Of all the forms of energy we can sense, the most fundamental is thermal energy. Given this basic source of energy, our bodies are able to function and sense a myriad of other stimuli: electromagnetic radiation (particularly visible light); vibration of air, which we experience as sound; physical contact, which we experience as touch; and chemical stimuli, which we experience as taste and smell.

The human body maintains a very narrow temperature range - averaging 98.6°F/37°C - and generally is equipped to handle temperature fluctuations in wonderfully adaptive ways. Our senses are geared to detect a lack of thermal energy or a surplus. If it is cold, the blood vessels constrict, breathing increases, and circulation in the extremities slows down to conserve heat energy in the central portions of the body. If it is warm, we breathe less. As we metabolize the food we eat, and when we exercise, we create large amounts of internal heat. This is used to maintain our temperature, with any excess being released to the environment.

The way your body generates and uses heat reflects your overall wellbeing. More heat is generated in the trunk of the body and distributed to the limbs and head through the flow of blood. Hands and feet, ears and scalp act like radiators. When you are hot they help dissipate heat; when you are cold their blood vessels constrict and send heat back to the center of the body. This happens not only in response to the temperature around you, but in emergency and chronic stress conditions as well. Faced with a life-threatening crisis, this diversion effect is helpful in providing a maximum amount of energy to the heart, lungs, brain, and muscles. Over a longer period, if stress becomes chronic, this adaptation can be more harmful than helpful. It leads to a retention of energy and is manifested by cold hands and feet. An extreme example is seen in the disorder known as Raynaud's disease, in which hands become painfully cold. Many people have a less serious form of this condition without even being aware of it. The first manifestation is consistently cold hands, even when the temperature outside is above 70°F/21°C. Later complications include migraine headaches, low blood-sugar, menstrual problems, and depression.

If you have this tendency, you can learn to consciously make your hands warmer, using methods such as visualization processes and temperature biofeedback/neurofeedback (see next article). You can monitor your hand temperature by touching your lips - a stable reference point - to note whether your hands are warm or cold. Soaking in a hot bath or taking a sauna produces relaxation in a similar way by encouraging blood to flow to the body's periphery. When this happens, your tissues expand with more blood and you experience pleasure.

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