DID executioners feel a neck twinge when the guillotine met its mark? Very possibly.
Salvatore Aglioti and colleagues at La Sapienza University in Rome report that both observers and victims of pain exhibit the same physical reactions.
Volunteers were shown videos of a needle being inserted into someone鈥檚 hand or foot while electrodes on their skin measured the activity of muscles in their own hands and feet to see if they behaved in the same way as someone actually feeling pain in those places.
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To reveal the physical effects of watching the needle pricks, the researchers used a technique called transcranial magnetic stimulation to trigger muscle twitches in subjects by inducing electrical field changes in parts of the brain that control movement. Previous studies showed that when people actually experience pain in a particular muscle, the induced twitching in the same muscle diminishes.
This 鈥渇reeze鈥� response may reduce further pain by limiting movement. Aglioti鈥檚 team found that the 鈥渇reeze鈥� also happens in the same muscles when subjects see others being hurt (Nature Neuroscience, DOI: 10.1038/nn1481).
