Scientists have figured out why your skin tenses up and your teeth chatter when an icy blast of wintry wind whips past: The brain’s wiring system monitors the temperature of the skin and decides when the shivering should commence.
Shivering is one of the many automatic and subconscious functions that the body performs to regulate itself. Other so-called homeostatic functions include the adjustment of breathing rates, blood pressure, heart rate and weight regulation.
Shivering is essentially the body's last-ditch effort to keep itself warm.
"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," said Oregon Health & Science University research fellow Kazuhiro Nakamura.
Nakamura and his colleagues studied rats and traced the shivering sensory pathway from the rodents' skin to specialized cells in a portion of the brain called the lateral parabrachial nucleus. These cells can then transmit information to another part of the brain, the preoptic area, which decides when the body should start shivering.
The rat research is thought to directly apply to humans because previous research has shown many parallels in how the two species sense and regulate heat.
The study, detailed in an online edition of the journal Nature Neuroscience, also found a connection between conscious and subconscious cold-sensing mechanisms.
"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 but not the same as the sensory pathway for conscious cold detection," Nakamura said. "In other words, your body is both consciously and subconsciously detecting the cold at the same time using two different but related sensory systems."
The sensory system the researchers found in the brain also seems to operate other cold-control mechanisms, such as the restriction of blood flow to the skin, Nakamura said.