Brain's mechanism for understanding words and pictures discovered
7 August 2009
For the first time, scientists studying the brain have worked out how
words and pictures paint concepts in our minds. The results are important for understanding how perception and memory
formation occurs.
The research team including Professor Rodrigo Quian
Quiroga at the Department of Engineering of the University of Leicester
in the UK, Professor Itzhak Fried at the University California Los
Angeles and Professor Christof Koch at the California Institute of
Technology in the US. The findings are published online in the journal
Current Biology and will be in the print issue on 11 August
2009.
Professor Rodrigo Quian Quiroga, head of Bioengineering at the
University of Leicester, led the study which concluded that, although
processing of visual and auditory information occur along completely
separate pathways, the visual and auditory processing routes converge to
end up firing the same single neurons.
He said: “Different pictures of Marilyn Monroe can evoke the same
mental image, even if greatly modified as in Warhol’s famous portraits.
This process relates to one of the most fascinating questions in
neuroscience: how do neurons in the brain manage to abstract and
disregard irrelevant details to recognize highly variable pictures as
the same person?”
Professor Quian Quiroga said various studies had provided insights
into how visual information is processed in the brain. He added: “Interestingly, in humans, the same concept of Marilyn can be
evoked with other stimulus modalities, for instance by hearing or
reading her name. Brain imaging studies have identified cortical areas
in the human temporal lobe that are selective to voices and words.
However, how visual, text and sound information can elicit a unique
percept is still largely unknown.”
The University of Leicester team in collaboration with UCLA and
Caltech used presentations of pictures, spoken and written names to show
that single neurons in the human hippocampus and surrounding areas
respond selectively to representations of the same individual using
different sensory prompts.
For example a neuron responded to three
pictures of the TV host Oprah Winfrey, to her name written in the
computer screen and to a computer synthesized voice saying "Oprah";
another one fired to different pictures and the written and pronounced
name of "Luke Skywalker", from the classic movie Star Wars. Another
neuron fired strongly to the pictures and the written and spoken name of
the ex-football star Diego Maradona, even to a picture of Maradona in
the soccer field when his face was not visible but the patient still
recognized as Maradona.
They also found that such degree of abstraction — in the sense that
neurons fired the same to different pictures or the name of a particular
person — increased along the hierarchical structure within the areas they
recorded from.
Moreover, Professor Quian Quiroga found neurons responding to his own
pictures and name, thus suggesting that such neuronal representations
can be generated relatively fast, because he was unknown to the patient
a day or two before the recording took place. He said, “These results demonstrate that single
neurons can encode concepts in a very abstract way, even if evoked by
different sensory modalities.”
The study breaks new ground by demonstrating how neurons previously
studied by the team respond not only to picture, but to written and
spoken names too.
Professor Quiroga continued: “The processing of visual and auditory
information follows completely different cortical pathways in the brain,
but we are showing that this information converges into single neurons
in the hippocampus, at the very end of these pathways for processing
sensory information.
“This work gives us further understandings of how information is
processed in the brain, by creating a high level of abstraction which is
important for perception and memory formation given that we tend to
remember abstract concepts and forget irrelevant details.”
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