The discovery could hold the key to solving body clock mysteries
New discoveries into how the body clock works could provide clues to help combat jet lag, research suggests.
A University of Manchester team studied special cells which they say play an important role in regulating a person's body clock.
The cells had been thought to be inactive during the day - but their research found the opposite is true.
It is hoped the findings may also pave the way to combating sleep disorders triggered by body clock malfunctions.
Professor Hugh Piggins, an expert in neuroscience at the university, said the research will allow a new approach to being able to tune our daily clock.
The Manchester research turns on its head the idea that the brain keeps the body clock on track by firing more cells during daylight and very few during the night.
"The traditional model said the clock and the brain communicated to the rest of the brain via the number of electrical impulses that the brain cells were producing," Prof Piggins told the BBC World Service's Health Check programme.
"These impulses would travel around the brain, telling it what time of day it is.
"What we've found is in fact that there are at least two types of cells in this part of the brain."
These brain cells behave unlike any other cell seen so far, and contain a key gene - per1 - which allows them to sustain unusually high levels of "excitability".
The cells becoming so "excited" that they seem quiet or even dead; but then later they calm down, recover and become normally active again.
It is this activity which tells the human body when to be awake.
Prof Piggins added: "There's a lot of interest in the pharmaceutical industry, obviously, to try to develop chemical treatments to reset your daily clock to help counteract things like jetlag.
"Or, perhaps more importantly, different kind of sleep disorders for which dysfunctions in this clock are often involved."
This study marks the first time these "quiet" cells have been studied.
"This may mean that elsewhere in the brain there are cells like this that can also survive these very unusual conditions."