Chilly? Meet the Brrrain's Shiver Center

Dec. 18, 2007 -- Shivering in the winter cold? Scientists now know how the brain decides it's time to start shivering.

New research shows that in extreme cold, a brain area called the lateral parabrachial nucleus tells another brain region, called the preoptic area, that it's cold enough to start shivering.

Shivering heats the skeletal muscles and "requires quite a bit of energy," says Kazuhiro Nakamura, PhD, in a news release.

For that reason, shivering is "usually the last strategy the body uses to maintain its internal temperature to survive in a severe cold environment," says Nakamura, who works at the Neurological Sciences Institute at Oregon Health & Science University.

Nakamura and Shaun Morrison, PhD, studied the science of shivering in rats.

Some of the rats were housed in cages at a balmy 75 degrees Fahrenheit. Other rats spent four hours with their lab thermostat lowered to 39 degrees Fahrenheit.

In the cold temperatures, the rats shivered, huddled together, and ate food. But they didn't show any signs of discomfort, anxiety, or pain, according to the researchers.

Chemical tracers injected into the rats linked shivering to the lateral parabrachial nucleus and, in turn, to the preoptic area.

In other words, cold temperatures set off a brain chain reaction that led to shivering.

"Other strategies to defend against the cold, such as reducing heat loss to the environment by restricting blood flow to the skin, also appear to be controlled by the sensory mechanism that we found," says Nakamura.

The study appears in Nature Neuroscience's advance online edition.