Y your brain has a 'Jennifer Aniston cell'
19:00 22 June 2005
NewScientist.com news service
Obsessed with reruns of the TV sitcom Friends? Well then you probably
have at least one "Jennifer Aniston cell" in your brain, suggests
research on the activity patterns of single neurons in memory-linked
areas of the brain. The results point to a decades-old and dismissed
theory tying single neurons to individual concepts and could help
neuroscientists understand the elusive human memory.
"For things that you see over and over again, your family, your
boyfriend, or celebrities, your brain wires up and fires very
specifically to them. These neurons are very, very specific, much more
than people think," says Christof Koch at the California Institute of
Technology in Pasadena, US, one of the researchers.
In the 1960s, neuroscientist Jerry Lettvin suggested that people have
neurons that respond to a single concept such as, for example, their
grandmother. The notion of these hyper-specific neurons, coined
"grandmother cells" was quickly rejected by psychologists as
laughably simplistic.
But Rodrigo Quiroga, at the University of Leicester, UK, who led the
new study, and his colleagues have found some very grandmother-like
cells. Previous unpublished findings from the team showed tantalising
results: a neuron that fired only in response to pictures of former US
president Bill Clinton, or another to images of the Beatles. But for
such "grandmother cells" to exist, they must invariably respond to
the "concept" of Bill Clinton, not just similar pictures.
Wired up, fired up
To investigate further, the team turned to eight patients currently
undergoing treatment for epilepsy. In an attempt to locate the brain
areas responsible for their seizures, each patient had around 100 tiny
electrodes implanted in their brain. Many of the wires were placed in
the hippocampus - an area of the brain vital to long-term memory
formation.
They first gave each subject a screening test, showing them between 71
and 114 images of famous people, places, and even food items. For each
subject, the researchers measured the electrical activity or
"firing" of the neurons connected to the electrodes. Of the 993
neurons sampled, 132 fired to at least one image.
The team then went back for a testing phase, this time showing
participants three to seven different pictures of the initial 132 photo
subjects that hit. For example, one woman saw seven different photos of
the Jennifer Aniston alongside 80 other photos of animals, buildings or
additional famous people such as Julia Roberts. The neuron almost
ignored all other photos, but fired steadily each time Aniston appeared
on screen.
Conceptual connections
The team found similar results with another woman who had a neuron for
pictures of Halle Berry, including a drawing of her face and an image
of just the words of her name. "This neuron is responding to the
concept, the abstract entity, of Halle Berry," says Quiroga. "If
you show a line drawing or a profile, it's the same response. We also
showed pictures of her as Catwoman, and you can hardly see her because
of the mask. But if you know it is Halle Berry then the neurons still
fire."
Given more time and an exhaustive list of images, the team may well
have landed upon other images that spiked the activity of the "Halle
Berry" neuron. In one participant, the "Jen" neuron also fired in
response to a picture of her former Friends cast-mate, Lisa Kudrow. The
pattern suggests that the actresses are tied together in the memory
associations of this particular woman, says Charles Connor, a
neuroscientist at Johns Hopkins University in Baltimore, US.
These object-specific neurons may be at the core of how we make
memories, say Connor. "I think that's the excitement to these
results," he says. "You are looking at the far end of the
transformation from metric, visual shapes to conceptual memory-related
information. It is that transformation that underlies our ability to
understand the world. It's not enough to see something familiar and
match it. It's the fact that you plug visual information into the
rich tapestry of memory that brings it to life."
Journal reference: Nature (vol 435 p 1102)
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