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March 24, 2008

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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 Rod­ri­go 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.

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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, if not the most. 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 what, essentially, is a private feeling. 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. They were asked to state 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,” he 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 pnas. 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.