The next time you have trouble falling asleep, consider sending thoughts of warmth and sunshine to your extremities.

No, this isn't some new age mumbo jumbo. Dr. Matthew Ebben of Cornell University explains that when you sleep, the blood vessels in your hands and feet dilate so that blood can move from your core to your extremities. This sends warmth to your hands and feet while cooling your body. It also reduces your metabolic requirement while sleeping and helps to reserve energy for a time of day when your senses are more active.

Earlier Swedish research demonstrated that warm hands and feet are the single best predictor of sleep onset, trumping melatonin or even subjective feelings of sleepiness.(1) But it's not as simple as wearing mittens to bed. The warmth in your hands and feet is a marker for cooling of your body's center and the flow of temperature away from the core. Just warming the extremities physically (i.e., with mittens or socks) won't do it.

So how in the world do you cool your core and warm your extremities?

Enter biofeedback, a technique that involves using mental imagery to achieve measurable physical results such as lowering blood pressure. Biofeedback has been used successfully in over 150 medical conditions.(2)

Dr. Ebben's research used a particular type called temperature biofeedback to accomplish this "central cooling." His team attached electrodes to the hands and feet of subjects, all of whom suffered from insomnia.(3) The electrodes were attached to a computer screen and the subjects could see the readout of their temperature. Subjects were told to use whatever imagery they could to try to increase the temperature of their hands and feet.

General guidelines like "think of the sun " or "imagine the beach" were suggested. The subjects quickly learned what images worked best for them by simply watching the computer screen and monitoring the increase in temperature.

This is really one technique where it's safe to say "try this at home." Ebben suggests that those suffering with insomnia might want to get a biofeedback trainer for a couple of sessions. Or "you can buy a cheap temperature monitor for about 20 bucks that you tape to your fingers. They really work. Then you can practice at home."

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The diagnosis of insomnia is made by patient determination and self-report. There is no medical test for it.