(HealthDay is the new name for HealthScoutNews.)
THURSDAY, July 10, 2003 (HealthDayNews) -- New insight into why playground fights escalate may also shed light on why schizophrenics hear imaginary voices.
British researchers have just completed a study showing your brains are wired to underestimate how much force you are inflicting on others, while accurately perceiving how much you are taking. The findings appear in the July 11 issue of Science.
Children and adults alike are familiar with the cycle of escalation that takes place between children (not to mention countries). One child taps another. The second child pushes back. The first child throws a left hook. Soon children are sobbing, noses are bloody and mothers are running.
To try to understand what, neurologically, takes place during such force escalation, the researchers conducted a tit-for-tat experiment using six pairs of young adults. The left forefinger of each person was hooked up to a small force transducer so as to precisely measure the amount of force applied. One member of each pair applied pressure to the other's left index finger. Each person was then instructed to return the favor, using the same force that was given. The participants went back and forth and responses quickly escalated.
When the subjects were asked to apply force via a joystick (pushing up for more pressure and down for less), the pressure given and received matched each other much more accurately.
"When you're about to make a movement, a signal is sent that reduces activity in the sensory area of your brain; you [therefore] have to press a bit harder to get the same feeling," says study author Dr. Sukhwinder Shergill, a senior lecturer at the Institute of Neurology at University College London and at the Institute of Psychiatry at Kings College London. "You send a signal to the appropriate sensory area to make it aware that you're about to make a movement and to identify the ownership of the action so you know that the action belongs to you."
What seems to be happening is that, just before you make a movement, your body sends a warning signal to the brain. That signal causes you to apply more force than you think. You know it's coming. This also explains why you can't tickle yourself, because your brain would be warned in advance.
One principle at work here is the ability to differentiate between an internal event and an external event. "If you have a sensation in your body, this [neurological] system allows you to clarify whether it is arising as a consequence of your doing something or a consequence of something else that might be a threat," Shergill says. "You need to be able to pick out things that are externally driven from those accidentally caused by yourself."
The response probably has an evolutionary advantage. "It's protective," says Dr. Eric Braverman, director of PATH Medical in New York City. "It's designed as a survival instinct: 'I've got to kill you before you kill me.'"
Shergill actually undertook this research not to cut down on the number of playground fights, or even wars, in the world. His main interest is its relation to schizophrenia.
"Patients with schizophrenia have these experiences where their hand moves and they say 'I'm not doing that' or they may hear thoughts or voices inside their head they believe are from someone else," Shergill explains. "The most parsimonious explanation is that they are misinterpreting their own movements. If this [brain] mechanism is going wrong, you could see how these experiences would arise."
Identifying the parts of the brain involved in these signaling processes would be a very early step towards correcting the problem.
More information
To learn more about schizophrenia, visit the National Institute of Mental Health or the National Alliance for Research on Schizophrenia and Depression.
