Friday, February 22, 2008

Brain cells tied to consciousness reported found

Feb. 19, 2008
Courtesy University of Leicester
and World Science staff

In a study billed as an ex­plora­t­ion in­to the realm of “con­scious­ness,” re­search­ers claim to have found brain cells that be­come very busy only when some­thing is con­sciously no­ticed.

Try­ing to un­der­stand what cre­ates con­sciousness—the sense of be­ing alive and aware—is one of the all-time most ex­as­per­at­ing prob­lems in sci­ence. The key stum­bling block: even if one knew every brain mech­an­ism un­der­ly­ing con­scious­ness, there would still be no ap­par­ent way to see or meas­ure the ac­tu­al pro­duc­tion of con­sciou­sness.

Scientists examined cells deep within the temporal lobe, the region colored in yellow in this diagram.

For now, many re­search­ers fig­ure they may as well just do the best they can in un­rav­el­ing those phys­i­cal mech­an­isms. The new stu­dy, led by Qui­an Qui­roga of the Uni­ver­s­ity of Leices­ter, U.K., is among those de­signed to at­tack that ques­tion.

Vol­un­teers were shown pic­tures on a com­put­er screen very briefly­—for a time just at the edge of be­ing long enough to be no­tice­a­ble. The par­t­ici­pants were asked each time wheth­er they saw the pic­ture or not. Some­times the ex­act same vis­u­al in­put was no­tice­a­ble on one tri­al and not on an­oth­er, for the same per­son, Qui­an Qui­roga said.

The re­search­ers ex­am­ined what was hap­pen­ing in the brain dur­ing this. Cer­tain neu­rons, or brain cells, “re­sponded to the con­scious per­cep­tion in an ‘all-or-none’ way,” Qui­an Qui­roga said: they dra­mat­ic­ally changed their rate of fir­ing sig­nals, only when pic­tures were rec­og­nized. These neu­rons were in the me­di­al tem­po­ral lobe, a re­gion deep in­side the brain of­ten as­so­ci­at­ed with mem­o­ry.

For ex­am­ple, in one pa­tient, a neu­ron in the hip­pocam­pus—a struc­ture al­so in that area—“fired very strongly to a pic­ture of the pa­tient’s broth­er when rec­og­nized and re­mained com­pletely si­lent when it was not,” Qui­an Qui­roga said. “An­other neu­ron be­haved in the same man­ner with pic­tures of the World Trade Cen­tre.” The vol­un­teers were pa­tients who had to un­dergo ep­i­lep­sy sur­gery.

“Based on the fir­ing of these neu­rons it was pos­si­ble to pre­dict far above chance wheth­er a pic­ture was rec­og­nized or not,” Quian Quiroga said. Al­so, “a pic­ture flashed very briefly gen­er­at­ed nearly the same re­spon­se—if rec­og­nized—as when shown for much long­er per­i­ods of time.”

The find­ings are to ap­pear this week in the early on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

Po­ten­tial ap­plica­t­ions of the work in­clude the de­vel­op­ment of “neu­ral pros­thet­ic” de­vices to be used by par­a­lysed pa­tients or am­putees, Quian Qui­roga said. A spi­nal in­ju­ry pa­tient, such as the late Chris­to­pher Reeve, can think about reach­ing a cup of tea, but the mus­cles don’t get the or­der. Neu­ral pros­the­ses are de­signed to read these com­mands di­rectly from the brain and trans­mit them to bi­on­ic de­vices such as a robotic arm.

The find­ings, Quian Qui­roga said, could al­so have im­plica­t­ions treat­ment of pa­tients with patholo­gies of the hip­po­cam­pal forma­t­ion, such as ep­i­lep­sy, Alzheimer’s dis­ease and schiz­o­phre­nia.