A new study by UCL scientists published today in the journal Science suggests that each child's brain is wired to underestimate the true amount of force he or she uses on others - while accurately perceiving the amount of force he or she receives.
Sukhwinder S. Shergill (UCL) and colleagues conducted a series of "tit for tat" experiments on pairs of test subjects. When subjects were asked to alternately press each others' fingers, using the same amount of force just applied to their own fingers, the amount of force escalated quickly.
The researchers hypothesized that when the brain plans the body's movement, it might downplay the sensation of that movement. This may allow the brain to stay attuned to sensations that come from outside the body.
Shergill's team performed a second experiment, in which subjects applied force via a joystick, rather than by direct contact. This test has been shown not to use the brain's predictive machinery. As predicted, the forces generated and received matched each other more accurately.
Lead author, Dr Sukhwinder Shergill (UCL) said: "The results showed that to get same feeling of force, you need to exert more force. So, when you apply force yourself by pushing with your finger it feels less than when you use a machine. It is well known that a system in the brain de-emphasises the effects of our own actions, but this is the first time it has been measured".
He continued: "Just before you make a movement you send a signal to a specific brain region to warn it what to expect. The altered activity in this particular sensory area means that you tend to apply more force than you think. This mechanism also explains why you cannot tickle yourself--the brain already knows what sensation to expect and alters the brain activity responsible for the sensation accordingly. But when someone else tickles you there is no chance to adjust your brain perception, and you feel the full effects."
Journal
Science