Cold Enough to Start Shivering?

The brain wiring that tells your body when to start shivering is different from the pathways that let you consciously decide when you're cold, according to new research from the Oregon Health and Science University (OHSU).

By studying lab rats, researchers Kazuhiro Nakamura and Shaun Morrison were able to follow the sensory path leading from the skin to specialized cells in the brain. Those cells, located in the lateral parabrachial nucleus, send information to another portion of the brain -- the preoptic area -- that decides whether it's time for the body to start shivering.

"One fascinating aspect of this study is that it shows the sensory pathway for shivering, which can be thought of as brain wiring, is parallel to but not the same as the sensory pathway for conscious cold detection," said Nakamura, an OHSU Fellow for Research Abroad from the Japan Society for the Promotion of Science. "In other words, your body is both consciously and subconsciously detecting the cold at the same time using two different but related sensory systems."

Shivering is an automatic response set off by the brain as a way to help keep the body warm when it's very cold outside. The subconscious response is one of many automatic -- or homeostatic -- functions controlled by the brain. Other such functions, which are essential to our survival but not under our conscious control, include regulation of breathing rates, blood pressure and heart rates.

"Shivering, which is actually heat production in skeletal muscles, requires quite a bit of energy and is usually the last strategy the body uses to maintain its internal temperature to survive in a severe cold environment," Nakamura said. "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."

By better understanding the pathways that control the perception of cold and the onset of shivering, researchers might be able to help identify the source of problems in people with abnormal thermal sensation, Morrison said. The information could also provide insights into how and why our ability to sense and respond to changes in temperature declines as we age, he said.

"This research is a fundamental science discovery that furthers our knowledge about one of the many functions that our brains are constantly monitoring, responding to and adjusting to keep us alive and healthy," Morrison said.

Nakamura's and Morrison's research is published in the online edition of Nature Neuroscience.

Oregon Health and Science University, "OHSU Researchers Reveal the Science of Shivering." URL: (http://www.eurekalert.org/pub_releases/2007-12/ohs-orr121707.php)