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Spray said to turn people to pushovers

May 21, 2008
Courtesy Cell Press
and World Science staff

Re­search­ers have iden­ti­fied brain cen­ters acti­vated by be­tray­al of trust—and a way to keep them quiet. 

A spray of a hor­mone, ox­y­to­cin, makes peo­ple keep trust­ing even some­one who has be­trayed them, the scientists ex­plained. They presented the findings not as a trick for, say, cheat­ing spouses to keep their part­ners coop­erative, but as an in­sight into the mind with possible cli­ni­cal value.

Thom­as Baum­gart­ner of the Uni­ver­s­ity of Zu­rich and col­leagues said their work could help re­veal the brain wir­ing be­hind trust and pos­sibly the ba­sis of so­cial dis­or­ders such as pho­bias and au­tism. The find­ings are re­ported in the May 22 is­sue of the re­search jour­nal Neu­ron.

Amygdala activation, shown in red in a cross-sec­tion of the brain in an fMRI image. (Cou­rtesy NIMH Cli­n­i­cal Brain Dis­ord­ers Branch) 
The in­ves­ti­ga­tors asked vol­un­teers to play a “trust game” in which they con­tri­but­ed mon­ey to a hu­man trus­tee, who would ei­ther in­vest it and re­turn the prof­it­s—or be­tray them and keep it all. 

Some play­ers al­so re­ceived a na­sal spray con­tain­ing the brain chem­i­cal and hor­mon ox­y­to­cin, found in pre­vi­ous stud­ies to make peo­ple more trust­ing. 

The re­search­ers found that stiffed play­ers who had re­ceived ox­y­to­cin went on trust­ing their treach­er­ous part­ners. Play­ers who had re­ceived an in­ac­tive spray in­stead of ox­y­to­cin did not. 

Ox­y­to­cin was al­so found to re­duce ac­ti­vity in two brain re­gions: the amyg­da­la, which pro­cesses fear, dan­ger and pos­sibly risk of so­cial be­tray­al; and an ar­ea of the stria­tum, part of the cir­cuit­ry that guides and ad­justs fu­ture be­hav­ior based on re­ward feed­back.

These ox­y­to­cin-as­so­ci­at­ed changes, re­search­ers said, oc­curred only when play­ers be­lieved an ac­tu­al per­son was mak­ing the de­ci­sions about their mon­ey. The changes did­n’t oc­cur in a sep­a­rate “risk game,” where sub­jects were told a com­put­er would ran­domly de­cide wheth­er their mon­ey would be re­paid or not.

Play­ers’ brains were scanned us­ing func­tion­al mag­net­ic res­o­nance im­ag­ing, or fMRI, a tech­nique in which harm­less mag­net­ic fields and ra­dio waves are used to mon­i­tor brain ac­ti­vity by map­ping blood flow in the organ.

“Our in­sights in­to the neu­ral cir­cuit­ry of trust adapta­t­ion, and ox­y­to­cin’s role in trust adapta­t­ion, may al­so con­trib­ute to a deeper un­der­stand­ing of men­tal dis­or­ders such as so­cial pho­bia or au­tism that are as­so­ci­at­ed with so­cial deficits,” the re­search­ers wrote. “In par­tic­u­lar, so­cial pho­bia (which is the third most com­mon men­tal health dis­or­der) is char­ac­ter­ized by per­sist­ent fear and avoid­ance of so­cial in­ter­ac­tions.”

The work “has sig­nif­i­cant im­plica­t­ions for un­der­stand­ing men­tal dis­or­ders where deficits in so­cial be­hav­ior are ob­served,” wrote psy­cholo­g­ist Mauri­cio Del­ga­do of Rut­gers Uni­ver­s­ity in New Jer­sey, who was not in­volved in the re­search, in a pre­view in the same is­sue of the jour­nal. Fear of be­trayal, for ex­am­ple, “could serve as a pre­cur­sor to so­cial pho­bia,” he con­tin­ued, adding that the ox­y­to­cin find­ing sug­gests “po­ten­tial clin­i­cal ap­plica­t­ions.”

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Researchers have identified brain centers triggered by betrayal of trust—and found that a spray of a hormone, oxytocin, makes people keep trusting even someone who has betrayed them. Thomas Baumgartner of the University of Zurich and colleagues said their findings help reveal the brain wiring behind trust and possibly the basis of social disorders such as phobias and autism. They published their findings in the May 22 issue of the research journal Neuron. The investigators asked volunteers to play a “trust game” in which they contributed money to a human trustee, who would either invest it and return the profits—or betray them and keep it all. Some players also received a nasal spray containing the brain chemical and hormon oxytocin, found in previous studies to make people more trusting. The researchers found that stiffed players who had received oxytocin went on trusting their treacherous partners. Other players, who had received an inactive spray instead of oxytocin, did not. Oxytocin was also found to reduce activity in two brain regions: the amygdala, which processes fear, danger and possibly risk of social betrayal; and an area of the striatum, part of the circuitry that guides and adjusts future behavior based on reward feedback. These oxytocin-associated changes, researchers said, occurred only when players believed an actual person was making the decision regarding their money. The changes didn’t occur in a separate “risk game,” where subjects were told a computer would randomly decide whether their money would be repaid or not. Players’ brains were scanned using functional magnetic resonance imaging, a technique in which harmless magnetic fields and radio waves are used to monitor brain activity by mapping blood flow in the brain. “Our insights into the neural circuitry of trust adaptation, and oxytocin’s role in trust adaptation, may also contribute to a deeper understanding of mental disorders such as social phobia or autism that are associated with social deficits,” the researchers wrote. “In particular, social phobia (which is the third most common mental health disorder) is characterized by persistent fear and avoidance of social interactions.” The work “has significant implications for understanding mental disorders where deficits in social behavior are observed,” wrote psychologist Mauricio Delgado of Rutgers University in New Jersey, who was not involved in the research, in a preview in the same issue of the journal. “Betrayal aversion, for example, could serve as a precursor to social phobia, a disorder characterized by aversion to social interactions,” he continued, adding that the oxytocin finding suggests “potential clinical applications.”