Cold? That shivering isnt all in your head
Hoping to learn about how people get hot, OHSU researchers make rats get cold
What Oregon Health and Science University neuroscientist Shaun Morrison wanted to do was find a way to study fever, particularly the out-of-control fever that often results from an immune response to infections. The type of fever that can kill.
Morrison is rewriting scientific textbooks with his chilling research into, well, shivering. He decided the way to study the brain's mechanism for increasing body temperature during illness was to study what might appear to be the opposite of fever but actually is very similar - shivering.
According to Morrison, the body's nervous system handles both shivering and fever in the same way. Both are ways the body produces heat. Another way the body does this is by constricting blood vessels near the skin, which is why cold fingers turn pale.
'The goal of all these things is to increase your body's temperature,' Morrison says.
So he decided to study how people shiver - specifically, which part of the brain tells the body's muscles to start their uncontrollable spasms. When we're cold, we sense it, and until Morrison's research was published last month, scientists assumed that our conscious awareness of being cold somehow triggered the brain to start the shivering process.
Not anymore. What Morrison has discovered is that the brain's wiring for cold detection is separate from the wiring for shivering. We shiver not because we consciously feel cold, but because a parallel unconscious part of our brain signals another part of the brain that it's time to generate more heat through shivering.
So all those shorts and T-shirted folks who think cold and shivering is all psychological, you're welcome to believe it.
But according to Morrison, when your body temperature begins to fall, you probably can't keep yourself from shivering any better than the rest of us.
Morrison basically has been able to map the brain's wiring system as it deals with extreme cold. How he made that discovery is almost as interesting as the discovery itself.
Making a lab animal shiver is not an easy matter, especially when Morrison wanted to be able to measure its brain activity at the same time. That's where a special vest Morrison devised became useful. Morrison calls it a 'hypothermic water jacket,' but it is, in fact, sleeveless.
The vest has tiny plastic tubes running through it. Morrison and colleague Kazuhiro Nakamura strapped the vest on anaesthetized rats, ran increasingly cold water through the vest and waited for the shivering to begin.
Wire electrodes were run into the neck muscles of the rats to precisely measure the electrical activity of the muscles during shivering. A glass needle so small it is invisible to the naked eye was used to inject cell-inactivating chemicals into different parts of the rat brains.
By turning off different cells in the brains of the rats and seeing which could keep a cold rat from shivering, Morrison was able to map the pathway responsible for shivering.
He discovered that signals go from temperature sensors beneath the skin to one area of the brain and then to another area called the preoptic area, which tells the body's muscles to get to work producing heat.
Work, in this case, means about four cycles a second, or 240 times a minute. At least that's the rate at which shivering human muscles expand and contract. Rats shiver at about six cycles a second.
The preoptic area of the brain - which Morrison has discovered tells the body to shiver - is, in fact, the same one that tells the body to produce a fever if it is fighting an infection.
That's where Morrison thinks his research eventually might yield its most benefit; knowing which cells are responsible for shivering and fever is only a first step, he says.
Further research, he says, might find a way to bring down even those out-of-control fevers - fevers that kill.