USA – Imagine that you are allowed to fly over many time zones.  You dread at the thought of getting the inevitable jet-lag, where the clock is shifted and no longer fits with the biological clock that controls your body.

Either you lie sleepless, or you are dead tired in the morning, depending on whether the journey goes to the west or east.  You get stomach problems. You become angry and grumpy.  You lose your concentration, and your physical performance level is reduced. And it gets worse over the years.

What do you do about it? 

Artificial light can trick your body into thinking that it is during the day, although it is night.  That way you can gradually adjust the circadian rhythm to suit the new location.

Flashes while you sleep

Now, researchers from Stanford University School of Medicine found a better solution, at least if you do not have photo fright. While you are sleeping, every ten seconds comes a blink, a light flash from a photo flash. The flash goes through the eyelids and the retina.

The treatment lasts an hour, but the effect on the circadian rhythm is twice as long.  It will correct the circadian rhythm within whole two hours while you sleep.

If instead you had used a steady light, the correction would only be a quarter of that, namely a little more than half an hour.  And you have to be awake.

Reason

So what is the explanation for that brief flash of light works better than a steady light?  The scientists have two proposals.

First, each ray seems much longer than two milliseconds.  The cells of the retina continue to fire pulses for several minutes after each flash of light. These pulses reach the area of the brain that controls the circadian rhythm.

The second explanation is that the cells in the retina are reset between each flash of light.  This gives the maximum sensitivity back, and the flash will have a greater effect than a steady light.