Imaging the Hypnotized Brain Reveals Neural Mechanisms of Suggested Paralysis

Although it is known that hypnosis can affect the mind and behavior, the underlying brain mechanisms are not well understood. Now, a new study has demonstrated the influence of hypnotic paralysis on brain networks involved in internal representations and self-imagery.

Earlier studies have revealed suggestion-induced changes in brain activity underlying memory, pain perception, and voluntary movement and led to the theory that the effects of hypnosis may involve engagement of brain processes that mediate executive control and attention. However, none of these studies directly assessed whether an inhibition or disconnection of executive control systems actually caused the observed changes in neural activity.

A group of researchers from the Neuroscience Center and Medical School at the University of Geneva (Switzerland) designed an experiment to evaluate motor and inhibitory brain circuits during hypnosis-induced paralysis. "We used functional magnetic resonance imaging [fMRI] 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,” explained lead study author Dr. Yann Cojan.

Specifically, subjects performed a task where they prepared to make a hand movement in response to a cue and then, depending on the signal, did or did not execute the prepared movement. Some study participants were hypnotized with the suggestion that their left hand was paralyzed while others were instructed to simulate left hand paralysis. Dr. Cojan and colleagues found that hypnosis produced distributed changes in prefrontal and parietal areas involved in attention along with striking modifications in the functional connectivity of the motor cortex with other brain areas.

Importantly, despite the suggestion of paralysis, the motor cortex was normally activated during the preparation phase of the task. This suggests that hypnosis did not inhibit activity in motor pathways or eliminate representation of motor intentions. Hypnosis was also associated with an 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.

The researchers concluded that hypnosis induces a disconnection of motor commands from normal voluntary processes under the influence of brain circuits involved in executive control and self-imagery. "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,” stated Dr. Cojan. "These findings make an important new step towards establishing neurobiological foundations for the striking impact of hypnosis on the brain and behavior.”

The study was published in the June 25, 2009, issue of the journal Neuron.

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