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After anesthesia, “primitive” consciousness awakens first

April 4, 2012
Courtesy of the Academy of Finland
and World Science staff

Our con­fused first wak­ing mo­ments af­ter gen­er­al an­es­the­sia rep­re­sent a ru­di­men­ta­ry form of con­scious­ness that arises from an­cient brain struc­tures, new re­search con­cludes.

The sci­en­tists in­volved de­scribed this mud­dled men­tal state as a “prim­i­tive” con­scious­ness based on deep brain struc­tures that hu­mans pos­sess in com­mon with many an­i­mals. 

PET scan find­ings are said to show that the emer­gence of con­scious­ness af­ter an­es­the­sia is as­so­ci­at­ed with ac­ti­va­tion of deep, an­cient brain struc­tures. The cross-sections above show this ac­ti­va­tion as red-yellow ar­eas in the an­te­ri­or cin­gu­late cor­tex (i), thal­a­mus (ii) and the brain stem (iii). (Credit: Tur­ku PET Cen­ter)


The in­ves­ti­gat­ors didn’t take on the more diffi­cult ques­tion of whe­ther this vague aware­ness act­ually re­sem­bles an­i­mal con­scious­ness. But they did say that stud­ies of the an­es­the­tized brain could shed light on how that mys­te­ri­ous qual­ity, con­scious­ness, arises in our brains and emerged in ev­o­lu­tion. 

The re­search­ers used scans to ex­am­ine vol­un­teers’ brains as they woke from gen­er­al an­es­the­sia. Mean­while, the ex­pe­ri­menters who had awo­ken them as­sessed their lev­el of aware­ness, based on their re­sponses to a spo­ken com­mand.

“The cen­tral, co­re struc­tures of the more prim­i­tive brain struc­tures… ap­peared to be­come func­tion­al first, sug­gest­ing that a founda­t­ional prim­i­tive con­scious state must be re­stored be­fore high­er-or­der con­scious ac­ti­vity can oc­cur,” ex­plained Har­ry Scheinin of the Uni­vers­ity of Tur­ku in Fin­land, who led the stu­dy. 

The brain ar­eas in­volved in these fuzzy early stages of aware­ness are known as the brain stem, thal­a­mus, hypothal­a­mus and the an­te­ri­or cin­gu­late cor­tex, he ex­plained. This ex­cludes the out­er re­gion of the brain, called the cor­tex, which is a rel­a­tively re­cent ev­o­lu­tion­ary de­vel­op­ment most fully de­vel­oped in hu­mans.

Twen­ty-two young, healthy vol­un­teers went un­der an­es­the­sia for the study us­ing ei­ther of two pow­er­ful anes­thet­ics, dexme-detomidine or propo­fol. The first is used as a sed­a­tive in in­ten­sive care; its ef­fect is thought to closely re­sem­ble nor­mal sleep, as it can be re­versed with mild stimula­t­ion or loud voices at nor­mal doses. Propo­fol is widely used for gen­er­al an­es­the­sia, and is al­so the sub­stance that—im­properly used as an all-around sleep aid—was al­legedly con­nect­ed to pop sing­er Mi­chael Jack­son’s death.

De­spite dif­fer­ences be­tween the drugs, the brain pro­cesses seen in the wak­ing vol­un­teers were si­m­i­lar in both cases, said the in­ves­ti­ga­tors, who re­ported their find­ings in the April 4 is­sue of The Jour­nal of Neu­ro­sci­ence. As full aware­ness bloomed, the “prim­i­tive” brain ar­eas be­came linked through elec­tri­cal nerve ac­ti­vity with more ad­vanced ar­eas called the front­al and in­fe­ri­or pa­ri­e­tal cor­tex. The type of brain scan­ning used was pos­i­tron emis­sion to­mog­ra­phy, which em­ploys rad­ia­t­ion, or nu­clear med­i­cine im­ag­ing, to pro­duce three-di­men­sion­al, col­or im­ages of pro­cesses with­in the body.

Show­ing which brain mech­a­nisms are in­volved in the emer­gence of the con­scious state is an im­por­tant step for­ward in the sci­en­tif­ic ex­plana­t­ion of con­scious­ness, ac­cord­ing to the re­search­ers. Yet much harder ques­tions re­main, they stressed: how and why these neu­ral mech­a­nisms cre­ate the sub­jec­tive feel­ing of be­ing, the aware­ness of self and en­vi­ron­ment, that char­act­er­ize con­scious­ness.


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Our confused first waking moments after general anesthesia represent a rudimentary form of consciousness that arises from ancient brain structures, new research concludes. The scientists involve described this muddled mental state as a “primitive” consciousness based on deep brain structures that humans possess in common with many animals. The scientists haven’t gone as far as to claim this vague awareness resembles animal consciousness. Studies of the anesthetized brain could shed light on how the mysterious quality of awareness arises in our brains and in evolution, the investigators added. They used scans to examine volunteers’ brains as they woke from general anesthesia and as experimenters who had awoken them assessed their level of awareness, based on their responses to a spoken command. “The central core structures of the more primitive brain structures… appeared to become functional first, suggesting that a foundational primitive conscious state must be restored before higher order conscious activity can occur,” said Harry Scheinin of the University of Turku in Finland, who led the study. The brain areas involved in these muddled early stages of awareness are known as the brain stem, thalamus, hypothalamus and the anterior cingulate cortex, he explained. This excludes the outer region of the brain, called the cortex, which is a relatively recent evolutionary development most fully developed in humans. Twenty-two young, healthy volunteers went under anesthesia for the study using either of two powerful anesthetics, dexme-detomidine or propofol. The first is used as a sedative in intensive care; its effect is thought to closely resemble normal sleep, as it can be reversed with mild stimulation or loud voices at normal doses. Propofol is widely used for general anesthesia, and is also the substance that—improperly used as an all-around sleep aid—was allegedly connected to pop singer Michael Jackson’s death. Despite differences between the drugs, the brain processes seen in the waking volunteers were similar in both cases, said the investigators, who reported their findings in the April 4 issue of The Journal of Neuroscience. As volunteers came into full awareness, the “primitive” brain areas became linked through electrical nerve activity with more advanced areas called the frontal and inferior parietal cortex. The type of brain scanning used was positron emission tomography, which uses radiation, or nuclear medicine imaging, to produce three-dimensional, color images of processes within the body. Showing which brain mechanisms are involved in the emergence of the conscious state is an important step forward in the scientific explanation of consciousness, according to the researchers. Yet much harder questions remain, they stressed: how and why these neural mechanisms create the subjective feeling of being, the awareness of self and environment the state of being conscious.