Sunday, November 18, 2012

Wires Inserted Into Human Brain Reveal Speech Surprise

Wires Inserted Into Human Brain Reveal Speech Surprise
By Brandon Keim, October 15, 2009

"A rare set of high-resolution readouts taken directly from the wired-in brains of epileptics has provided an unprecedented look at how the brain processes language.

Though only a glimpse, it was enough to show that part of the brain’s language center handles multiple tasks, rather than one.

“If the same part of the brain does different things at different times, that’s a thunderously complex level of organization,” said Ned Sahin, a cognitive scientist at the University of California, San Diego.

In a study published Thursday in Science, Sahin’s team studied a region known as Broca’s center, named for French anatomist Paul Pierre Broca who observed that two people with damage to a certain spot in the front of their brains had lost the ability to speak, but could still think.

Broca’s discovery was made in 1865, but subsequent research has been relatively incremental, reinforcing the language-central role of this area but saying little about what goes on inside it. Speech can’t be tested in any life form other than ourselves, and the standard tool for reading the human brain is fMRI, which averages the activity of millions of neurons at set intervals. It’s useful for highlighting regions of the brain that are involved in cognitive tasks, but can’t detail what’s happening inside those areas.

Sahin’s team benefited from a brain-reading technology called intra-cranial electrophysiology, or ICE, in which electrodes are positioned inside the brain itself. It’s a medical rather than a research tool, used to precisely measure electrical activity in the brains of epileptics who don’t respond to treatment. ICE lets doctors see exactly which parts of a patient’s brain may be surgically removed to prevent future seizures. Though it’s far too invasive and risky to ever be used for academic research, it gave Sahin’s team a chance to watch brains as they processed language.

The patients are “just sitting in a hospital bed, looking at a laptop, and they’re jacked in, with wires right into their brain. And we’re listening to the brain cells talking,” said Sahin. “It’s fantastic that we cold get so close to the actual neural data. Compared to fMRI, it’s like a close-up, high-speed camera where you can see each beat of a hummingbird’s wings, versus taking a picture of the bird flying around a flower.”

During the several days that three patients at Massachusetts General Hospital were medically wired, Sahin’s team asked them to repeat words verbatim, and translate them to past and present tense.

In the space of a quarter-second, a small part of Broca’s area — the only part read by the electrodes — received each word, put the word in a correct tense, and sent it to the brain’s speech centers.

This tested only one type of verbal cognition, cautioned Sahin, and the focus was unavoidably narrow, but it was enough to show that Broca’s area is involved not only in translating speech, but receiving it. That role was considered specific to part of the brain called Wernicke’s area.

More broadly, the findings may represent a general rule for Broca’s area, and perhaps other brain regions: Each part plays multiple roles, rather than performing a single task.

“It’s very distinct from a model where part A does job A. Instead it’s part A doing jobs A, B and C,” said Sahin.

In a commentary accompanying the findings, Max Planck Institute cognitive scientists Peter Hagoort and Willem Levelt said that since Broca’s original observations, “relatively little progress has been made in understanding the neural infrastructure that supports speech production.” The fine-grained Science data “suggests that we are witnessing the ‘first go’ process at work here,” they said.

In further ICE studies of patients, Sahin’s team will study other parts of the language process, as well as the role of Broca’s area in music and movement. In addition to illuminating the brain’s complex choreography, researchers hope the findings will eventually be applied to treating language disorders.

“I’m happy to contribute a piece to the puzzle,” said Sahin. “And the puzzle seems to get more complicated each time you put another piece into it.”


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