Why does your head hurt when you scarf down ice cream too quickly, or your left arm ache when your heart is in trouble? Neuroscientists think that misplaced sensations, called referred pains, arise when sensory fibers from different parts of the body connect to the same nerve cells in the spinal cord or brain stem, confusing your brain about which part of your body the message came from. And, as you are about to learn, these cross-connects are not limited to pain.
Experiment 1
Place a teaspoon of black pepper (freshly ground works best) under your nose and inhale until you sneeze. Observe that no matter how hard you try, you cannot keep your eyes open while sneezing. Just as sensory inputs streaming into your brain can sometimes become sidetracked, so too can motor impulses. In this instance, your brain’s commands to the sneeze muscles in both your diaphragm and your throat are cross-connected to the outgoing motor pathways that closed your eyes.
Experiment 2
Sit in a dark room for about five minutes, then look briefly toward the sun or a bright light. Did you feel a tickle in your nose? Did you sneeze? If so, you belong to the 18 to 35 percent of the population who suffer from a medical condition known as ACHOO (autosomal dominant compelling helio-ophthalmic outburst) syndrome. ACHOO, also commonly called the sun-sneeze response-is an inherited disorder in which sensory impulses from the optic nerve spill over into the trigeminal nerve in the nose. A strong visual signal causes itching in the nostrils, which triggers the sneeze reflex.
Experiment 3
Bring yourself to the brink of sneezing using any of the aforementioned methods, then pinch your nostrils. Chances are, you just halted the sneeze in its tracks by easing the nasal irritation enough to make the neural short circuit an ally. Similarly, rubbing a part of your body that hurts can ease the pain there. According to the gate theory of pain, touch and pain fibers are anatomically different but transmit to some of the same neurons in the central nervous system. Activity in touch-sensitive fibers can actually turn off shared central neurons, preventing pain signals from reaching the brain. You can test the gate theory by pinching your arm until it hurts, then vigorously rubbing the pinched tissue. The discomfort should diminish faster than it would have if you hadn’t rubbed.
Neural short circuits are not mere curiosities. They may explain why acupuncture often works. Researchers hope they may also lead to new treatments for migraine and other forms of chronic pain.
