A Neuron's Obsession Hints at Biology of Thought
Brain Cells Are Discovered That Only Respond to Certain Celebrities; One May Worship Homer Simpson but Ignore Madonna
October 9, 2009
By Robert Lee Hotz
Researchers have discovered that in the vast neural network of the brain, some cells are, to use a technical term, celebrity groupies.
|Neuroscientists at UCLA discover single human neurons respond to specific celebrities, including Oprah Winfrey. They say these brain cells show it only takes a simple circuit of neurons to encode an idea, perception or memory.
Probing deep into human brains, a team of scientists discovered a neuron roused only by Ronald Reagan, another cell smitten by the actress Halle Berry and a third devoted solely to Mother Teresa. Testing other single human neurons, they located a brain cell that would rather watch an episode of "The Simpsons" than Madonna.
In one sense, these findings are merely noise. They arise from rare recordings of electrical activity in brain cells, collected by neuroscientists at the University of California, Los Angeles, during a decade of experiments with patients awaiting brain surgery for severe epilepsy. These tingles of electricity, however, gave the researchers the opportunity to locate neurons that help link our perceptions, memories and self-awareness.
In their most recent work this year, the research team reported that a single human neuron could recognize a personality through pictures, text or the sound of a name -- no matter how that person was presented. In tests, one brain cell reacted only to Oprah Winfrey; another just to Luke Skywalker; a third singled out Argentine soccer star Diego Maradona.
Each neuron appeared to join together pieces of sensory information into a single mental impression. The researchers believe these cells are evidence that it only takes a simple circuit of neurons to encode an idea, perception or memory.
"These neurons will fire to the person no matter how you present them," says bioengineer Rodrigo Quian Quiroga at the U.K.'s University of Leicester who studied the neurons with colleagues at UCLA and the California Institute of Technology. "All that we do, all that we think, all that we see is encoded by neurons. How do the neurons in our brain create all our perceptions of the world, all our emotions, all our thinking?"
At its simplest, a neuron is a nerve cell, one of the myriads that make up our central nervous system. Each cell can send and receive the electro-chemical signals that charge our thoughts and emotions.
On average, there are more neurons in the human brain than there are galaxies in the known universe -- about 100 billion in all, arranged on a scaffold of one trillion or so supporting, thread-like glial cells. Our inspirations race through thousands of miles of nerve fibers and axons so compacted that our entire neural network is no larger than a coconut. No two brains are alike, not even those of identical twins.
To these researchers, neurons are the Lego bricks of the brain -- a construction kit that can self-assemble into a cathedral of thought. "The idea of justice is probably generated by a small set of neurons firing," says Caltech biophysicist Christof Koch, who studies the biological basis of consciousness. "It must be true of all the things that we think about ... the number pi ...God."
In some ways, each neuron does act as if it has a mind of its own. Some fire only when they perceive a straight line; others just when they detect a right angle. New neurons form every day. No one knows how the cells can encode a complex thought or how so many neurons can make a mind.
Most of what we have learned about their neurobiology comes through imaging studies, post-mortem analysis or animal experiments. Under normal circumstances, researchers can't directly probe the cells of an awake, living human brain for ethical reasons.
In 1997, though, UCLA neurosurgeon Itzhak Fried and his colleagues started studying epilepsy patients who, as part of normal preparation for surgery, have electrodes implanted deep in their brain tissue. These electrodes are used to record neural activity that could identify the source of the patients' intractable seizures. They also detect the activity of healthy cells around the electrodes, which gives the scientists an opportunity to study the biology of perception and memory. "This really offers us a glimpse into the human mind," says Dr. Fried.
In five provocative experiments since 2005, the researchers used pictures of famous faces and places to screen neurons in brain areas that gather information from all our senses about a person or place we know and blend them into a long-term memory.
To start, Dr. Fried and his colleagues showed eight epilepsy patients 80 images of celebrities, animals, common objects and landmarks while recording the electrical activity of neurons wired to electrodes. They flashed each image for a second, shuffled the sequence into random order and then repeated it. They did that six times.
"You would present hundreds of stimuli -- faces or celebrities or famous landmarks -- and the neuron would respond to only one or two," Dr. Fried says. "The incredible specificity was striking."
In the magazine rack of the mind, some cover girls have a neuron all their own. Testing one patient, the researchers found a neuron that reacted instantly when shown almost any picture of Jennifer Aniston. This cell ignored other celebrities. It gave the cold shoulder to pictures of the actress with her former husband Brad Pitt. "The cells seemed to respond to the idea of Jennifer Aniston," says Dr. Koch.
Testing a second patient, the researchers found a neuron that responded only to Halle Berry. The cell's electrical activity jumped no matter how the actress was posed or how she was dressed. Again, this neuron showed no interest in other celebrities or to any other images of common objects or places.
Subsequent tests turned up single neurons in patients that fired selectively to pictures of former President Bill Clinton, The Beatles, or basketball player Michael Jordan. Each of these individual neurons behaved in a way that made the researchers believe that the cell was responding to a distillation of experience. "The neuron is responding to a concept, not a picture," says Dr. Quian Quiroga. Moreover, each neuron acted as a trigger for recalling the concept they helped encode.
During a follow-up study at UCLA last year, the researchers showed 13 new volunteers wired to neural electrodes a set of 48 short video segments. In part, they wanted to see if neurons attuned any differently to moving pictures and changing scenery.
In fact, some cells did respond strongly to one video clip but not to others. In one patient, the researchers found a neuron that acted up only to The Simpsons cartoon series. "The neuron would spring to life when you showed the video of The Simpsons," says Dr. Fried.
To be sure, few of us likely have a special brain cell devoted to Jennifer Aniston or Homer Simpson. Our cells are sensitive to more than brand names. They can attune themselves quickly to new people or places, often within a day. While monitoring one new patient's brain, Dr. Quian Quiroga was surprised to encounter a neuron that already had him in mind.
"Suddenly," he says, "I find a neuron firing in response to me."
Original source: http://online.wsj.com