine."

She added that this could have implications on traditional intelligence tests and aptitude tests at school.

"This is the first step to investigate whether or not this potential new memory construct is related to outcomes such as classroom learning," she said, adding it also reinforces the need for a good night's sleep.

"Simply improving your sleep could potentially improve your performance in the classroom," Ms. Fenn said.

According to the National Sleep Foundation, people are sleeping less every year, with 63 per cent of Americans saying their sleep needs are not being met during the week.