Saturday, March 27, 2010

Psychopaths’ brains wired to seek rewards no matter what

Psychopaths’ brains wired to seek rewards no matter what, researchers say
March 15, 2010
Courtesy Vanderbilt University
and World Science staff
“Psycho.” The very word con­jures im­ages of cold, re­morse­less cri­min­ality. But sci­ent­ists don’t ful­ly un­der­stand how the brains of psy­cho­paths—peo­ple with anti­social, em­pathy-short and some­times cri­min­al per­son­a­lities—work.

A study has now found that the brains of psy­chopaths seem to be wired to keep seek­ing a re­ward at any cost. Sci­en­tists say the re­search clar­i­fies the role of the brain’s re­ward sys­tem in psy­chop­a­thy and opens a new ar­ea of study for un­der­stand­ing what drives these twisted minds.

The study from from Van­der­bilt Uni­vers­ity in Nash­ville, Tenn. is pub­lished in the March 14 is­sue of the re­search jour­nal Na­ture Neu­ro­sci­ence.

Ab­nor­mal­i­ties in how a brain struc­ture called the nu­cle­us ac­cum­bens, high­light­ed he­re, pro­cesses dopamine have been found in peo­ple with psy­cho­pathic traits, sci­en­tists say. (Cred­it: Greg­o­ry R.Samanez-Larkin and Josh­ua W. Buck­holtz )
“Psy­chopaths are of­ten thought of as cold-blood­ed crim­i­nals who take what they want with­out think­ing about con­se­quences,” Josh­ua Buck­holtz, a grad­u­ate stu­dent in psy­chol­o­gy and lead au­thor of the new stu­dy, said. “We found that a hyper-reac­tive dopamine re­ward sys­tem may be the founda­t­ion for some of the most prob­lem­at­ic be­hav­iors as­so­ci­at­ed with psy­chop­a­thy, such as vi­o­lent crime, re­cid­i­vism and sub­stance abuse.”

Dopamine is the brain chem­i­cal most closely as­so­ci­at­ed with pleas­ure and ex­cite­ment.

Pre­vi­ous re­search on psy­chop­a­thy has fo­cused on what these peo­ple lack­—fear, em­pa­thy and in­ter­per­son­al skills. The new re­search, how­ev­er, ex­am­ines what they have in abun­dance—im­pul­siv­ity, height­ened at­trac­tion to re­wards and risk tak­ing, said Buck­holtz and his co-auth­ors. Im­por­tant­ly, the lat­ter traits are those most closely linked with the vi­o­lent and crim­i­nal as­pects of psy­chop­a­thy, re­search­ers said.

“There has been a long tra­di­tion of re­search on psy­chop­a­thy that has fo­cused on the lack of sen­si­ti­vity to pun­ish­ment and a lack of fear, but those traits are not par­tic­u­larly good pre­dic­tors of vi­o­lence or crim­i­nal be­hav­ior,” said Van­der­bilt psy­chol­o­gist Da­vid Zald, co-au­thor of the stu­dy.

“Our da­ta is sug­gest­ing that some­thing might be hap­pen­ing on the oth­er side of things. These in­di­vid­u­als ap­pear to have such a strong draw to re­ward—to the car­rot—that it over­whelms the sense of risk or con­cern about the stick.”

The re­search­ers used a brain im­ag­ing tech­nique called pos­i­tron emis­sion to­mog­ra­phy, or PET, to meas­ure dopamine re­lease, in con­cert with a probe of the brain’s re­ward sys­tem us­ing func­tion­al mag­net­ic im­ag­ing, or fMRI. “The really strik­ing thing is with these two very dif­fer­ent tech­niques we saw a very si­m­i­lar pat­tern—both were height­ened in in­di­vid­u­als with psy­cho­pathic traits,” Zald said.

Vol­un­teers for the study took a per­son­al­ity test to gauge their lev­el of psy­cho­pathic traits. These traits lie on a spec­trum: vi­o­lent crim­i­nals fall at its ex­treme end, but a nor­mally func­tion­ing per­son can al­so have psy­cho­pathic traits to some de­gree. These traits in­clude ma­ni­pu­la­tive­ness, ego­cen­tricity, ag­gres­sion and risk tak­ing.

The re­search­ers gave the vol­un­teers a dose of am­phet­a­mine, or speed, and then scanned their brains us­ing PET to view dopamine re­lease in re­sponse to the stim­u­lant. Sub­stance abuse has been shown in the past to be as­so­ci­at­ed with al­tera­t­ions in dopamine re­sponses. Psy­chop­a­thy is strongly as­so­ci­at­ed with sub­stance abuse.

“Our hy­poth­e­sis was that psy­cho­pathic traits are al­so linked to dys­func­tion in dopamine re­ward cir­cuit­ry,” Buck­holtz said. “Con­sis­tent with what we thought, we found peo­ple with high lev­els of psy­cho­pathic traits had al­most four times the amount of dopamine re­leased in re­sponse to am­phet­a­mine.”

The re­search sub­jects were lat­er told they would re­ceive some mon­ey for com­plet­ing a sim­ple task. Their brains were scanned with fMRI while they were per­form­ing the task. The re­search­ers found in those par­ti­ci­pants with more psy­cho­pathic traits the dopamine re­ward ar­ea of the brain, the nu­cle­us ac­cum­bens, was much more ac­tive while they were an­ti­cipat­ing the re­ward.

“It may be that be­cause of these ex­ag­ger­at­ed dopamine re­sponses, once they fo­cus on the chance to get a re­ward, psy­chopaths are un­able to al­ter their at­ten­tion un­til they get what they’re af­ter,” Buck­holtz said. Added Zald, “It’s not just that they don’t ap­pre­ci­ate the po­ten­tial threat, but that the an­ti­cipa­t­ion or mo­tiva­t­ion for re­ward over­whelms those con­cerns.”