The weather was a bit grim this morning; just off freezing and pouring in rain. I slipped on the mud and was soaked through in seconds, losing any insulation afforded by my leggings.  My hands soon felt like blocks of ice, but my back, which was covered with a winter running top and a light waterproof , remained dry and warm and I didn’t feel chilled.  I wasn’t even shivering, but this got me thinking exactley where we feel cold.  

I think we feel it at the back of our necks, across the shoulders and a few inches down the centre of our backs. I call it the shiver spot.  It’s where shivering seems to start.  Say you have washed in the open air or been for a swim in a cold river, and your teeth are chattering, if you pour hot water onto the shiver spot, or better still get somebody else to do it, then the chattering and shivering stops immediately.  The effect is still there if you pour warm water over your shoulders though less intense. 

But why is that?  What is special about that spot?  Well in animals it is the major subcutaneous site of brown fat, that particular type of metabolically active fat that generates heat in animals that live in temperate or cold zones. Brown adipose tissue (BAT for short) is well supplied with sympathetic nerves, which are activated by cold;  a   fall of temperature of the skin of the shiver spot of just a few degrees is enough to trigger an anticipatory thermogenic response that will prevent a drop in core temperature. This area has, as it were, a hot line to the brain. A drop in the temperature of the hands and the feet is not enough to cause a thermogenic response probably because this induces a local vasoconstriction that shunts blood away from the skin and returns it to the trunk via counter current heat exchange between the major arteries and veins in the centre of the limb. 

A fall in the temperature of the skin at the back of the neck is a much more immediate indicator of an imminent fall in core temperature because the back is more exposed – think of the way all mammals curl up in the cold.  Also that area at the back of the neck is close to blood vessels supplying that part of the brain stem that houses the life support systems of the body, so the temperature of this area must be maintained as a matter of necessity. 

But what about a rise in temperature? Does this area also stimulate heat loss?  I don’t think it does.  But if not, is there any sweat spot.  Might it be the mouth?  Foods that produce a sensation of heat in the mouth stimulate sweating immediately.  Does gustatory sweating have any role in temperature regulation?  Or is there another area?  Does anybody know?

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