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An image, or its interpretation? Newfound brain cells show surprising role

March 30, 2005
Courtesy 
and World Science staff

Sci­en­tists have iden­ti­fied some brain cells whose sig­nals re­flect our in­ter­preta­t­ion of an im­age—not so much the im­age it­self, a study has found.

The researchers pre­sented vol­un­teers with pho­tographs that lent them­selves to two in­ter­preta­t­ions: each pho­to was a cross be­tween two Hol­ly­wood celebr­i­ties. Certain in­forma­t­ion-carrying brain cells, or neu­rons, were found to fire sig­nals de­pend­ing on which ac­tor the vol­un­teer took the im­age to rep­re­sent.

Arnold Schwar­ze­neg­ger and Syl­ves­ter Stal­lone were morphed for the study. (Cre­dit: U. of Lei­ces­ter)


The find­ings echo a strand of phil­o­soph­i­cal thought known as Brit­ish Em­pir­i­cism as well as the ideas of Ar­is­tot­le, some 2,400 years ago, said Ro­drigo Quian Qui­roga, a col­la­bo­ra­tor in the stu­dy.

“As Ar­is­tot­le put it, we cre­ate im­ages of the ex­ter­nal world and use these im­ages rath­er than the sen­so­ry stim­u­lus it­self for our thoughts. These neu­rons en­code ex­actly that,” said Quiroga, who is di­rec­tor of the Cen­ter for Sys­tems Neu­ro­sci­ence and head of bi­o­en­gi­neer­ing at the Uni­vers­ity of Leices­ter, U.K.

Many neu­rons fire off elec­tri­cal sig­nals, called ac­tion po­ten­tials, in re­sponse to spe­cif­ic stim­u­li. Which stim­u­li pro­voke sig­nals, and how, dif­fers de­pend­ing on the ex­act cell or brain ar­ea. From this kind of ac­ti­vity, neu­ro­sci­en­tists can fig­ure out which tasks a spe­cif­ic neu­ron is in­volved in­—for ex­am­ple, rec­og­niz­ing spe­cif­ic types of ob­jects or ideas.

In Qui­roga’s stu­dy, for ex­am­ple, a neu­ron that orig­i­nally re­acted only to Whoopi Gold­berg im­ages fired to a “morph im­age” be­tween Gold­berg and Bob Mar­ley only when the sub­ject iden­ti­fied the mor­phed im­age as Gold­berg. That same neu­ron re­mained inac­tive when the sub­ject said the very same im­age was Mar­ley.

The re­search­ers con­clud­ed that neu­rons fire in line with con­scious rec­og­ni­tion of im­ages rath­er than the ac­tu­al im­ages seen. Fur­ther­more, they said, in most cases the neu­ron’s re­sponses to mor­phed pic­tures were the same as when shown the pic­tures with­out mor­ph­ing.

The study is pub­lished in the re­search jour­nal Neu­ron.

“We are con­stantly bom­barded with noisy and am­big­u­ous sen­so­ry in­forma­t­ion,” Quiroga not­ed. “Our brain is con­stantly mak­ing de­ci­sions based on such lim­it­ed da­ta.”

Al­though brain cells cer­tainly ex­ist that re­spond to spe­cif­ic fea­tures of an im­age—down to pre­cise lines and shad­ows—Quiroga said the study shows that some brain cells re­spond to more than just these parts, or even their sum to­tal. They re­port our in­ter­preta­t­ion of the im­age.

The cells were iden­ti­fied in an ar­ea of the brain called the me­di­al tem­po­ral lobe, deep be­hind the tem­ples. These neu­rons may al­so “play a key role in the forma­t­ion of mem­o­ry,” Quiroga said.

“We in­deed see the face of a friend rath­er than the com­bina­t­ion of vis­u­al fea­tures that com­pose the per­son’s face,” he ar­gued. “The neu­rons we re­port in this ar­ti­cle fire ex­actly to this.”

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Scientists have identified some brain cells whose signals reflect our interpretation of an image—not so much the image itself, a study has found. Scientists presented volunteers with photographs that lent themselves to two interpretations: each photo was a cross between two Hollywood celebrities. The information-carrying brain cells, or neurons, were found to fire signals depending on which actor the volunteer took the image to represent. The findings echo a strand of philosophical thought known as British Empiricism as well as the ideas of Aristotle, some 2,400 years ago, said Rodrigo Quian Quiroga, a collaborator in the study. “As Aristotle put it, we create images of the external world and use these images rather than the sensory stimulus itself for our thoughts. These neurons encode exactly that,” said Quiroga, who is director of the Center for Systems Neuroscience and head of bioengineering at the University of Leicester, U.K. Many neurons fire off electrical signals, called action potentials, in response to specific stimuli. Which stimuli provoke signals, and how, differs depending on the exact cell or brain area. From this kind of activity, neuroscientists can figure out which tasks a specific neuron is involved in—for example, recognizing specific types of objects or ideas. In Quiroga’s study, for example, a neuron that originally reacted only to Whoopi Goldberg images fired to a “morph image” between Goldberg and Bob Marley only when the subject identified the morphed image as Goldberg. That same neuron remained inactive when the subject said the very same image was Marley. The researchers concluded that neurons fire in line with conscious recognition of images rather than the actual images seen. Furthermore, they said, in most cases the neuron’s responses to morphed pictures were the same as when shown the pictures without morphing. The study is published in the research journal Neuron. “We are constantly bombarded with noisy and ambiguous sensory information,” Quiroga noted. “Our brain is constantly making decisions based on such limited data.” Although brain cells certainly exist that respond to specific features of an image—down to precise lines and shadows—Quiroga said the study shows that some brain cells respond to more than just these parts, or even their sum total. They report our interpretation of the image. The cells were identified in an area of the brain called the medial temporal lobe, deep behind the temples. These neurons may also “play a key role in the formation of memory,” Quiroga said. “We indeed see the face of a friend rather than the combination of visual features that compose the person’s face,” he argued. “The neurons we report in this article fire exactly to this.”