June 24, 2009
Researchers Show How Hypnosis Can Paralyze Limbs
A new study is shedding light on the process that allows hypnotherapists to cause limbs to go numb.
Writing in the June 25 issue of the journal Neuron, Dr. Yann Cojan and a team of researchers from the Neuroscience Center and Medical School at the University of Geneva created an experiment to study brain activity during hypnosis-induced paralysis.
"We used functional magnetic resonance imaging to directly test whether a hypnotic suggestion of paralysis activates specific inhibitory processes and whether these may or may not correspond to those responsible for inhibition in nonhypnotic conditions," said Cojan.
Twelve participants were instructed to perform a task that involved hand movement. They were given different signals which dictated whether or not the movement was executed. Researchers used a control group of six participants who were instructed to act as if they were unable to move their hand.
The team found that during the process, the right motor cortex instructed the left hand to move as usual, but the cortex did not respond to parts of the brain typically involved in controlling limb movement, they told the Associated Press.
The motor cortex was normally activated as subjects prepared to complete the task, which researchers said suggests that hypnosis did not suppress activity in motor pathways or eliminate representation of motor intentions.
Cojan told the AP that it appeared the motor cortex "is connected to the idea that it cannot move (the hand) and so ... it doesn't send the message to move."
Additionally, researchers noted that "hypnosis affected the enhanced activation of the precuneus, a brain region involved in memory and self imagery, and with a reconfiguration of executive control mediated by the frontal lobes."
"These results suggest that hypnosis may enhance self-monitoring processes to allow internal representations generated by the suggestion to guide behavior but does not act through direct motor inhibition," explained Dr. Cojan.
"These findings make an important new step towards establishing neurobiological foundations for the striking impact of hypnosis on the brain and behavior."
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