MRI evidence on how hypnosis works.

I just came across a paper by Cojan et al. on brain activity under hypnosis. While undergoing functional MRI, participants were instructed to prepare to move their hand. After a few seconds they were told whether or not to actually perform the movement. Some of the time, they were hypnotized and believed that their hand was paralyzed. Interestingly, when the volunteers were under hypnosis, the preparatory activity in motor cortex was normal; but there was increased activity in other regions related to attention, mental imagery and self-awareness. Moreover, the connectivity between these regions and motor cortex was enhanced, indicating that hypnosis doesn’t work by directly controlling motor activity, but rather through the effects of internal representations and self-monitoring processes on such activity. Here is the authors' summary of the work:

Brain mechanisms of hypnosis are poorly known. Cognitive accounts proposed that executive attentional systems may cause selective inhibition or disconnection of some mental operations. To assess motor and inhibitory brain circuits during hypnotic paralysis, we designed a go-nogo task while volunteers underwent functional magnetic resonance imaging (fMRI) in three conditions: normal state, hypnotic left-hand paralysis, and feigned paralysis. Preparatory activation arose in right motor cortex despite left hypnotic paralysis, indicating preserved motor intentions, but with concomitant increases in precuneus regions that normally mediate imagery and self-awareness. Precuneus also showed enhanced functional connectivity with right motor cortex. Right frontal areas subserving inhibition were activated by nogo trials in normal state and by feigned paralysis, but irrespective of motor blockade or execution during hypnosis. 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.