Slow Pain Coming – messages from sense organs take varying lengths of time to get to the brain; experiments are included

Slow Pain Coming – messages from sense organs take varying lengths of time to get to the brain; experiments are included – Brief Article

Eric Haseltine

Some sensations take their sweet time as they travel to your brain

THERE IS A MOMENT JUST after you stub your toe when time seems to stand still. Even though you immediately sense you may have hurt yourself, more than a second goes by before you feel any pain. That’s because messages from sense organs don’t get to your brain at the same time. The speediest signals relay muscle position. They are followed by information about touch and vibration, and then by pain and temperature data. The evolutionary significance of varying signal speeds is unclear, but one theory holds that position and touch arrive earliest because they coordinate movement.

Limb position signals originating inside skeletal muscles race toward the brain at up to 390 feet per second. To catch these at work, close your eyes and wave your arms in the air. You know instantly where your arms are although you can’t see them. Touch signals can travel as fast as 250 feet per second. Bringing up the rear are pain and temperature signals, moving as slowly as two feet per second. This disparity explains why there’s a delayed sensation of pain when you stub your toe.

To see how temperature lags behind touch, place a metal spoon on top of your bare foot: The touch of the spoon registers before its coolness does. But place the spoon in the freezer for a few minutes, and then put it on. In this case, touch and cold sensations could arrive at almost the same instant, because intense temperature sensations move nearly as fast as touch.

Vision signals also vary according to intensity. You can confirm this with two simple experiments:

1 Grab a friend, a yardstick, and a pen and paper to record results. Ask your friend to hold the yardstick vertically between your outstretched hands. Have your friend drop the yardstick three times and record how many inches of the stick pass through your hands before you grasp it. Your hands must be separated the same distance for each trial and the yardstick must start from the same height. After three trials, lower the lights until you can barely see the yardstick. Then repeat the experiment. In the dark, more of the yardstick should pass through your hands before you grab it. The dimmer visual image takes longer to get from your eye to your brain than the bright one, slowing your reaction time.

2 Varying the light intensity of the image received by either eye can create an Optical illusion. To test this out, you’ll need a washer, two feet of string, and a pair of sunglasses. Attach the string to the washer, and have your friend swing the string like a pendulum about ten feet away from you. Then, using one lens of the sunglasses to shade your left eye only, watch the pendulum’s path change from a two-dimensional are to a circular ration. This pendulum appears to swing forward and back as well as side to side, because the sunglasses slow the messages from your left eye. Your brain now registers two positions of the pendulum, rather than the one image produced by both eyes receiving the same amount of light.

Remember the pendulum and the yardstick the next time you drive through a tunnel. In the dark, delayed visual reaction increases the chance of an accident that could stimulate those slow, but always dependable, pain signals.

COPYRIGHT 1999 Discover

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