While some people claim they function perfectly on less than six hours of sleep, researchers have found that may not actually be the case.

A new study published today in Brain and Behavior looked at patterns in the brain of chronically sleep-deprived people and found they may not be aware how impaired they are when the sun is up.

Researchers from the University of Utah looked at scans of 839 patients in a functional MRI who admitted to chronic sleep deprivation, meaning they consistently slept less than six hours a night.

The researchers examined the wakefulness of “short sleepers” who reported daytime dysfunction and those who claimed they had no dysfunction. By putting the subjects in a functional MRI, they found signs that are consistent with diminished wakefulness.

Study co-author Paula Williams, an associate professor of psychology at the University of Utah, said that once in an MRI, many of these short sleepers soon started to transition to sleep.

“We saw evidence that even among people to who claim that they don’t have daytime drowsiness or effects of sleep deprivation, when you remove outside stimulation, they are stuck in [the MRI] and there is nothing to do," she told ABC News today. "They may still lose wakefulness and perhaps very quickly."

To identify transition to from wakefulness to sleep, researchers have used a distinct neural sign that is seen by combining electroencephalography (EEF) and resting fMRI. This “signature” has been explained by previous researchers as blood-oxygen-level-dependent (BOLD) and it lights up in what is known as the sensory areas of the brain -- primarily visual, motor and primary auditory. When it lights up certain areas of the brain, it signals a subject is starting to fall asleep.

Researchers found that when compared to conventional sleepers who get more than seven hours of shut eye, the short sleepers exhibited diminished wakefulness. By putting the subjects in a functional MRI, they found signs that were consistent with impaired wakefulness.

The research builds on previous work about "short sleepers" and how quickly they can transition from wakefulness to sleep. A 2014 study found that one-third of "short sleepers" fell asleep in just three minutes when placed in an MRI.

As a result, the researchers theorize that those who claim to be bright eyed and bushy-tailed while getting little sleep may actually have a false perception of how awake and aware they are.

"This is tantalizing, but there is a lot of research that needs to be done," Williams said.

The National Sleep Foundation recommends that adults aged 18 to 64 sleep 7 to 9 hours a day. The Centers for Disease Control reports that about one in three adults are not getting the recommended amount of sleep.

Scientific evidence suggests that not getting the recommended daily hours of sleep is associated with mood disturbances, weight gain, and even an increased in all-cause mortality.

Shailja Mehta is an Obstetrics and Gynecology resident at The Mount Sinai Hospital in Manhattan. She is a medical resident in the ABC News Medical Unit.