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Not getting sleepy? Brain scans may reveal why some can’t be hypnotized

Oct. 5, 2012
Courtesy of Stanford University Medical Center
and World Science staff

Not eve­ry­one can be hyp­no­tized, and a new study shows how the brains of such peo­ple dif­fer from those who can easily be.

Re­search­ers found that in peo­ple who could­n’t be hyp­no­tized, brain cell net­works as­so­ci­at­ed with ex­ec­u­tive con­trol on the one hand, and at­ten­tion on the other showed less ac­ti­vity and less ten­den­cy to in­ter­con­nect.

The stu­dy, pub­lished in the Oc­to­ber is­sue of Ar­chives of Gen­er­al Psy­chi­a­try, em­ployed brain scan­ning tech­niques known as func­tion­al and struc­tur­al mag­net­ic res­o­nance im­ag­ing.

“There’s nev­er been a brain sig­na­ture of be­ing hyp­no­tized, and we’re on the verge of iden­ti­fy­ing one,” said Da­vid Spie­gel, the pa­per’s sen­ior au­thor, a psy­chi­a­trist who di­rects the Cen­ter for In­te­gra­tive Med­i­cine at Stan­ford Uni­vers­ity School of Med­i­cine in Cal­i­for­nia. Such an ad­vance would help sci­en­tists bet­ter un­der­stand the mech­a­nisms of hyp­no­sis and its use­ful­ness in med­i­cine, he added.

Spie­gel es­ti­mates that a fourth of pa­tients he sees can’t be hyp­no­tized, though this char­ac­ter­is­tic is­n’t linked to any spe­cif­ic per­son­al­ity trait. Hyp­no­sis is de­scribed as a trance-like state dur­ing which a per­son has a height­ened fo­cus and con­centra­t­ion. It has been shown to help with brain con­trol over sensa­t­ion and be­hav­ior, and has been used to help pa­tients man­age pain, con­trol stress and anx­i­e­ty and com­bat pho­bias, Spie­gel said. Hyp­no­sis works by mod­u­lat­ing ac­ti­vity in brain re­gions as­so­ci­at­ed with fo­cused at­ten­tion, he added.

Al­tered “func­tion­al con­nec­ti­vity” among nerve cells in two ar­eas of the brain may “un­der­lie hyp­no­ti­z­ab­ility,” the re­search­ers wrote in their pa­per. These areas are called the dor­so­lat­er­al pre­fron­tal cor­tex and the dor­sal an­te­ri­or cin­gu­late cor­tex.

Spie­gel and col­leagues per­formed scans of the brains of 12 adults with high hyp­no­ti­z­ab­ility and 12 with low hyp­no­ti­z­ab­ility. The re­search­ers looked at the ac­ti­vity of three dif­ferent net­works in the brain: the “default-mode” net­work, used when one’s brain is idle; the “ex­ec­u­tive-con­trol net­work,” in­volved in mak­ing de­ci­sions; and the “sa­li­ence net­work,” which is in­volved in de­cid­ing some­thing is more im­por­tant than some­thing else.

Both groups had an ac­tive default-mode net­work, but highly hyp­no­tiz­a­ble par­ti­ci­pants showed great­er co-ac­tiva­t­ion be­tween com­po­nents of the ex­ec­u­tive-con­trol net­work and the sa­li­ence net­work, Spie­gel said. More spe­cif­ic­ally, in the brains of the highly hyp­no­tiz­a­ble group the left dor­so­lat­er­al pre­fron­tal cor­tex, an ex­ec­u­tive-con­trol re­gion of the brain, ap­peared to be ac­tivated in tan­dem with the dor­sal an­te­ri­or cin­gu­late cor­tex, which is part of the sa­li­ence net­work and plays a role in fo­cusing of at­ten­tion. By con­trast, lit­tle func­tion­al con­nec­ti­vity was found be­tween these two ar­eas of the brain in those with low hyp­no­ti­z­ab­ility.

Spie­gel said he was pleased to find such clear re­sults. “The brain is com­pli­cat­ed, peo­ple are com­pli­cat­ed, and it was sur­pris­ing we were able to get such a clear sig­na­ture,” he ex­plained.

He added that the work con­firms hyp­no­ti­z­ab­ility is less about per­son­al­ity than cog­ni­tive style. “We’re see­ing a neu­ral trait,” he said. The au­thors’ next step is to fur­ther ex­plore how these func­tion­al net­works change dur­ing hyp­no­sis. Spie­gel and his team have re­cruited high- and low-hyp­no­tiz­a­ble pa­tients for an­oth­er study dur­ing which scans will be as­sessed dur­ing hyp­not­ic states.

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Not everyone can be hypnotized, and a new study shows how the brains of such people differ from those who can easily be. Using brain scans, researchers found that in people who couldn’t be hypnotized, networks of brain cells associated with executive control and attention showed less activity and less tendency to interconnect. The study, published in the October issue of Archives of General Psychiatry, employed brain scanning techniques known as functional and structural magnetic resonance imaging. “There’s never been a brain signature of being hypnotized, and we’re on the verge of identifying one,” said David Spiegel, the paper’s senior author, a psychiatrist who directs the Center for Integrative Medicine at Stanford University School of Medicine in California. Such an advance would help scientists better understand the mechanisms of hypnosis and its usefulness in medicine, he added. Spiegel estimates that a fourth of patients he sees can’t be hypnotized, though this characteristic isn’t linked to any specific personality trait. Hypnosis is described as a trance-like state during which a person has a heightened focus and concentration. It has been shown to help with brain control over sensation and behavior, and has been used to help patients manage pain, control stress and anxiety and combat phobias, Spiegel said. Hypnosis works by modulating activity in brain regions associated with focused attention, he added. Altered “functional connectivity” among nerve cells in two areas of the brain may “underlie hypnotizability,” the researchers wrote in their paper. These reas are called the the dorsolateral prefrontal cortex and the dorsal anterior cingulate cortex. Spiegel and colleagues performed scans of the brains of 12 adults with high hypnotizability and 12 with low hypnotizability. The researchers looked at the activity of three different networks in the brain: the “default-mode” network, used when one’s brain is idle; the “executive-control network,” involved in making decisions; and the “salience network,” which is involved in deciding something is more important than something else. Both groups had an active default-mode network, but highly hypnotizable participants showed greater co-activation between components of the executive-control network and the salience network, Spiegel said. More specifically, in the brains of the highly hypnotizable group the left dorsolateral prefrontal cortex, an executive-control region of the brain, appeared to be activated in tandem with the dorsal anterior cingulate cortex, which is part of the salience network and plays a role in focusing of attention. By contrast, there was little functional connectivity between these two areas of the brain in those with low hypnotizability. Spiegel said he was pleased to find such clear results. “The brain is complicated, people are complicated, and it was surprising we were able to get such a clear signature,” he explained. He added that the work confirms hypnotizability is less about personality variables than cognitive style. “We’re seeing a neural trait,” he said. The authors’ next step is to further explore how these functional networks change during hypnosis. Spiegel and his team have recruited high- and low-hypnotizable patients for another study during which scans will be assessed during hypnotic states.